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  1. #1
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    Default external vent on 85% efficiency furnace

    I am buying a house which has 2 3-year old gas furnaces venting into an old massive chimney (along with gas hot water heaters). Furnace was not lined when furnaces were upgraded, so condensation problems are already beginning to show up. I would prefer that the furnaces (and hot water heaters, which would probably have to be replaced) vent directly to the outside if possible, rather than correcting the chimney problem, as that would end any possibility of CO leaks as well. Is there any equipment which could retrofit these furnaces to an efficiency which would allow this?
    I do not plan to do it myself. However, I much prefer to understand what is being done to make sure it is done correctly. Thanks

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  2. #2
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    Default Re: external vent on 85% efficiency furnace

    They make power vents but if these are not already direct vent type units it would only make sense to line the chimney.
    Vents must be sized correctly and the HVAC tech will have no problem doing it.
    Must admit the post is confusing when you say this is a house but you have more than one furnace and hot water heater.


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    Default Re: external vent on 85% efficiency furnace

    Cost and space wise you are probably best off lining the chimney. A SS liner runs around +/-$1500-1800 around here. Your only other realistic option is installing a B-vent chimney. This would need to run from the basement up through the roof. You would also need a closet space or chase to run the B-vent, enclose the B-vent properly and do the roof work. All of that would easily cost the same or more than a liner.
    Retrofitting the existing furnaces with power venters is NOT recommended. It can be done, however there are several crucial factors that would need to be done properly for it to work safely. Some units can be reasonably retrofitted others can't; the power venter needs to be tied into the gas valve; a retrofit of this type will probably void any warranty.
    Retrofitting the water tank is not realistic.
    Not all HVAC guys are qualified to do this type of retrofit. Be very careful who you hire. Cost to do this for 2 units could easily be close or the same as the liner.
    As far as the scenario you have laid out, a liner is your best, safest option.
    Are you sure the condensation issues are from the units?. Does the chimney have a proper cap and doghouse, is the flashing intact?
    And no you cannot vent these appliances out the side.

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    Default Re: external vent on 85% efficiency furnace

    Thank you both for your response. The house is a duplex, so there are 2 furnaces and 2 hot water heaters.
    I had expected the hot water heaters would not be worth trying to retrofit, but would have to be replaced. I am gathering that a secondary heat exchanger is not available. Are there restrictions on the placement of the outside wall vent relative to other structures?
    Thanks


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    Default Re: external vent on 85% efficiency furnace

    I forgot to add that the chimney's lack of liner was identified by an inspector who crawled around on the roof; I assume he looked at both the flashing and the cap, although I will check again to be certain the chimney was not lined when the furnaces were upgraded.


  6. #6
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    Default Re: external vent on 85% efficiency furnace

    My advice,
    Hire a licensed contractor to reline the chimney for the gas appliance. the rationalization that using a different system to prevent CO in the future is a far reach. A properly installed SS liner will do just that. If you decide to do this yourself keep in mind that most company's will not stand behind the warranty that is offered with the system. A properly Installed Stainless Liner Installed by a licensed contractor is going to carry a lifetime warranty against future issues that may or may not arise. By having multiple gas systems on the liner/liners it would be suggested to have the liner insulated to decrease the moisture that is created in the liner.
    Creating a new chase throu-out the home to vent the appliance throu the roof is going to have a higher cost due to boxing in the system throu every livable space in the home as well as the roof boot and roof work needed.

    Just my take on it.......


  7. #7
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    Default Re: external vent on 85% efficiency furnace

    Quote Originally Posted by ME Stanton View Post
    I am buying a house which has 2 3-year old gas furnaces venting into an old massive chimney (along with gas hot water heaters). Furnace was not lined when furnaces were upgraded, so condensation problems are already beginning to show up. I would prefer that the furnaces (and hot water heaters, which would probably have to be replaced) vent directly to the outside if possible, rather than correcting the chimney problem, as that would end any possibility of CO leaks as well. Is there any equipment which could retrofit these furnaces to an efficiency which would allow this?
    I do not plan to do it myself. However, I much prefer to understand what is being done to make sure it is done correctly. Thanks
    Quote Originally Posted by ME Stanton View Post
    Thank you both for your response. The house is a duplex, so there are 2 furnaces and 2 hot water heaters.
    I had expected the hot water heaters would not be worth trying to retrofit, but would have to be replaced. I am gathering that a secondary heat exchanger is not available. Are there restrictions on the placement of the outside wall vent relative to other structures?
    Thanks
    Quote Originally Posted by ME Stanton View Post
    I forgot to add that the chimney's lack of liner was identified by an inspector who crawled around on the roof; I assume he looked at both the flashing and the cap, although I will check again to be certain the chimney was not lined when the furnaces were upgraded.
    Let me see if I understand your situation correctly, from what
    you have posted:

    FOUR gas-fired appliances, two furnaces, one of which is "85% efficient" and two unknown type or size gas fired water heaters (storage, tankless; draft assisted or not). We do not know the btu ratings for any of these appliances.

    You are thinking about purchasing all of a two-family structure? ("duplex")?

    There are two each, approximately three-year-old gas forced air furnaces of unknown rating (BTUs) that are supposedly 85% efficiency (or are there two or three TWENTY-THREE year-old-furnaces???? I've got to guess this at least WAS a rental or investment (flip) property - I didn't think one could still BUY an 85% gas furnace three years ago. Wonder how old they are (date of manufacture). Air conditioning coils fit? multi-speed blowers? I digress, never mind.

    They are presently vented above the roofline via an exterior masonry chimney which is unlined.Same chimney is also venting (unlined) two gas storage type water heaters of unknown age.

    So far correct?

    I have to start off with I'm not crazy about DIYing or discussing "solutions", but I'm kicking in on this simply because if you're thinking the only expense to in anyway address such a situation as you so vaguely presented is just throwing in a Stainless steel liner for a common vent of four independantly firing gas appliances of unknown rating, size, configuration, etc. for an exterior wall masonry chimney, chase, whatever, and call it safe (who knows the condition of the appliances if having been so improperly vented for however long....) or that sealing same with SS somehow is a CO cure-all, you're due for an awakening. If fuel-fired appliances aren't combusting properly they WILL produce copious amounts of CO. Even if youu had a full length flexible SS flue liner - it won't in and of itself prevent CO from being dumped into the building. There are so many variables....well anyway...lets start with some clarification questions.

    The use of the term "duplex" using a common chimney for venting; could be a regional "thing" still calling such a situation a "duplex" especially after you first refered to it as a house, and the title of the post refers to a single furnace, Lets get the structure pinned down, and if you are purchasing the entirety of the structure - or just one-family-portion, or if this is a two flat apartment building, side-by-side occupancies, multi-floor/story, etc.

    I'd also like to clarify if this is for personal occupancy or as an investment (landlord-renting out both residencies) because this might effect what might be suggested (energy credits, programs, expensing vs. depreciation/etc. also "paybacks" regarding fuel expense, etc.)

    I noted in one of your posts, mention of outside wall and chimney. Need something clarified here - is the masonry chimney on an OUTSIDE WALL?

    It is unknown what equipment was present in the past for heating, nor how it was vented (electric previously?) or prior use of chimney.

    It is unknown the location of these furnaces and water heaters (shared basement "mechanical room", common location for both occupancies, within each residence, etc. other appliances present in same location, etc.).

    Don't know if this is a two-flat apartment building with common entrances/areas, a side-by-side true duplex with separation wall (and/or subdivision-lot whereby "half" may be sold independant from the adjoining), a home with an attached apartment or in-law suite that you're looking to occupy the primary, or what.

    Don't know if there IS a basement with mechanicals, on a slab or crawlspace, or how many levels.Are there separate gas SERVICES for the two occupancies [size/pressure reg. res or larger/higher pressure] natural gas utitlity or propane tank(s)?

    I note your posted location: Wisconsin.

    The above will influance some of what I or others might say. I notice some have presumed a basement, but I don't see where you indicated such. Some have recommended a solitary liner - I find that incredible for four independantly firing appliances something else would be required not just a "liner".

    In the meantime.....Referencing a masonry chimney unlined confuses me - perhaps a chase, or perhaps that means an implied tile flue, don't know.

    Four fired appliances too..outside wall chimney...wisconsin...hmmm.

    You make mention of signs of deterioration and/or moisture problems with chimney - so right off that's a referral for a minimum Level 2 inspection from a CHIMNEY professional - and selecting the right one will also be one who can address your exhaust/venting questions and needs.

    I would NOT at this point go with a "just" a "HVAC" technician for the "chimney" AND venting present situation - Nor would I go with just a fireplace chimney "sweep" type service; You need both a chimney professional will also be able to address and properly assess the venting regards the (presumed storage-type) gas-fired water heaters; and analize combustion/performance of all four appliances;

    Details on the size of the furnaces and efficiency/CATegory type and size/type of water heaters please (storage type, tankless, BTU, fan assist, etc.) If they are in a shared location, mechanical room, laundry facitilites, etc. Need to know this too.

    Improperly vented furnaces/appliances can deteriorate quickly. Sharing with unknown water heaters - potential for host of problems in unlined shared venting - of unknown appliance placement, etc.

    Concern also if using chimney on outside wall even with liners NOT PRACTICAL even IF lined; may be other more effective solutions less prone to PROBLEMS. Need some details/questions answered above, as there are SO MANY possible variables unclarified by the series of posts above. If you could pin down slightly where in WI also, as to which "quadrant" of the state (climatic zone lines running through) it might also "help" a bit - and if property is "out there" versus in a larger city/town or on a farm, etc.

    If this is a rental situation with appliances in a common area like a common basement or such, and utilities are not separated - my first thought without any of the details, and presuming a two-flat rental or a primary home with attached apartment, would be to junk the whole set up (two furances, two gas-fired storage type water heaters, in one presumed location, sharing this unlined, presumed outside wall, masonry chimney, presuming one "service", meter, etc.) Have one high efficiency boiler vented direct; manifold and zoning to provide domestic or potable hot water via mega-stor or similar storage (one for each occupancy) tempered, and hydronic coils in separate air handlers for each "unit" and vent direct using appropriate materials and methods. If you've two metered services, and the appliances are all within the individual occupancies then I'd go with two boilers for DHW and a hydronic coil in air handler skip tank storage for DHW and run the domestic hot water off a coil via a tempering valve and chuck the furnaces; vent each boiler independantly to the great outdoors, and maintain unit/occupancy separations.

    If a "true" duplex - and these appliances are not in a common area, and there is no common area to heat, etc. but within the footprint of each separate occupancy, then no matter what, I'd say two separate venting systems need to be employed - separate and distinct, maintaining separations for the occupancies and clearances/separations for the vents.

    Whatever the situation using a common OUTSIDE WALL masonry chimney/chase with just a liner, is not upon my first impression, the way to go and I haven't devined the specifics yet, but from what little details you have shared - it would seem that simply "lining it" with a singular vent/flue would not be an option. You'd need a means to control draft and prevent back-drafting, yet each individual appliance must be capable of priming, for four independantly firing appliances for two occupancies, two of which wouldn't fire for the non-heating season - cold masonry on outside wall just makes that more difficult to accomplish.


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    Default Re: external vent on 85% efficiency furnace

    See...it is that simple.


  9. #9
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    Default Re: external vent on 85% efficiency furnace

    That brings to question a lot of things I did not even consider..


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    Default Re: external vent on 85% efficiency furnace

    Well the whole "85% efficiency" thing in combination venting above the roof via an unlined CHIMNEY SHARED WITH gas-fired water heaters just doesn't make sense to me.

    An induced draft mid-efficiency furnace intended to be vented out a sidewall (mid efficiency, powered exhaust/induced draft, pilotless ignition individual damper; wouldn't/couldn't be vented as OP suggests, not with w/h's or sharing vent with another and not vented UP an unlined masonry chimney and be even close to 85% actual seasonal efficiency...not to mention all the heat loss due to the WHs. Cat I WHs no way. Power vented/induced or draft assisted WHs again not up a shared vent/flue/chimney above the roof.

    So I'm chewing/kicking on this with a hefty dose of suspicion and more than a few gains of salt, so to speak. It would further seem to me pictures and basic clarifying details should have been initially provided, as conflicting descriptions have already been posted.If any details or clarifications that make the least bit of sense are not quickly forthcoming

    If these are actually somewhere near potentially maximum AFUE 85% gas furances I'm thinking that would be electronic damper, induced/power vented, mid efficiency furnaces - they wouldn't be vented via a chimney to the roof not an unlined chimney for sure; couldn't be anywhere near that efficiency sharing a vent, and to be even close to that efficiency should be be individually vented out a side wall and b-vent wouldn't be the material to vent them in any case.

    Of course its quite possible I could be "out in left field" with "brain-*art-itis"... It happens sometimes to this "old timer", (there I said it, so no one else need be compelled to say it for me) and this might be one of those times (heck I'm mixing metaphores so it very well could be).

    Last edited by H.G. Watson, Sr.; 10-17-2010 at 10:52 AM.

  11. #11
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    Default Re: external vent on 85% efficiency furnace

    I am glad this question is generating so much interest.
    Duplex is a two-flat, Milwaukee area, probably converted from a large single-family bungalow fairly early in its life (built 1920) although that is unknown, could have been designed as it is now configured. There is a common basement mechanical room, with separate meters for both electricity and gas. Owner occupied is the plan, one flat is rented. BTU's of the furnaces not known, but since they were installed 3 years ago they should be properly sized for the spaces involved (have been inspected). Air conditioning units also 3 years old, located outside mechanical room. Hot water heaters are standard tank type, one is 3 years old and the other maybe 20, although both seem to be in good working order. This is a fairly typical arrangement for this region.
    Chimney is internal, which is why I am interested in eventually closing it down, as it takes up quite a bit of floor space in the two smallish flats.


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    Default Re: external vent on 85% efficiency furnace

    Quote Originally Posted by ME Stanton View Post
    I am glad this question is generating so much interest.
    Duplex is a two-flat, Milwaukee area, probably converted from a large single-family bungalow fairly early in its life (built 1920) although that is unknown, could have been designed as it is now configured. There is a common basement mechanical room, with separate meters for both electricity and gas. Owner occupied is the plan, one flat is rented. BTU's of the furnaces not known, but since they were installed 3 years ago they should be properly sized for the spaces involved (have been inspected). Air conditioning units also 3 years old, located outside mechanical room. Hot water heaters are standard tank type, one is 3 years old and the other maybe 20, although both seem to be in good working order. This is a fairly typical arrangement for this region.
    Chimney is internal, which is why I am interested in eventually closing it down, as it takes up quite a bit of floor space in the two smallish flats.
    "ME Stanton"

    I'm just not picking up what you're putting down.

    You titled this topic thread "external vent on 85% furnace".

    You presented yourself as a potential buyer who had just acquired a home inspection and you had questions. I'm not buying it, not one iota.

    A Bungalow is not a "two story". A converted single family home to a Home with attached apartment is not a duplex.

    You're still contradicting yourself.

    No pictures, no specifics (your generalizations with absolutely no details are beyond frustrating) and the story is still changing. Now one of the WHs is just 3 years old.

    Dozens of questions were not answered. Frankly suspicious of any and all information you have presented. You should have information and photos from a professional home inspection report, recommendations; get one. The non-permited/inspected work and apt. conversion can easily verified at the city offices, if any of this was, the details, esp. of the equipment your asking about, would be readily available there; do your homework.

    I don't have high enough boots or waders to don at the moment, and I'm not going to play today.

    Last edited by H.G. Watson, Sr.; 10-17-2010 at 11:36 AM.

  13. #13
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    Default Re: external vent on 85% efficiency furnace

    What do the condensation problems look like?


  14. #14
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    Default Re: external vent on 85% efficiency furnace

    ME your latest post always makes me suspicious. Things aren't adding up. Doesn't sound like you actually got a home inspection. If you did, it was probably some garbage checkbox report. "BTU of furnaces unknown" Really? That should be in the report.
    So you have an old converted Bungalow. The chimney at max with framing would normally take up 2'x2'. Removing it for that type of space gain only makes sense if you are going to a major SF rehab. Multiple B-vents, one for each Apt would take up roughly the same space.
    Condensation from the units doesn't sound like your real issue. No there is no safe way to vent those units out the side.

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    Default Re: external vent on 85% efficiency furnace

    Don't have inspection report yet. I believe the chimney in the attic showed calcification(?) on the outside, other evidence of water seeping through brick.
    The WHs would not be vented to the outside unless replaced with high efficiency models, thus not involved in my inquiry. My only question is if it is possible to vent furnaces outside using power vent (since secondary condenser is not an option) so that large, old, masonry chimney (probably taking up at least 3X3 space in small kitchen, more in basement) could safely be removed without danger using current furnaces, since they are quite new and high-efficiency replacements would be very pricey.
    Thanks


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    Default Re: external vent on 85% efficiency furnace

    Quote Originally Posted by ME Stanton View Post
    Don't have inspection report yet. I believe the chimney in the attic showed calcification(?) on the outside, other evidence of water seeping through brick.
    The WHs would not be vented to the outside unless replaced with high efficiency models, thus not involved in my inquiry. My only question is if it is possible to vent furnaces outside using power vent (since secondary condenser is not an option) so that large, old, masonry chimney (probably taking up at least 3X3 space in small kitchen, more in basement) could safely be removed without danger using current furnaces, since they are quite new and high-efficiency replacements would be very pricey.
    Thanks
    1. Get a Home Inspection then. Any HI worth "salt" will deliver a report in a timely manner.

    2. ALL AUTOMATIC (as to timing/control of operation cycles) FUEL BURNING APPLIANCES such as water heaters, furnaces, boilers, etc. MUST BE VENTED TO THE OUTDOORS/OUTSIDE.

    3. A certified AFUE rating of 85% for a gas furnace does not compute. Not 3-5 years old anyway. Lower or higher, not 85%.

    4. Brand, name, model, Btu rating, serial number information is found on a data plate for the appliance.

    5. If you can't manage that then pay a pro to get that information for you. With that information manufacturer's instructions and installation specifications can be sourced.

    6. You have not been consistant, forthright or forthcoming. The "fact sets" are ever-changing and contradictory. The content and direction of your most recent post is most concerning.


  17. #17
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    Default Re: external vent on 85% efficiency furnace

    Quote Originally Posted by ME Stanton View Post
    Don't have inspection report yet. I believe the chimney in the attic showed calcification(?) on the outside, other evidence of water seeping through brick.
    The WHs would not be vented to the outside unless replaced with high efficiency models, thus not involved in my inquiry. My only question is if it is possible to vent furnaces outside using power vent (since secondary condenser is not an option) so that large, old, masonry chimney (probably taking up at least 3X3 space in small kitchen, more in basement) could safely be removed without danger using current furnaces, since they are quite new and high-efficiency replacements would be very pricey.
    Thanks
    Cat 4 furnaces use schedule 40 and can be directly vented out the side wall.
    There are clearance requirements but they are not all that limiting.
    You also need to deal with local codes as some areas do not allow the pipes in the gangway with noise being a factor.


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    Default Re: external vent on 85% efficiency furnace

    ME,

    As has already been said, your best bet is to get a heating contractor out there to design a solution. Your situation is not uncommon in San Francisco and other older metropolitan areas where single-family homes were modified into multi-family.

    High efficiency (forced-draft) furnaces and boilers will use a plastic pipe for exhaust. These can exhaust in many areas that a B-vent cannot. Much more convenient in older homes than a natural draft furnace.

    Mid-efficiency furnaces typically use a double-walled B-vent, which terminates above the roof, has specific slope needs and clearance requirements.

    On older homes in my area, when using a mid-efficiency furnace, the heating contractor will often run a B-vent (double-walled) along the exterior wall and terminate it above the roof. Does not look good, but it works (at least here in mild CA). This is assuming that these appliances are close enough to an exterior wall to allow them to draft. That kind of solution is typically the most cost-effective when dealing with an existing furnace.

    Installing a B-vent inside becomes a bit more difficult because it will be necessary to do some demolition to install it in a wall cavity. Most people do not want that kind of disruption or expense.

    When installing a new furnace, particularly in a case like the one you describe, I recommend a high-efficiency furnace. The cost of the unit is often mostly offset by the lower cost of installing the B-vent. I recognize that if these are indeed relatively new, replacement of the furnaces would not make economic sense at this time.

    In my, earthquake prone area, I recommend removal or retrofitting of older unreinforced/unlined masonry chimneys. In your area, the deterioration of the mortar and freeze/thaw will be other considerations.

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  19. #19
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    Default Re: external vent on 85% efficiency furnace

    Quote Originally Posted by Gunnar Alquist View Post
    ME,

    As has already been said, your best bet is to get a heating contractor out there to design a solution. Your situation is not uncommon in San Francisco and other older metropolitan areas where single-family homes were modified into multi-family.

    High efficiency (forced-draft) furnaces and boilers will use a plastic pipe for exhaust. These can exhaust in many areas that a B-vent cannot. Much more convenient in older homes than a natural draft furnace.

    Mid-efficiency furnaces typically use a double-walled B-vent, which terminates above the roof, has specific slope needs and clearance requirements.

    On older homes in my area, when using a mid-efficiency furnace, the heating contractor will often run a B-vent (double-walled) along the exterior wall and terminate it above the roof. Does not look good, but it works (at least here in mild CA). This is assuming that these appliances are close enough to an exterior wall to allow them to draft. That kind of solution is typically the most cost-effective when dealing with an existing furnace.

    Installing a B-vent inside becomes a bit more difficult because it will be necessary to do some demolition to install it in a wall cavity. Most people do not want that kind of disruption or expense.

    When installing a new furnace, particularly in a case like the one you describe, I recommend a high-efficiency furnace. The cost of the unit is often mostly offset by the lower cost of installing the B-vent. I recognize that if these are indeed relatively new, replacement of the furnaces would not make economic sense at this time.

    In my, earthquake prone area, I recommend removal or retrofitting of older unreinforced/unlined masonry chimneys. In your area, the deterioration of the mortar and freeze/thaw will be other considerations.
    Thank you, this is the type of info I have been seeking. Building a new interior chase would be problematic as both first and second subfloors are concrete. An outside B-vent could be a possibility (one I had already considered) subject to code restrictions, which I haven't checked yet. Are power vents for the furnaces a possible alternative, if correctly installed?


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    Default Re: external vent on 85% efficiency furnace

    Congrats ME, you have been called a liar and an idiot after only a few posts! I have been watching this forum for awhile, that may be a new record.
    Since a few finally gave you a coherent answer, maybe I could offer a bit more advice. The answer may be, as others have suggested, to install high efficiency Cat IV furnaces and an induced draft water heater, all of which can be vented through PVC out a side wall. You will probably pay for them reasonably quickly with the gas savings. Real estate where you are is fairly pricey, the square footage gained by removing the chimney is a valuable bonus.
    Another option may be to install electric heat pumps and electric water heaters. There are nice tax incentives for high efficiency heat pumps.

    A couple of points, I understood immediately the scenario you were describing as I'm sure most readers did. There's nothing complicated about an unlined chimney, we who actually perform inspections see them frequently.
    Also, there is nothing in the ASHI or any other standards that I know of that require the home inspector to determine the BTU input or output of the furnace, that may or may not be in your home inspection report.


  21. #21
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    Default Re: external vent on 85% efficiency furnace

    Quote Originally Posted by ME Stanton View Post
    Thank you, this is the type of info I have been seeking. Building a new interior chase would be problematic as both first and second subfloors are concrete. An outside B-vent could be a possibility (one I had already considered) subject to code restrictions, which I haven't checked yet. Are power vents for the furnaces a possible alternative, if correctly installed?
    ME,

    An interior chase might not be necessary. BW vents are oval versions of B-vents and are designed/intended to be run inside a wall cavity. Of course, this would mean breaking into walls, which is messy. Interesting that you have concrete subfloors. Is that a lightweight concrete to reduce noise transmission through the floor? I have only seen something like that once or twice. If so, it might only be an inch or two thick, or even poured after the interior walls were framed. If that is the case, it would not be necessary to break through the concrete if BW vents were used in existing wall cavities. DuraVent

    Unfortunately, I know nothing about power vents, I am a lowly home inspector and furnace system design is beyond my knowledge. The current mid-efficiency furnaces (at least those that I see) have an inducer fan that starts the draft, but this is not the same as a forced-draft that you would find on a Catagory IV. I have not seen a power vent on a furnace.

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    Default Re: external vent on 85% efficiency furnace

    That's two posters now and three posts:

    carrying on about a SINGLE furnace.

    The title of the thread does not match the story,

    "As the story turns":

    Two furnaces, one for each occupancy in a common location; and two gas fired storage type CAT 1 water heaters, one for each occupancy; ALL in the same common location, the BASEMENT "Mechanical Room".

    That's FOUR fuel-fired appliances. All independantly firing; in a four-season climate. All venting in a common masonry chimney, which passes through both occupancies, one occupancy over the other.

    A masonry chimney of a 1920s "Bungalow" (now with supposed concrete subfloors on first and second level above basement). 1920s Milwaukee, Wisconsin, chimney would have likely been for coal heating source, later converted to gas. Obviously this residence was once heated and hot water supplied with singular appliances. Seems that was changed three years ago with installation of two furnaces and a second water heater.

    As the story turns, starts off with concerns about the "massive" unlined chimney; which is so massive its exterior footprint in the basement is 3x3' then is reduced to 2x2' Claims has had home inspection, yet still awaiting report and photos and now its two or three days later. Opines that the 20 year old Cat 1 DWH and the 3-years new DWH will likely need to be replaced; remarks about deteriorating/moisture problem with the chimney, OP blames the problem on it not having been lined when the Two to replace one furnaces and second additional water heater were installed 3 years ago, and desires to somehow "convert" two "85% efficiency" gas furnaces (or are they?) to some sort of DIY "power vent" out the side wall of the basement!


    Gunnar (in Santa Rosa, California),

    You're telling (designing?) OP in Wisconsin to vent the four appliances to a common exterior b-vent and run it out the side of basement wall and up the side of the now two story two-family home (apparently former attic apartment), or build a chase or chimney on the exterior of the building, or to run A (single) bw in the exterior wall cavity! 2 furnaces and 2 water heaters vented from the basement. Are you SERIOUS?

    85% efficiency would = 15% flue loss which would not be a Cat I Fan assisted gas fired furnace. Cat I fan-assisted = 17% or greater flue loss.

    Cat II & Cat III (and Cat. IV) require special venting.


    Milwaukee, Wisconsin. 2500-2999 Heating Load Hours. SNOW. COLD, FRIGID WINTERS. HOT Humid Summers. TWO furnaces, TWO water heaters in Basement. TWO occupancies, second over first.

    Last edited by H.G. Watson, Sr.; 10-18-2010 at 11:42 PM.

  23. #23
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    Default Re: external vent on 85% efficiency furnace

    HG,

    Please do not respond to any of my posts again. No kidding.

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    Default Re: external vent on 85% efficiency furnace

    85% efficency / 15% flue loss.

    Cat. I fan-assisted gas-fired furnace = 17% or greater flue loss.

    Cat. II & III (and IV) require special venting.


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    Default Re: external vent on 85% efficiency furnace

    It seems to be that what ME is really looking for is someone to tell him that there is some proper and safe way to:
    a) get rid of the brick chimney, and
    b) vent his units out a side wall
    So to once again answer your question from Post #15, the answer is somewhere between NO and highly doubtful.
    Referring to the SOP's as an excuse not to put the BTU size of the furnace in the report is pretty pathetic. So what you don't write down the model number either, so you don't take off the cover panel and take a look? Not only is that lame but dumb.

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    Default Re: external vent on 85% efficiency furnace

    Quote Originally Posted by Gunnar Alquist View Post
    ME,

    An interior chase might not be necessary. BW vents are oval versions of B-vents and are designed/intended to be run inside a wall cavity. Of course, this would mean breaking into walls, which is messy. Interesting that you have concrete subfloors. Is that a lightweight concrete to reduce noise transmission through the floor? I have only seen something like that once or twice. If so, it might only be an inch or two thick, or even poured after the interior walls were framed. If that is the case, it would not be necessary to break through the concrete if BW vents were used in existing wall cavities. DuraVent

    Unfortunately, I know nothing about power vents, I am a lowly home inspector and furnace system design is beyond my knowledge. The current mid-efficiency furnaces (at least those that I see) have an inducer fan that starts the draft, but this is not the same as a forced-draft that you would find on a Catagory IV. I have not seen a power vent on a furnace.
    Thank you for your insights. Obviously the needs of the furnaces will need to be carefully assessed. Power vent was (very cautiously) suggested in another post; that will also be subject for investigation. Unfortunately concrete floors are 6" thick, which may seriously complicate routing BW pipe up walls. (The seller said that the house was originally built by a concrete contractor. There are terrazzo floors all over the place, including the garage.) If anyone knows a good web site for mechanical design issues, I would be grateful for a link.

    As previously mentioned, water heaters are not part of the question. They would be replaced by high efficiency which vent through PVC pipe if alternative to chimney can be found.


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    Default Re: external vent on 85% efficiency furnace

    Well into at least the second business day post-supposed "inspection".

    Make and MODEL numbers of these supposed 85% efficient gas-fired furnaces in the basement still lacking. Not one detail to support the "story". Not a single coherent piece of information. Not a photo, nothing.

    Am I the only one that is "questioning" that this/these couldn't possibly (as described) be Cat-I fan-assisted gas-fired furnaces? That they must be (even in a perfect world dedicated venting) if certified "85% EFFICIENT" at a minimum would be considered to be condensing and classified as OTHER THAN CAT. I?!??

    A basement - two occupied floors above, and at least a roof. Milwaukee Wisconsin. Un-lined masonry chimney from the basement used for venting as the story goes. OP has called this chimney "massive", mention of its outside "footprint". Unknown what the flue area, height, projection above the thermal envelope and roof are, etc..

    The mass and BTUs it would require to minimally prime such (unlined masonry chimney) especially during a Milwaukee Winter. Would be enormous, even an interior unlined masonry chimney, still enormous by comparison to other venting. Thermal conductivity poor. Vintage of the structure (stated 1920s) unknown STATE/STATUS of vintage and history of masonry "chimney".

    Hence further inquiry regarding the ratings of the appliances, and other "questions" and "suspicions" - mention made of "issues" already with Chimney.

    Out of the "starting gate", at a minimum referal to a chimney professional if considering for any use/purpose, and even to determine if same to leave in-place seal off and abandon! Structural integrity even if considered as a chase for a vent or liner, should that even be appropriate.

    At 85% efficiency certified AFUE "out of the box" we're talking COOLER exhaust temps. With the MASS and relatively poor themal conductivity of a masonry chimney, even one enveloped by a conditioned structure - still a problem. Unheated basement source even worse. How much heat loss to the basement via connector(s)/manifolds?

    Is anyone picking up what I'm putting down? Am I having an old-timers, blinders-on combination brain malfunction?

    If not one of the four appliances in the basement is a straight draft-hood (no fan assist) Cat-I appliance - NONE may be vented through an unlined masonry chimney. Even if one (non-draft assisted Cat I) is present - SHOULD even it (let alone all shared) be? (likely NO) (2-story over basement appliances).

    Is there any type of controlled firing sequence or controlled tandem start-up for any of these four appliances?

    It seems to me at a minimum the masonry chimney could/would/should be abandoned. Even lined -overcoming "issues" with condensation, draft, etc. A chase can be errected in its place with stops, etc. to contain, if venting for any of the appliances in the basement require to vent through to above the 2-story (+/-attic) roof. I'm thinking if its true that these furnaces are certified 85% efficiency they likely shouldn't be anyway.

    I said I wasn't going to play with the OP, but contributons from others got me going. Hopefully I've explained my thought process, wrong or right, off-the-wall or on-the-mark, or somewhere in between.

    Without something, anything, some sort of "pinned down" definitive fact set and specific clarifications; discussing this further is nothing but futile except to refer to professional and warn of possibilities of danger? (structural integrity, fire, CO poisoning, corrosive conditions, damage to equipment) etc.?

    Last edited by H.G. Watson, Sr.; 10-19-2010 at 09:37 AM.

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    Default Re: external vent on 85% efficiency furnace

    I have to agree with you on many fine points HG.
    I don't think these are any kind of real 85% units. Never mind that I've never seen such a rating tag. I've been thinking that these are 'newer' old model conventional units that are being pawned off to someone (maybe ME) as some sort of mid-efficiency units.
    Based on his latest post, this is NOT a bungalow by any conventional use of the word. Or maybe I'm just the dummy who doesn't know about that era of concrete bungalows with 6" thick floors. The size of the chimney doesn't make sense either.
    I'm also suspecting there was no HI done. There were two days between his original OP and when he stated he didn't have a report yet. Since IL, WI & IN, have reciprocal licensing of some sort, I'm guessing he should have had the report within 2 days. Definitely had it by now.
    Since we now 'know' that this is a concrete building, I would say that 'unconventional' venting methods are the last thing one would want to install. The assumption being that the building is probably tighter than a conventional real bungalow. Probably also has old aluminum windows that will be replaced with new tighter windows.
    When info doesn't add up, one just has to wonder ...

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    Cool Re: external vent on 85% efficiency furnace

    At 85%, you would have to be a condensing unit because above 83% the only heat left is latent heat in the water vapor. That makes it a CAT III or CAT IV, both of which are vented mechanically. CAT II is a theorectical category but cannot be achieved in practice since there is not sufficient stack losses to generate a natural draft sufficient to vent the appliance.

    Keep the fire in the fireplace.

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    Default Re: external vent on 85% efficiency furnace

    Quote Originally Posted by Bob Harper View Post
    At 85%, you would have to be a condensing unit because above 83% the only heat left is latent heat in the water vapor. That makes it a CAT III or CAT IV, both of which are vented mechanically. CAT II is a theorectical category but cannot be achieved in practice since there is not sufficient stack losses to generate a natural draft sufficient to vent the appliance.

    Thank you Bob!


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    Default Re: external vent on 85% efficiency furnace

    Inspection report, which I now have (apparently sent originally weeks ago to wrong email address) states furnaces are "mid-efficiency." Cannot look at them as have no access to house yet. Copied from report:
    BRAND
    Carrier.
    TYPE
    Mid-efficiency.
    FUEL
    Gas.
    AGE
    Approximately 3 years old.
    EXHAUST FLUE
    Metal. Inspected.

    So mid-efficiency is not 85%, as I was told? Thanks


  32. #32
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    Default Re: external vent on 85% efficiency furnace

    Quote Originally Posted by ME Stanton View Post
    Inspection report, which I now have (apparently sent originally weeks ago to wrong email address) states furnaces are "mid-efficiency." Cannot look at them as have no access to house yet. Copied from report:
    BRAND
    Carrier.
    TYPE
    Mid-efficiency.
    FUEL
    Gas.
    AGE
    Approximately 3 years old.
    EXHAUST FLUE
    Metal. Inspected.

    So mid-efficiency is not 85%, as I was told? Thanks
    ME,

    Mid-efficiency is 80%. I wonder if maybe you were told 85,000 BTU, mid-efficiency rather than 85% efficient. Doesn't really matter.

    The one curious thing that I notice is the metal exhaust flue remark. I have not looked back at the earlier posts, but I recall this being vented through a masonry chimney. Does the metal vent stop at the masonry chimney or is it run up inside? Not likely, but I thought I would ask.

    It seems as though you still need the opinion of a heating contractor. Ask him for alternatives and prices as well as his opinion. I suggest avoiding the contractor that did the current install. I am uncomfortable with venting all of those appliances into the existing masonry chimney. I really believe that they should have been vented using B-vent or BW-vent.

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    Default Re: external vent on 85% efficiency furnace

    Quote Originally Posted by Gunnar Alquist View Post
    ME,

    Mid-efficiency is 80%. I wonder if maybe you were told 85,000 BTU, mid-efficiency rather than 85% efficient. Doesn't really matter.

    The one curious thing that I notice is the metal exhaust flue remark. I have not looked back at the earlier posts, but I recall this being vented through a masonry chimney. Does the metal vent stop at the masonry chimney or is it run up inside? Not likely, but I thought I would ask.

    It seems as though you still need the opinion of a heating contractor. Ask him for alternatives and prices as well as his opinion. I suggest avoiding the contractor that did the current install. I am uncomfortable with venting all of those appliances into the existing masonry chimney. I really believe that they should have been vented using B-vent or BW-vent.
    Thanks for the clarification. I am sure I was told 85%, apparently erroneously. But I gather from your comment that the B-vent is the appropriate one for a furnace of this type. These can be run up an outside wall to the roof, can they not? That may be my only option, given the concrete floors and my desire to remove the chimney.
    I appreciate your thoughtful responses.


  34. #34
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    Default Re: external vent on 85% efficiency furnace

    Quote Originally Posted by ME Stanton View Post
    Thanks for the clarification. I am sure I was told 85%, apparently erroneously. But I gather from your comment that the B-vent is the appropriate one for a furnace of this type. These can be run up an outside wall to the roof, can they not? That may be my only option, given the concrete floors and my desire to remove the chimney.
    I appreciate your thoughtful responses.
    ME,

    Yes, with a mid-efficiency (80%) furnace, a B-vent is the material to use. I am not sure if it can be run up the exterior in your area. It is done like that around here, but we have a much milder climate. That would be something to talk to a heating contractor about. Maybe someone else from the board will chime in.

    Once again, without really seeing everything that is there, I am making reasonably educated guesses. You really need to get a heating contractor to design an solution.

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    Default Re: external vent on 85% efficiency furnace

    Quote Originally Posted by Gunnar Alquist View Post
    ME,

    Yes, with a mid-efficiency (80%) furnace, a B-vent is the material to use. I am not sure if it can be run up the exterior in your area. It is done like that around here, but we have a much milder climate. That would be something to talk to a heating contractor about. Maybe someone else from the board will chime in.

    Once again, without really seeing everything that is there, I am making reasonably educated guesses. You really need to get a heating contractor to design an solution.
    And, probably not just any heating contractor. I'll be looking into it. Thanks to everyone for all the information.


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    Default Re: external vent on 85% efficiency furnace

    I guess we're just ignoring CAT III mid-efficiency furnaces.


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    Default Re: external vent on 85% efficiency furnace

    As I recall, Gunner told you not to respond to his posts. Please respect that.


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    Default Re: external vent on 85% efficiency furnace

    Quote Originally Posted by Benjamin Thompson View Post
    As I recall, Gunner told you not to respond to his posts. Please respect that.
    You aren't the boss of me, and with all due respect to Gunnar, neither is he.

    I did not direct my post to Gunnar.

    This is an open forum. There are rules for this forum which are presented by our host and to which we are supposed to abide.

    My post was to the topic discussion, those who have participated on it, and to the Original topic and poster.

    It was on topic and pertained to the discussion.


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    Default Re: external vent on 85% efficiency furnace

    Quote Originally Posted by H.G. Watson, Sr. View Post
    You aren't the boss of me, and with all due respect to Gunnar, neither is he.
    Ohhh, but I AM "Prof". Take this as your first warning. I will take your word this time that you were NOT responding to Gunnar's post.


  40. #40
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    Default Re: external vent on 85% efficiency furnace

    H.G. does that stand for Hot Gas.

    Tom Rees / A Closer Look Home Inspection / Salt Lake City, Utah

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    Exclamation Re: external vent on 85% efficiency furnace

    Quote Originally Posted by Benjamin Thompson View Post
    Quote Originally Posted by H.G. Watson, Sr. View Post
    You aren't the boss of me, and with all due respect to Gunnar, neither is he.
    Ohhh, but I AM "Prof". Take this as your first warning. I will take your word this time that you were NOT responding to Gunnar's post.
    ??????

    Last edited by H.G. Watson, Sr.; 10-23-2010 at 09:03 AM.

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