Thread: 4 gas appliances in one masonry chimney

Just inspected a home today that had 2 gas hot water heaters and 2 gas boilers, all in one masonry chimney, in the same flue, that is unlined. There does not appear to be any condensate issues. Just wondering what kind of comments this may render.

Russ

The size may not be an issue. Chart in the IRC or National Fuel Gas Code can give you an idea of whether size is a concern. Venting anything into an unlined flue is a concern. And if a liner is installed the reduced area of the flue may be a concern.

I would call it out with no hesitation.

The 4 appliances may or may not be an issue, but the fact that the flue is unlined definitely is.

Realtors have never heard of this before. In areas that have natural gas in old neighborhoods I find it consistently. Today I found a NG hot water heater vented into a masonry chimney. Seems as though that should not be a problem? The forced air furnace was not vented into the chimney. Realtors are going to hate me for calling this out all the time. Oh well.

Originally Posted by Russell Melville

Realtors have never heard of this before. In areas that have natural gas in old neighborhoods I find it consistently. Today I found a NG hot water heater vented into a masonry chimney. Seems as though that should not be a problem? The forced air furnace was not vented into the chimney. Realtors are going to hate me for calling this out all the time. Oh well.

You know where Realtors can go...

The venting of combustion appliances must be to code. If anything is out of whack, it can kill or injure people. I'm really not worried about what some dopey Realtor thinks. Yes, I used to be a Realtor Broker in Charge, GRI. I left it because I couldn't stand the people in the industry.

Originally Posted by Russell Melville

Realtors have never heard of this before. In areas that have natural gas in old neighborhoods I find it consistently. Today I found a NG hot water heater vented into a masonry chimney. Seems as though that should not be a problem? The forced air furnace was not vented into the chimney. Realtors are going to hate me for calling this out all the time. Oh well.

I have a pic of a brick lined chimney with a gas water heater on it. The bricks are soaking wet from the exhaust cooling too soon.

So, having enough heat in the chimney will prevent condensation from damaging the chimney, as the moisture contains the acidic qualities. That is the conclusion that I have come to after much reading. It seems there is no code against venting into masonry with gas appliances as long as it sized properly to produce the heat to warm the chimney. I agree that the best option is to install a liner, but not sure if it is a requirement. Especially with older units and mid efficiency units.

"It seems there is no code against venting into masonry with gas appliances as long as it sized properly to produce the heat to warm the chimney."

From the 2012 IRC: (underlining and bold are mine)
- G2427.5.4 (503.5.5) Size of chimneys.
- - The effective area of a chimney venting system serving listed appliances with draft hoods, Category I appliances, and other appliances listed for use with Type B vents shall be determined in accordance with one of the following methods:
- - - 1. The provisions of Section G2428.
- - - 2. For sizing an individual chimney venting system for a single appliance with a draft hood, the effective areas of the vent connector and chimney flue shall be not less than the area of the appliance flue collar or draft hood outlet, nor greater than seven times the draft hood outlet area.
- - - 3. For sizing a chimney venting system connected to two appliances with draft hoods, the effective area of the chimney flue shall be not less than the area of the larger draft hood outlet plus 50 percent of the area of the smaller draft hood outlet, nor greater than seven times the smallest draft hood outlet area.
- - - 4. Chimney venting systems using mechanical draft shall be sized in accordance with approved engineering methods.
- - - 5. Other approved engineering methods.

It does not meet code, which it seems to me that you are asking about and seeking, and which Bob H. said it needed to meet as a minimum.
- 1. It is not vented in accordance with G2428 as stated for this option.
- 2. This is "for a single appliance" and thus this option does not apply to four appliances.
- 3. This is for "two appliances" and thus this option does not apply to four appliances.
- 4. This option is for mechanical venting systems and thus this option does not apply to natural draft systems.
- 5. Report that the venting needs documentation stating the venting of those four appliances meet approved engineering methods.

That venting does not meet code.

In following these posts, it seems like you are dancing around trying to find a way to say that it is okay - but I could be wrong ... I have been wrong before and will be wrong again - and the only positive thing you can say is "the chimney has not failed YET", then add "documentation is required to show that the venting of the four appliances into the one chimney meets approved engineering methods.

Unless the real estate agent is also a mechanical engineer I would not put any credence to what they say ... they are trying to sell the house, and, from their point of view, no one has died in the house YET ... so the house cannot be too bad.

Originally Posted by Jerry Peck

"It seems there is no code against venting into masonry with gas appliances as long as it sized properly to produce the heat to warm the chimney."


- - - 2. For sizing an individual chimney venting system for a single appliance with a draft hood, the effective areas of the vent connector and chimney flue shall be not less than the area of the appliance flue collar or draft hood outlet, nor greater than seven times the draft hood outlet area.
-

I think that the "nor greater than seven times the draft hood outlet area" provision is what inspectors or installers frequently miss. A 3" diameter flue connector is about 7 square inches. The effective area of a 8"x 8" flue is 42 square inches. That works, but for anything larger than an 8"x 8" flue it would not.

So, as it appears, you cannot make a blanket statement that gas appliances cannot be vented into masonry chimneys?

I could care less about offending realtors, I just don't want to make them hate me because i suggest things that i am not certain about so as to cover my rear and make their job a nightmare. Gas venting in masonry chimneys appears to be one that I can't quite get hold of, and suspect a lot of other inspectors are in the same boat. Any coward can condemn every masonry chimney that has a gas appliance vented into it.

Realtors are not engineers but they trust us to make an accurate determinations, and I find more than not, they truly are looking out for the client, as am I. I hope through this diologue I can come to a better understanding of the subject.

Originally Posted by Russell Melville

So, as it appears, you cannot make a blanket statement that gas appliances cannot be vented into masonry chimneys?

I could care less about offending realtors, I just don't want to make them hate me because i suggest things that i am not certain about so as to cover my rear and make their job a nightmare. Gas venting in masonry chimneys appears to be one that I can't quite get hold of, and suspect a lot of other inspectors are in the same boat. Any coward can condemn every masonry chimney that has a gas appliance vented into it.

Realtors are not engineers but they trust us to make an accurate determinations, and I find more than not, they truly are looking out for the client, as am I. I hope through this diologue I can come to a better understanding of the subject.

There's a difference between an unlined chimney and a masonry chimney. You can make that blanket statement against unlined chimneys, they're not code compliant. If you can find a code compliant, properly sized masonry chimney, you can vent the gas appliance into it.

Originally Posted by lou curley

There's a difference between an unlined chimney and a masonry chimney. You can make that blanket statement against unlined chimneys, they're not code compliant. If you can find a code compliant, properly sized masonry chimney, you can vent the gas appliance into it.

Thank you!!!

I will always call out an unlined chimney as dangerous, if I can determine if it is unlined.

Question is, with a lined chimney that has gas appliance or appliances vented into it, it is not always easy to determine the size of the flue. Cleanouts are not always easy to access, if there is one, or are full, corroded shut, sealed shut with masonry cement, etc? It is quite a stretch to think that I am going to disassemble the flue pipe and measure, or climb a 2 story home with a 8/12 roof pitch, shimmy up a chimney and measure. There is so much more to this, as a chimney that is running up the middle of the home is not going to have the same problems with condensate as a chimney at the exterior, to name one of many. Center mounted chimney will draw more and stay warmer. If I don't see any problems with the chimney concerning condensate or masonry, mortar/flue/cleanout deterioration i don't condemn it as a problem because it has a gas appliance vented into it. It is best, of course, to line it with stainless with a cap. But that is expensive and rarely done in my part of the world, especially with older gas appliances.

Carbon monoxide and smoke detectors are recommended to be upgraded and installed on every report I write. This protects the inhabitants and me.

Originally Posted by Russell Melville

Thank you!!!

I will always call out an unlined chimney as dangerous, if I can determine if it is unlined.

Question is, with a lined chimney that has gas appliance or appliances vented into it, it is not always easy to determine the size of the flue. Cleanouts are not always easy to access, if there is one, or are full, corroded shut, sealed shut with masonry cement, etc? It is quite a stretch to think that I am going to disassemble the flue pipe and measure, or climb a 2 story home with a 8/12 roof pitch, shimmy up a chimney and measure. There is so much more to this, as a chimney that is running up the middle of the home is not going to have the same problems with condensate as a chimney at the exterior, to name one of many. Center mounted chimney will draw more and stay warmer. If I don't see any problems with the chimney concerning condensate or masonry, mortar/flue/cleanout deterioration i don't condemn it as a problem because it has a gas appliance vented into it. It is best, of course, to line it with stainless with a cap. But that is expensive and rarely done in my part of the world, especially with older gas appliances.

Carbon monoxide and smoke detectors are recommended to be upgraded and installed on every report I write. This protects the inhabitants and me.

Why don't you recommend further inspection by a chimney inspector? Whether it is an inside or outside chimney doesn't matter if the flue is in poor repair, improperly sized, or blocked.

Russell, I think the point is, why dance around the one thing in a home that has the single highest potential for killing on injuring the occupants? Why not just call for a Level II inspection by a qualified professional and be done with it. You amatuerish attempts at a partial inspection are telling. For starters, a Level II is indicated upon sale or transfer of the property. Second, if a cleanout is packed full of junk then it is rather obvious what was once a flue liner is now in the cleanout and thus "unlined". Codes have required liners since 1927. If a liner is not intact for the full vent, it must be treated as unlined. You ASSumptions about an interior chimney are actually just tendencies given all things else considered ok. You cannot state that just because a chimney is centrally located that is will have sufficient draft. Testing routinely disproves this theory.

The subject is much more complicated than you're willing to admit or recognize. Get certified or recommend it to someone who is like Lou says. Done. Your statement about being unable/unwilling to climb roofs or attics or use a TV camera or other adjunct to get the 'view into the flue' means you are not doing a level II, which leaves you and your client at risk. Just trying to help.

I think you are missing my point. Of course I would refer a chimney with defects to further review by a qualified individual, and do all the time, as i did with the chimney in my original post. I may be amateurish, but do have a conscience. But it does not seem right to me, as some suggest, that every chimney with a masonry liner is to be considered dangerous/defective if it has a gas appliance vented into it. It is very amateurish to make that statement, and detrimental to me making a living. And if a masonry lined chimney does have gas appliances vented into it and is defective, it is not necessarily defective because of the gas appliance. I call out the defective features of the chimney without making the call as to why it is defective, unless I see visible signs of condensation in/on the chimney or the appliance or vent pipe. There is no doubt that my knowledge of venting is limited, but that does not mean I have to be hyper sensitive and over react.

Originally Posted by Russell Melville

But it does not seem right to me, as some suggest, that every chimney with a masonry liner is to be considered dangerous/defective if it has a gas appliance vented into it.

Russell,

My recollection of the standard to which Bob was referring to is that EVERY MASONRY CHIMNEY should have a Level II inspection - it is required as part of the standard (as I recall).

Whether or not the standard has been adopted in your area does not stop you from referencing it, just like whether or not the latest edition of the NEC has been adopted in your area stops you from referencing it, or the latest editions of the building codes, etc.

The latest editions are nationally recognized standards, whether or not some backward areas refuse to adopt the current standards does not affect home inspectors. In some backward states, like Florida has been recently, which do not adopt current editions of the codes (Florida is still on the 2008 NEC) the code inspectors (like myself) are limited in only addressing what has been adopted and is in force for the project being inspected. I can't say that, because the 2014 NEC says this, that is what I want (actually, I "can" say that, but I would look foolish doing so) as I only have authority to enforce the actual codes as adopted.

Calling for a Level II inspection is for your client's benefit - you can't make them do it, and you don't have to determine or even allude that the chimney is "dangerous/defective", only that a Level II chimney inspection is recommended by the standard. Bob H can fill in the details.

That's basically it Jerry & thx. The fuel has nothing to do with whether it is lined or not. ALL chimneys must be lined-period. The only way to adequately determine whether or not you need a liner is to perform a level II inspection by a qualified professional.

Let me try an analogy: Back when I went through paramedic school, I got praise from the medical control physician when my class was asked what the most important skill was a paramedic held over a basic EMT. There were answers ranging from IVs to defibrillation (electric shock), endotracheal intubation (breathing tube in throat), pleural decompression by needle thoracostomy (needle in chest to relieve tension pneumothorax), etc. I said it was our advance training in assessment of the situation and the patient. You see, there are a lot of backwards EMS programs that send out a basic EMT to decide whether or not to call for the paramedic. I see this chimney issue similarly.

We have a nationally recognized standard dealing with chimney inspections in NFPA 211. Even though it has been voted into law in only a few jurisdictions, courts have still upheld it as the Standard of Care when inspecting chimneys. For real estate sales, transfers, malfunctions or changing fuels, the more comprehensive Level II is called for. You're not even recognizing a full Level I, which is inadequate to determine the suitability of a chimney and liner for continued operation. A level I inspection is intended as the "annual checkup" after a comprehensive level II has been performed and the chimney upgraded to meet 211.

Now, being a Certified Chimney Inspector and an industry trainer means I've done a few level II's and spoken with a LOT of inspectors who have inspected chimneys. I consult on litigation surrounding chimney inspections or the lack thereof. I can state that most masonry chimneys in America as is will fail a level II inspection. There may be many various reasons why but the liners are always a big part of it. The question is: is this chimney suitable for the class of service?

We know chimneys must be lined since 1927. Alternative liner materials have evolved and now we have listed liner systems as alternatives to the more traditional masonry but for now, masonry liners are allowed when the proper materials are used properly. This almost never happens in the wild. So, in order to use a masonry chimney, regardless of fuel, it must be upgraded to meet the class of service.

What do the appliance mfrs. state in their listed instructions? Old manuals used to be very vague. Now, most will reference either "the building code" or NFPA 211 directly. They will also get into whether it is located on an interior vs. exterior wall since they know the tendency of cold exterior flues to suffer from flue gas condensation, weaker draft and backdrafting when compared to warmer interior chimneys *all things considered equal*. They often will flat out state you must reline the chimney when installing an 80% fan assisted furnace. Why is all this? Because they are tired of getting hammered with litigation from masonry chimneys that cannot meet the class of service. Let's explore one example:

Let's say you have a 60,000 BTU/hr. input CAT I fan assisted furnace common vented with a 40,000 BTU input CAT I gas WH that vent into a ubiquitous 16x16" square CMU chimney block chimney in a one story house located in the Mid-Atlantic region. During the winter, the furnace will cycle as much as 5 times per hour during the day losing roughly 12,000 BTU/hr. while firing. During each firing cycle, the first minute is required to dry the surface of the flue tile. The unit continues firing for an addition 3-5 minutes before the thermostat is satisfied then it cycles off. Most furnaces do not have a post-purge on the exhaust so all that last flue gas begins cooling off until it drops below dewpoint where it condenses on the walls of the flue just before the next firing cycle and it repeats. Since there is no draft hood or baro. damper, very little dilution air enters the flue to keep the dewpoint down. Now, with the short firing cycle after the flue surface has dried, there is very little heat left to begin warming the nominal 5/8" terra cotta flue tiles. Remember, a hot flue is a happy flue so we want hot flue tiles to help achieve sufficient draft.

Now, the water heater does fire about 6-8 times per day for about 6 minutes per cycle with similar results. Yes, it does have a draft hood but as soon as the draft dies no more dilution air enters the flue and a CAT I WH is incapable of post-purge. Still, the standing pilot of the WH does add about 600-800 BTU/hr. at standby and the unit loses about 10,000 BTU/hr. when firing, which is still inadequate to warm the flue tiles sufficiently to generate a stable draft.

Now, in the Combustion Appliance Zone is located the air handler for the furnace and the clothes dryer. These are enclosed is a small mechanical closet in the basement, which is less than 50 cubic feet per 1,000 BTU/hr combined input (add in for gas dryer). The return ducts of the furnace are not sealed. Therefore, when the furnace burner cycles off but the air handler is still running, you quickly depressurize the CAZ to where it backdrafts out the draft hood of the water heater into the ambient air in the CAZ where the return leaks entrain it so the duct system becomes a carbon monoxide distribution system. Now, in summer, you do not have the furnace firing but only the WH. With the increased humidity, the flue is dripping wet. The warm outdoor air cools in the flue where the air become denser and thus reverse convection sets in causing a cold backdraft at standby. The water heater firing alone in summertime is often incapable of drying them warming the flue tiles so sufficient draft can be maintained.

Now, you reline the chimney with a low mass thin-walled listed stainless steel liner. It takes only a few hundred BTU's/hr. to warm and dry the liner so a stable draft is quickly established at each firing. At standby the pilot losses are often sufficient to keep the liner dry and a little warmer so it can get "primed" quickly at each firing cycle, unlike the cold, soggy terra cotta tile high mass flues.

As for the depressurized CAZ, you need to require the ducts be sealed with UL 181 mastic or tapes and add makeup air as required.

To combat flue gas condensation, you can recommend a 3-5 minute post-purge timer be installed on the inducer fan.

Now, let's look at your masonry chimney some more. Why does it require a "clean out"? What are you cleaning out? Pieces of flue tile and mortar with gas and oil flues. If you have major soot with gas and oil, those are not common or normal operating conditions and must be repaired. Only solid fuels such as wood or coal generate solid waste in the flue that requires a cleanout even for otherwise acceptable flues. Clean outs are for planned failure. If you find material in a cleanout that used to be up in the flue, then your flue is no longer the same intact flue it once was.

So, what happens in our example when the flue fails to the point is blocks some or all of the flue or it gets blocked by an animal nest or shroud? The furnace has three primary safety controls: vent pressure switch, burner flame rollout switch or fusible link and a high limit switch in the plenum. If you block the flue, the flue gases can and will happily escape the WH draft hood without tripping any of these safeties. Remember, WH's don't have spill switches on their draft hoods per ANSI stds. Let's see if you know the ways to correct this.

Well, I think it would behoove me to follow your advice. I am convinced, and will try to find a way to make recommendations for a level 2 inspection on all masonry chimneys, if I see they do not have a metal liner and cap. I may even add a blanket statement in my chimney section.

Thank you for your patience, and expertise,

Russ M