Thread: Cat IV Wall termination

"The vent terminal shall be installed a minimum of 14-inches from any obstruction".
I have read this statement in a few places but cannot find the coded reference. Any help?

Does anyone have the manufacturer's instructions on an American Standard Model # ALCIB060A9361AE Cat IV non-direct vent. I did not get anything with Google.

I need some coded or manufacturer's references to refute this Cat IV termination set-up. A box was built over it on the deck.

I have the NFPA Chapter 12 references but can't seem to find that this set up is a problem.

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Originally Posted by Mike Lamb

"The vent terminal shall be installed a minimum of 14-inches from any obstruction".
I have read this statement in a few places but cannot find the coded reference. Any help?

Does anyone have the manufacturer's instructions on an American Standard Model # ALCIB060A9361AE Cat IV non-direct vent. I did not get anything with Google.

I need some coded or manufacturer's references to refute this Cat IV termination set-up. A box was built over it on the deck.

I have the NFPA Chapter 12 references but can't seem to find that this set up is a problem.

If it doesn't meet all the cxriteria for direct vent sealed combustion chmber then it is not a Cat IV installation. A true Cat IV direct vent installtion can be other than concentric venting materials, can only presume you mean it is not a sealed combustion chmber equipped furnace then. So the underlined and bolded of the quote above still doesn't make sense.

The deck you've pictured is occupied.

The under deck and deck box in the first picture I presume is immediately above the terminal and intake you're showing in the second picture.

The terminal and intake appear to be restricted in side wall projections of the deck joists/support system. The occupied decking (deck floor) is the roof or ceiling area for the space below. It is unknown how far out that deck extends, how much distance to the left or right, what the elevation is, or if the area below the deck is further restricted as to air flow - the adjacent fence, I presume is very close - and further acts as a side wall.

Review the restrictions regarding under porch with side walls, air flow.

Although you didn't indicate which edition of NFPA 54 you're referencing it would be wise to consult that which was the most current edition at the time/date of manufacture of the appliance.

However, from the "looks" of things, and unknown jurisdiction Home Rule additional restrictions regarding decks, etc. and your photos & description, there appears to be several areas of concern regarding the terminal & intake. Not the least of which would be the corrosive nature of what comes forth from the terminal - adequate dillution air at same, and the effects of condensate and corrosive effect upon the apparent galvanized hanger & fastener system, the aluminum or galv EMT directly below, mortar, the decking restricting the terminal & intake, and the health & safety of the occupants upon that deck and wood deck box overtop which I presume to be about a 3-4 four foot elevation and rather deep as well as wide. Cannot see where the door opening to the home might be in relation to the terminal & intake.

Covered porches, alcoves, sidewalls, elevations, unknown basement or crawl vents, windows, eeros, etc?

I also have concerns regarding the attachment/support structural system of the deck, and doubt the permit/acceptance status of what I see in the pictures and the various home rule jurisdictions for the greater Chicgo area.

Lets start off with getting what I've bolded & underlined clarified, the specifics of the installation, complete data plate information, then move forward with the correct references. "Non-direct vent + Cat. IV" = "does not compute" 'on this end'.


P.S.

American Standard acquired Trane in 1984. The company is a subsidiary of American Standard and sells residential and commercial HVAC equipment and systems. So, technically, one could say that American Standard makes Trane furnaces. Ingersoll-Roll acquired Trane, Inc. / prev/K/A American Standards Companies section in 2008.

First letter A - branded Amer Stan, First Letter T - branded Trane.

HTH.

Sources:

Learn More About Trane

History

HG, it's a Cat IV 60K furnace with a non-direct vent installation. The second vent you see is for a water heater. Clearance to doors, windows, etc. is not an issue.

The local gas company says this:
1. The vent shall not be installed in an inner court or light well that is enclosed on all four sides.
2. The vent shall not be installed in an outer court or any other similarly restricted area (e.g., gangway) unless there is a minimum distance of 10 feet from the nearest building.

I believe the, "similarly restricted area," in #2 may apply. I'm looking for real references prohibiting this set-up.

ML,

We are not communicating well. Perhaps I'm misfiring on this end (my brain or communications or both), that's been happening more often than I'm aware of these days.

First The model number format isn't matching format wise a furnace, at least my materials pre IR.Recheck pls your notes and/or your shot of the data plate.

Next, an alternate installation of what would otherwise be a DV Cat IV furnace when installed as to the initial ratings, instructions, etc.; is no longer a Cat IV, Direct Vent Instllation when an ALTERNATE intallation method and venting is employed, becomes a Cat II or III, type application/installation depending on the equipment, rating, performance, and mfg instructions for alternate installation method provided for and followed.

Both (now identified as terminals for 2 different applinces) are dumping and obstructed by the floor and structure deck - corrosive condensation ladden exhust.

If the furnace has been installed other than DV (no inlet at same plane, etc. terminal location) then it is not a DV Cat IV installation. Cat IV installations are DV, if not Direct vented in its instllation application its not Cat IV.

Please recheck your model number and SN from your notes or photo of data plate and re-review your NFGC (NFPA 54). Lets get more precise regarding mfg date.

Lets try starting off with identifying the equipment with the correct & complete full Model Number and serial number and aging the equipment to get you to the most correct and appropriate information including appropriately matching mfg instructions.

FYI Am St/Trane Furnace model nomenclature sample/example, see Table titled American Standard/Trane Inc. for an example of later (more recent) furnace model numbers' cell break-down link below

http://www1.eere.energy.gov/building...ler_app7_2.pdf

crawl space or half basement equipment home?

examples of differing serial number formats used for mid 80s plus american standard branded furnaces in the more recent past (not pre mid 70s prior AmSt branded generational equipments) below link.

manufacture or age of an AMERICAN STANDARD® furnace or other AMERICAN STANDARD® HVAC unit | Building Intelligence Center

see esp. the last cell/slide at the bottom of the page. Keep in mind the 'history' skips over prior Am St 60s to early 70s furnace divestiture pre-Am bk re-org but N/A as was time much prior to other than lower eff cat I.See also previous links. Somewhere you should be able to find an active telephone number to assist you with locating the complete and correct data plate information (Trane Inc. now owned by IR).

p.p.s. Sry for formatting errors earlier with links etc. computer (internal & external) not playing well with www today.

Again, HTH.

HG, where are you drawing from claiming all CAT IV appliances must be direct vent?

From the 2009 IRC, Ch. 24 Fuel Gas, definitions:
"Vented Gas Appliance Categories"
Category IV. An appliance that operates with a positive vent static pressure and with a vent gas temperature that is capable of causing excessive condensate production in the vent."

There is no requirement for direct venting to be CAT IV. Now, a CAT IV may be direct vented but it can be one piped, which is not direct vent and still meet the listed instructions as a CAT IV gas appliance.

Def. of Direct-Vent Appliances."Appliances that are constructed and installed so that all the air for combustion is derived directly from the outside atmosphere and all the flue gases are discharged directly to the outside atmosphere."

Gas direct vent fireplaces are no where near condensing and thus not CAT IV. You can have a CAT IV water heater that is single piped so it is not direct vent but still CAT IV.

sealed combustion chamber, B.H. perhaps the personl 'internl computer' is having a glitch, wouldn't be the first nor the the first 30th in the lst few wks.

Non direct vent installation still using outside air (intake and termination vent not on same plane such as venting through the roof or chimney) or intake low alternate plane & vent high vs. using inside air loss of efficiency and loss through vent terminal loses Cat IV status efficiency loss +17%. A 90% DV Cat IV designed can lose efficency with alternate installations & ecessive long oversized vent runs roof & function below 83% eff. esp. single stage installed in above ground vented crawl.

HG is a little confuzzled.

From a Trane Cat IV installation manual. Page 19.

http://www.munchsupply.com/UserFiles...l%20manual.pdf

HORIZONTAL VENTING THROUGH WALL: These furnaces may be installed as direct vent (as shipped) or as nondirect vent. Installation must conform to national, state, and local codes.

Originally Posted by H.G. Watson, Sr.

sealed combustion chamber, B.H. perhaps the personl 'internl computer' is having a glitch, wouldn't be the first nor the the first 30th in the lst few wks.

In medicine, we refer to that a "cerebral flatulence"

I have recommended improvements in this termination on the grounds that the corrosive effects of the condensate in this confined space are going to eventually destroy everything that comes in contact with it, and in very cold weather there's going to be some serious frost problems.

I think that is the best I can do for now. I'm still trying to find the installation instructions for this particular model furnace.

American Standard model # AL C1B060A9361AE

FYI

An American Standard tech sent installation instructions on what he thought was the furnace in question. I guess I have the model # wrong. It is vague.

A Rheem pdf is far clearer than the A.S. on this subject.
http://www.rheem.com/documents...ructions

5. 6 feet from an inside corner formed by two exterior walls ? 10 feet is the recommended distance.

1. Do not terminate under any kind of patio or deck.

I also read someone's install guide that stated, 'not under a deck or patio' or something similar, can't remember who's though.
I don't like the install either. However, in situations like this it can be more helpful to the client to concentrate on the consequences rather than whether it is allowed or not.
- You've got acidic discharge under the deck next to joist hangers and a conduit run. I've seen some pretty ugly conduit and joist hangers from furnace exhaust. The wolmanized will probably survive. Is the client going to go under the deck annually to assess the conduit and joist hangers? probably not.
- You stated the other pipe is not inlet but a hot water tank. That's what I would concentrate on. That would be in my report as D&H. The furnace, who's going to sit out there in the winter when its on, probably no one. The hot water tank however will be ON during warm weather when people are out there or little kids are under the deck playing house or whatever. I would report the safety hazard due to potential exposure. My guess is that ugly bench was installed because someone already wrote the pipes under the deck for occupant exposure.
- Joist hangers don't look fully nailed
- Lineset holes don't look sealed

A "C" in the correctly transcribed model number would indicates a condensing furnace which is not a Cat IV. X or Y indicates a Cat IV Condensing candidate furnace when installed DV. I mentioned early on my doubts as to the accuracy of the model number + branded identification of 'furnace' not consistant with AmSt/Trane,Inc. of unknown age, type, style, and fuel source. My questions to the op were not answered - such as orientation of unit, location (crawl vented/unvented, half or full basement), etc. and serial number info (age, factory location) etc.obstructions to terminal end are unacceptable. I noted further concerns regarding the occupied deck hazards to ppl & structure regarding terminal/inlet later corrected by OP as two terminals, two appliances.

I further suspect the "I" (i) is a "1" one, and the "B" may be a '6', 'G' or an '8'. and that this is not the "model" number. One of those "picture worth a thousand words" and 20 words further were additionally requested.

Sadly, no flatuance can be blamed, metastatic. A paraphrase of Billy Martin, 'wont have' H.G. 'to kick around anymore' soon enough.

Trying again...(surely to regret it later) to communicate my thoughts (connecting the dots, so to speak). As usual, I tend to draw a looping path rather than a straight line, hope this is clearer.

Having a difficult time with descriptions and details being offered. See screens in BOTH pvc pipes.

Going with what has been stated/offered by OP (and not, for example an HRV) that is a "furnace" terminal and a "water heater" terminal, and implied as both are gas fired applinces, as correct though...

Seems a fair "bet" that the deck surface is at first floor level.

Starting with finished ground level, noting proximities, obstructions, known condensate issues, screened terminals, and termination area and equipment, materials, subject to deteriortion, hazard, etc. to undilluted trapped, further collected, caught, vented products, corrosive and noxious and region weather/condensation venting issues.

Mike Lamb: See 12.9.2 and 12.9.4 in addition to 12.9.6 of 2012 NFPA 54.

Comparing a DV fireplace appliance/accessory to a condensing or semi-condensing (by design or by circumstance of installation & operating conditions) furnace isn't really valid.

Either that deck is cover to a walk-out below or its finished ground surface. Looks like thats apartments or multi-family housing multiple buildings parking lot other side of the fence.

Key here, is this is NOT according to the OP direct vent and sidewall termination, questionable whether the materials employed are in fact correct for the mfg and the jurisdictional restrictions, and yep now gotta leap to assumptions as Asked OP and OP didn't answer ?s - gotta assume here (by visual clues i.e. fence height, etc.) and limited descriptions from the topic discussion originator...and non-responsiveness from OP as to full-basement utility area, half-basement utility area, or crawl space utility area, elevations questions, etc. assuming the "deck" IS the FINISHED GROUND LEVEL (since as i recall the fence restrictions in the area tend to averge five or six feet high limitations side yards, even mixed residential zoning. I'd throw weak odds it might even be somewhere near or along the Des Plaines Rvr. flood zones from the generalized 'look' of things new & old in the pics.

The mechanical draft terminal(s) MUST be at least a foot (and in Chicago area higher) ABOVE that occupied deck surface, and either four feet below OR four feet horizontally aside that operable window opening for condensing.

The OP has stated repeatedly the terminal for the "furnace" is NOT for a Direct Vent application. He has identified the appliances as a "Furnace" and a "Water Heater" and has indicated both SCREENED PVC or CPVC projections are individual appliance vent terminations. Not vested in the representations vague as they may be, but taking at face value. furthermore, there has been no mention of any fireplace, decorative, or accessory by the OP. Only a "furnace" and a "water heater" of unknown description, neither of which is "direct vented".

When the mfg refers to the Nationl Fuel Gas Code, ANSI standard number, etc. it would correspond to the edition in effect at the time the appliance was manufactured. Despite what older applince instructions may hve said regarding Plexi vent and other materials "in vogue" at the time of manufacture - such materials and many of the quick fixes employed by various settlement contractors are not necessarily correct or okay, and one reason why many such vintage applince mnufacturers have desite branded names still bandied about, engaged in ownership swaps, structured sales, etc. for distancing. I do not believe corporate structure or ownership of any entity in such appliance mfg of those vintges remains identical as to "pockets" post settlements and court actions regarding same. Still not a HINT as to the age of the equipment pondered in the op.


NFPA 54 definitions:

3.3.99.7.2 Mechnical Draft Venting System. A venting system designed to remove flue or vent gases by mechnical means, which can consist of an induced draft portion under nonpositive static pressure or a forced draft portion under positive static pressure.

3.3.99.7.1 Forced Mechnical Draft Venting System. A venting system in which a fan or other mechnical device is used to cause the flow of flue or vent gases under positive vent pressure.

3.3.52.1 Mechanical Draft. Draft produced by a fan or an air or stream jet. When a fan is located so as to push the flue gases through the chimney or vent, the draft is forced. When the fan is located so as to pull the flue gases through the chimney or vent, the draft is induced.

3.3.17.5 Power Burner. A burner in which either gas or air, or both, are supplied at a pressure exceeding, for gas, the line pressure, and for air, atmospheric pressure; this added pressure being applied at the burner. A burner for which air for combustion is supplied by a fan ahead of the appliance is commonly designated as a forced-draft burner.

3.3.17.5.1 Fan-Assisted Power Burner. A burner that uses either induced or forced draft.

3.3.6.11 Vented Appliance.

3.3.6.11.1* Category I Vented Appliance. An appliance that operates with nonpositive vent static pressure and with a vent gas temperature that avoids excessive condensate production in the vent.

3.3.6.11.2 Category II Vented Appliance. An appliance that operates with a nonpositive vent static pressure and with a vent gas temperature that can cause excessive condensate production in the vent.

3.3.6.11.3 Category III Vented Appliance. An appliance that operates with positive vent static pressure and with a vent gas temperture that avoids excessive condensate production in the vent.

3.3.6.11.4 Category IV Vented Appliance. An appliance that operates with a positive vent static pressure and with a vent gas temperture that can cause excessive condensate production in the vent.

Now, the "finished ground level" reference plane here where the (uncovered, i.e. not refered to as porch, portico, etc.) and occupied "deck" surface adjoins the building at the exterior wall.

The vent terminals are below this reference plane ("finished ground level" at this adjoinment to the building exterior wall) and are required to be at least one foot above same (plus in NE Illinois av. snow depth).

Furthermore, the terminal(s) are neither four ft below, nor four ft horizontally from the pictured operable window opening pictured above the deck surface.

A AmSt/Trane Cat. IV DV (X or Y in a model number cell), sealed combustion chamber) with alternate non-DV installation is not identified. A "C" (condensing, not necessarily a Cat IV), non-sealed combustion chamber, has been illuded to ("C" in model number cell). Not sold on the description vs. model number & mfg. or appliances' type identification either ('just sayin').

The horizontal plane finished structure/building deck surface is occupied space.

The "finished ground level" adjoining the building at THE exterior wall and the "through-the-wall" vent terminal(s) pictured IS apparently, the top of the "deck" surface.

Chicago area is known (local experience) is that condenstion CAN BE a problem, even in venting systems serving designed as Category I and Category III appliances. Examples from HIs in the region have even been posted most recently, for example condensation/ice formation at exposed B-Vent extensions from roof decks, condensation ice from wall terminals.

Adjacent buildings and structures. Projections, cover, deck structure itself projections from vertical and horizontal planes. The decking material itself and the decking structure shown obstructs the vent terminal openings.

The vent terminal openings are not above the "finished ground level" reference plane at the adjoinment of same (deck surface) to the building at this exterior wall location.

It appears that this deck surface extends to within six feet of the lot line, or fence line (i.e. less than six feet from building to fence/lot-line).

The terminals pictured do not appear to be 25 ft below the other pictured operable window, nor 2 ft above same either.

The OP has stated neither appliance terminal is for a Direct Vented appliance. The "C" indicates a condensing, non-direct vent (non-sealed combustion chamber) appliance if early 80s to 2008 Am St branded.

2012 NFPA 54 references.

12.4.3 Mechanical Draft Systems.

12.4.3.1 Mechanical draft systems shall be listed and installed in accordance with both the applince and the mechanical draft system manufacturer's installation instructions.

12.4.3.2 Appliances requiring venting shall be permitted to be vented by means of mechanical draft systems of either forced or induced draft design.
*
12.4.3.3 Forced draft systems and all portions of induced draft systems under positive pressure during opertion shall be designed and installed so as to prevent leakage of the flue or vent gasses into a building.

12.4.3.4 Vent connectors serving appliances vented by natural draft shall not be connected into any portion of mechanical draft systems operting under positive pressure.

12.4.3.5 Where a mechanical draft system is employed, provision shall be made to prevent the flow of gas to the main burners when the draft system is not performing so as to satisfy the operating requirements of the appliance for safe performance.

12.4.3.6 The exit terminals of mechanical draft systems shall be not less than 7 ft (2.1 m) above finished ground level where located adjcent to public walkways and shall be located as specified in 12.9.1 and 12.9.2

12.9* Through-the-Wall Vent Termination.

12.9.1 Mechanical draft venting system shall terminate at least 3 ft (0.9 m) above any forced air inlet located within 10 ft (3 m).
Exception No. 1: This provision shall not apply to the combustion air intake of a direct vent appliance.
Exception No. 2: This provision shall not apply to the separtion of the integral outdoor air inlet and flue gas discharge of listed outdoor appliances.

12.9.2 Mechanical draft venting system of other than direct vent type shall terminate at least 4 ft (1.2 m) below, 4 ft (1.2 m) horizontlly from, or 1 ft (300 mm) above any door, operable windows, or gravity air inlet into any building. The bottom of the vent terminal shall be located at least 12 in. (300 mm) above finished ground level.

The terminal is neither four feet below the window, nor four feet horizontally from the window, nor is above the window. The terminal is not at least 12" above the finished ground level (the deck topside surface) in fact is BELOW it (the finished ground level).

12.9.3 The vent terminal of a direct vent appliance with an input of 10,000 Btu/hr (3 kW) or less shall be located at least 6 in (150 mm) from any air opening into a building, an appliance with an input over 10,000 Btu/hr (3 kW) but not over 50,000 Btu/Hr (14.7 kW) shall be installed with 9 in (230 mm) vent termination clearnce, and an applince with an input over 50,000 Btu/Hr shall have at least a 12 in (300 mm) vent termination clearance. The bottom of the vent terminal and the air intake shall be located at least 12 in. (300 mm) above finished ground level.

12.9.4 Through-the-wall vents for Category II and Category IV appliances and noncategorized condensing appliances shall not terminate over public walkways or over an area where condensate or vapor could create a nusiance or hazard or could be detrimental to the operation of regulators, relief valves, or other equipment. Where local experience indictes that condensate is problem with Category I and Category III appliances, this provision shall also apply. Drains for condensate shall be installed in accordance with the appliance and vent manufacturer's installation instructions.

12.9.5 Where vents, including those for direct-vent appliances or combination air intake pipes, penetrate outside walls of buildings, the annular spaces around such penetrations shall be permanently sealed using approved materials to prevent entry of combustion products into the building.

12.9.6 Vent systems for Category IV appliances that terminate through an outside wall of building and discharge flue gases perpendicular to the adjacent wall shall be located not less than 10 ft (3 m) horizontally from an operable opening in an adjacent building.
Exception. This shall not apply to vent terminals that are 2 ft (0.6 m) or more above or 25 ft (7.6 m) or more below operable openings.

The deck joists and condensing trap wood box (hiding obstructed terminals and catching, likely so window screen doesn't disolve from corrosive condensate from WH in non-winter months) are projections defacto adjacent walls regarding proximity to vent terminals covered and obstructed by decking surface and further covered and restricted by wood structure "box" over deck surface "cut out" enclosing terminals.

HG, your answers are too long and meandering and I just stop reading after a few sentences. You are verbosity posing as help. I've moved on.

Mike Lamb: See 12.9.2 and 12.9.4 in addition to 12.9.6 of 2012 NFPA 54.'Happy trails' and 'bless your ... heart'.

Originally Posted by H.G. Watson, Sr.

Mike Lamb: See 12.9.2 and 12.9.4 in addition to 12.9.6 of 2012 NFPA 54.'Happy trails' and 'bless your ... heart'.

Thank you.

"Comparing a DV fireplace appliance/accessory to a condensing or semi-condensing (by design or by circumstance of installation & operating conditions) furnace isn't really valid."

Sigh.... Watson, do you understand that the type of venting and combustion efficiency are two totally separate issues? The question I addressed was to your assertion that DV=condensing. It does not by default. A CAT IV furnace or boiler firing with room air will condense. A direct vent water heater vented right out a wall usually will not condense. Most gas fireplaces now are direct vent meaning sealed combustion yet they are under 83% AFUE meaning they don't condense so yes, fireplaces were relevant to the discussion for those who read and comprehend.

I think part of the problem is many people use the term "direct vent" when discussing power vented water heaters. Direct vent means two pipes--either co-axial or co-linear.
In that tome you posted there is some good info. but as Mike said you spackled over it with too much fluff.

Originally Posted by Bob Harper

"Comparing a DV fireplace appliance/accessory to a condensing or semi-condensing (by design or by circumstance of installation & operating conditions) furnace isn't really valid."

Sigh.... Watson, do you understand that the type of venting and combustion efficiency are two totally separate issues? The question I addressed was to your assertion that DV=condensing. It does not by default. A CAT IV furnace or boiler firing with room air will condense. A direct vent water heater vented right out a wall usually will not condense. Most gas fireplaces now are direct vent meaning sealed combustion yet they are under 83% AFUE meaning they don't condense so yes, fireplaces were relevant to the discussion for those who read and comprehend.

I think part of the problem is many people use the term "direct vent" when discussing power vented water heaters. Direct vent means two pipes--either co-axial or co-linear.
In that tome you posted there is some good info. but as Mike said you spackled over it with too much fluff.

Sigh. The subject under discussion was a residential gas furnace - not 'fireplace' not 'water heater. Standards, efficiency, venting of furnace, incorrectly identified, and the specifics acceptable for same FURNACE, not DV application installation. Not a fireplace, and certainly not a Direct Vented fireplace!

The OP asserted operable window proximity wasn't of issue. Of course the storm/screened window proximity would be of issue since the clearance is four feet below or four feet horizontally from if not one foot above same (and the pictures show same clearance is not met). This is also relayed in Table 10 (non-direct vent, U.S. clearances) right column in the page referenced later by the OP regarding the Trane and American STandard branded model rev. 2009 instructions later posted, the same restrictions referenced in NFPA 54 at the subsections I posted from 2012.

No Bob, the OP provided an incomplete and incorrect model number for a branded American Standard Gas Furnace. The Model Number Cell area with a "C" that the OP provided, I explained, would indicate a CONDENSING Furnace, and not primarily designed as DV. I questioned the accuracy and completeness of the model number provided by the OP from the get-go. I provided example and links as to the formating of Am St & Trane furnaces.

The OP relayed the installation was not DV. A 2-pipe installation is not necessarily a Direct Vent installation either.

The furnace in question is not being direct vented - according to the OP. The previously mis-identified (incorrect model number format) furnace - was designed as a DV (alternative applications and installations permitted) AND designed primarily as a Cat IV furnace - AND to be functioning as a CONDENSING furnace ("C"). When installed within the manufacturer's instructions for alternate installtion methods OTHER than DV and even when sourcing combustion air from outside but not as true DV (such as through the roof venting) the efficiency can be driven down to below 83% and thus - no longer functioning as a Cat IV furnace (17% or less stack loss).

Venting and combustion efficency are not two totally independant issues. Altering the parameters of the first can and often does effect the later, esp. with non modulating single stage in harsher climate zones than your own.

The higher effiency sticker rating for DV application vs. alternative installation venting option applications and lower end mid-efficency performance.

Although I agree with the essence of the opening of your second-to-last paragraph, the OP did not indicate a gas-fired storage type "water heater", point being - I don't recall the word "tank" or for that matter "tank-less" ever having been mentioned by the OP.

In summary, all two-pipe installations are not DV, efficencies of equipment primarily designed to be DV'd & Cat IV do not necessarily maintain their efficiency when alternatively installed/applied, a true DV installation is not necessarily "high efficiency" or Cat. IV, not only DV'd Cat IV furnaces produce condensate; and obstruction of vent terminal, restriction - to free air, is akin to a reduction.

Finally, yes, the standards for residential furnaces do come into play and this is where the distinctions with a difference apply in the categorization, efficency, sealed or non-sealed combustion chamber (true DV eligible), etc. apply.

Watson, do you hear the water dripping down from the walls of that well you're digging to China?