Combustion air requirement

[scanchain]

I’m finishing my basement, and this question relates to the combustion air issue for my water heater and furnace in a utility room in the basement. According to the inspector, the county follows the combustion air requirement in IRC G2407.

The input BTUH of my water heater and furnace sum up to 100,000 BTUH. The utility room abuts a large indoor area with a volume of 10,000 cubic ft.

According to G2407.5.1, which states 50 cubic ft of indoor air is required per 1000 BTUH, the large indoor area can support 200,000 BTUH of combustion, provided I open sufficiently large vents from the utility room to the large indoor area (G2407.5.3.1).

However, the inspector says finished indoor air does not count. However, I couldn’t find anywhere in the IRC which clarifies what is indoor air.

 

[jbwilkins]

You will find different jurisdictions (even inspectors) interpret some codes differently if there's a gray area (which there are many)......

Personally, your interpretation is the way I understand that code, HOWEVER If that's his understanding of the code you may be better off making him happy vs. pushing back......

 

[TommyK]

Fan in a can is usually the solution.

 

[scanchain]

The figures G2407.5.3 and G2407.6.1 does seem to indicate what constitutes indoor air and outdoor air.

If I have to keep the inspector happy, I would have to add in those large ducts to bring in outside air. So much for insulating the basement.

 

[HoosierBuddy]

Just a random thought:

My furnace allowed for EITHER installation using PVC to pull in outside air OR without that.

I elected to run the PVC to bring in outside air, to keep the furnace from putting negative pressure on the heated space.

Just thought you might check to see if your furnace includes provisions for pulling combustion air in directly from the outside like mine. If so, perhaps that would help with your issue?

Long shot, I know.

Phil

 

[Showkey]

The furnace does not have outside air intake pipe ?

 

[rlitman]

... So much for insulating the basement.

You've got it all wrong. Assuming air goes out the flue (and it has to, or safety cutoffs will hopefully prevent your death), then makeup air has to come from somewhere. Either you allow the fresh air to enter as close to the combustion as possible (with a sealed combustion unit being ideal), or you're just allowing outside cold air to be sucked into the rest of your finished space.

 

[scanchain]

Just a random thought:

My furnace allowed for EITHER installation using PVC to pull in outside air OR without that.

I elected to run the PVC to bring in outside air, to keep the furnace from putting negative pressure on the heated space.

Just thought you might check to see if your furnace includes provisions for pulling combustion air in directly from the outside like mine. If so, perhaps that would help with your issue?

Long shot, I know.

Phil

My furnace is the Lennox SL280UHV. I just briefly scanned through the manual -- it does not appear to have provisions to pull in outside air.

 

[scanchain]

You've got it all wrong. Assuming air goes out the flue (and it has to, or safety cutoffs will hopefully prevent your death), then makeup air has to come from somewhere. Either you allow the fresh air to enter as close to the combustion as possible (with a sealed combustion unit being ideal), or you're just allowing outside cold air to be sucked into the rest of your finished space.

True. But if I install the vents for outside air, they are permanent in all seasons and there is air leakage even if the furnace is not running in summer.

 

[brewchief]

My furnace is the Lennox SL280UHV. I just briefly scanned through the manual -- it does not appear to have provisions to pull in outside air.

You are correct, that furnace doesn't have any provisions for outside air, few if any 80% furnaces do.


You would need combustion air for the water heater anyways unless you replaced it with a direct vent model, they are available but $$$
Sent from my SM-G965U using Tapatalk

 

[rlitman]

True. But if I install the vents for outside air, they are permanent in all seasons and there is air leakage even if the furnace is not running in summer.

Well, for passive leak limiting, what I did was open a hole in my wall, and place back to back vent hoods in it.

The outside hood had the flapper seal removed, and replaced with a fixed hardware cloth screen (to keep rodents out).

The inside hood which opens into my boiler room still has the flapper in place, so it allows air to flow in, but prevents the combustion air inlet opening from allowing air out. I hear it click shut every time the boiler shuts down, but I don't really hear it flapping on windy days. I could always tape a penny to the flapper if it spent too much time opened.

If you want to get more sophisticated, and if your vent stack has a mechanical damper (it probably does), you could buy a second mechanical damper and install it on the inlet pipe. Just be sure to have it interlock the fire control in series with the vent damper, so that the boiler will hold off until the damper is positively opened.

But that last option is only useful for the furnace alone. Since your water heater needs combustion air as well, I think that the passive solution is your best bet. Now if you had an indirect water heater (like me), then the damper could help a bit. Maybe I should consider that ...

 

[scanchain]

Despite all these discussions about additional outside air venting, I think my indoor air volume meets the required IRC G2407. The air volume abutting to the utility room is huge. The question is how to have a "discussion" with the inspector. If I "win" the argument for combustion air with him, he might give me a hard time with the electrical inspection.

 

[Jackfre]

This is a common problem and your inspector is correct. You can throw some dough at the current furnace in a fan in a can of my preferred unit the competing Tjernlund Combustion Air Enforcer. These will only work on a call for heat. Outdoor grilles are ok, but are open spilling cold air 24/7. How old is your furnace? You might consider an upgrade on the appliance to a properly sized high efficiency unit that can be direct vented and eliminate the CA issues in the space. Don't oversize the new furnace.

 

[brewchief]

In the past outside air was required only if the house was of unusually tight construction, that definition was pretty loose and almost any house built within the last 20 years would fit the definition that was given.

How old is the house?

Is there an outside air duct connected to the return duct? Here an outside air intake connected to the return with a small grill in the furnace room on the supply and a single pipe to the outside will satisfy the requirements.



Sent from my SM-G965U using Tapatalk

 

[75gmck25]

I am confused about why the inspector is looking at your existing furnace and water heater if all you are doing is finishing off your basement. Or were these systems replaced during the upgrade?

If the furnace and water heater met current code when built, and still meet that code, then it should be grandfathered if you have not modified either system. If it functioned before using inside air, and you have a vent that continues to allow that same volume of air to enter the utility room, you still have the same inside air source.

Bruce

 

[scanchain]

The house is 18 years old and the furnace was replaced in 2017.

 

[scanchain]

I am confused about why the inspector is looking at your existing furnace and water heater if all you are doing is finishing off your basement. Or were these systems replaced during the upgrade?

If the furnace and water heater met current code when built, and still meet that code, then it should be grandfathered if you have not modified either system. If it functioned before using inside air, and you have a vent that continues to allow that same volume of air to enter the utility room, you still have the same inside air source.

Bruce

I am not changing either system. The inspector's argument is that things change if I finish the basement, since the indoor air in a finished basement does not count toward satisfying the combustion air requirement.

 

[mustangacman]

You could put in an Aprilaire system that would only open when the furnace runs.https://www.aprilaire.com/whole-house-products/ventilation/model-8126X

 

[scanchain]

You could put in an Aprilaire system that would only open when the furnace runs.https://www.aprilaire.com/whole-house-products/ventilation/model-8126X

Interesting idea, though it looks like the product is intended to introduce fresh air into the heated space rather than the utility/HVAC room.

 

[Jackfre]

As the manufacturers rep I have been called out on many, many heating system problems. You never call the rep until it is a catastrophe. People look at a basement that is 30x40x8 and say they need no CA as they have plenty of unconfined space. The builder leaves and the first thing the owner does is drag a pile of 2x4's down the bulkhead and build a wall around the appliances. In one case the basement was filled to within 1-2' of the first floor. The inspector is taking care of you on this call, especially as you do not have sealed combustion appliances. It is unfortunate that a discussion of future plans wasn't had upon replacement of the old furnace.

Negative pressure issues are hard to call. The common one is up in Maine with an oil burner on a very cold night in a tight house. We have taken the technology of the thermos bottle and applied it to home construction. The boiler is running through the night and no doors or windows are or have been opened. The burner is digging a hole pressure wise and the flame goes to hell and boom, a no-heat. The tech goes out, opens the door and the problem is solved, temporarily. I tell the customer what is happening and they look at me like I have two heads, or perhaps only half of one.

 

[MattT]

I really don't understand why you're fighting this one. This isn't one of the ******** codes designed to stop morons winning Darwin Awards. Containing the make up air within the utility room is in your best interests. Sucking it in thru' the house and conditioning it before it goes up the flue will cost you money.

And you've been given plenty of options for limiting the venting to on demand if you're that concerned about venting the room 24/7.

If I "win" the argument for combustion air with him, he might give me a hard time with the electrical inspection.

You so much as fight this you'll be putting the inspector on notice that you're the type who wants to do everything half a$$ed.