Question about details of makeup air code

[Ccallais]

Hi there,

I have searched quite a bit throughout this forum and others trying to find a quality answer for my client but to no avail.

His builder installed a Whirlpool vent hood with a CFM motor class of 400 CFM. Tag says 350 CFM on high.


House has the usual gas appliances (range, WH, furnace) but no makeup air. Normally I recommend makeup air in all new builds and indeed I usually see it, even with homes with no gas. But the builder is pushing back on this (they said it wasn't necessary because they have a Broan zb110 exhaust fan in the laundry...huuuh?) and am hoping to get a better understanding of what the requirement should be here.

The two areas of the IRC that appear to pertain to this are of course the M1503.6, Makeup air required "Where one or more gas...appliances...is located within a dwelling unit's air barrier, each exhaust system capable of exhausting in excess of 400 cubic feet per minute shall be...provided with makeup air..."

and the G2407.4, Makeup air provisions. "Where exhaust fans, clothes dryers and kitchen ventilation systems interfere with the operation of appliances, make up your shall be provided."

So I suppose my questions based on those two code snippets are, 1. Does the 400CFM motor class count or the 350CMF High count?, and 2. Regardless of #1, does operation of the vent hood or other exhaust systems interfere with operation of appliances?

And 3., What are yalls thoughts?

Thanks for the help.

 

[classicT]

The 400cfm motor class is still not in excess of 400cfm. Per the code (M1503.6), it has to be greater than 400cfm. That said, I would go by the 350cfm on the plate. Either way, it does not matter.

Sounds like your builder is following code, the minimum standard. Is that what I would want myself, probably not. But unless you have contract documents requiring something above code, your builder will most likely give you a change order with $$$ owed.

 

[mtlogcabin]

G2407.4 is the applicable code to determine if make up air is needed for the home. If the water heater and furnace are "B" vent type appliances, then there may be an interference with their operation depending on the size of the home and the amount of combustion air available in the home


G2407.5 (304.5) Indoor combustion air.
The required volume of indoor air shall be determined in accordance with Section G2407.5.1 or G2407.5.2, except that where the air infiltration rate is known to be less than 0.40 air changes per hour (ACH), Section G2407.5.2 shall be used. The total required volume shall be the sum of the required volume calculated for all appliances located within the space. Rooms communicating directly with the space in which the appliances are installed through openings not furnished with doors, and through combustion air openings sized and located in accordance with Section G2407.5.3, are considered to be part of the required volume.

G2407.5.1 (304.5.1) Standard method.
The minimum required volume shall be 50 cubic feet per 1,000 Btu/h (4.8 m3/kW) of the appliance input rating.

 

[Joe.B]

Make-up air (or lack there-of) is mostly ignored in my area. For a long time houses breathed, so a range fan, bathroom exhaust, or clothes dryer would work fine because there were plenty of places for air to get in. As energy codes have tightened up, so have the buildings. Builders are often resistant to change because they've been doing it this way for 30 years." I was explaining this to an owner-builder who was very diligent to follow his plans and to follow code, and technically everything is built correctly. At final I recommended he plan on cracking a window when he runs the range exhaust and he was a little confused. The only place air could come in was through the bathroom fan. I told him to go into the bathroom while I turn on the exhaust. He was able to see the water level in the toilet rise with the range exhaust one. Then I had him turn on the bathroom fan first, then I turn on the range exhaust. It started pulling air bubbles through the toilet trap. That was an unpleasant surprise for him.

 

[Mr. Inspector]

Make-up air (or lack there-of) is mostly ignored in my area. For a long time houses breathed, so a range fan, bathroom exhaust, or clothes dryer would work fine because there were plenty of places for air to get in. As energy codes have tightened up, so have the buildings. Builders are often resistant to change because they've been doing it this way for 30 years." I was explaining this to an owner-builder who was very diligent to follow his plans and to follow code, and technically everything is built correctly. At final I recommended he plan on cracking a window when he runs the range exhaust and he was a little confused. The only place air could come in was through the bathroom fan. I told him to go into the bathroom while I turn on the exhaust. He was able to see the water level in the toilet rise with the range exhaust one. Then I had him turn on the bathroom fan first, then I turn on the range exhaust. It started pulling air bubbles through the toilet trap. That was an unpleasant surprise for him.

Interesting way to test for makeup air.