Thread: clothes dryer makeup air

How should I interpret this:

G2439.4 (614.5) Makeup air. Installations exhausting more than 200 cfm (0.09 m3/s) shall be provided with makeup air. Where a closet is designed for the installation of a clothes dryer, an opening having an area of not less than 100 square inches (0.0645 m2) for makeup air shall be provided in the closet enclosure, or makeup air shall be provided by other approved means.

Is this saying that there must be makeup air provided if a clothes dryer is in a closet, regardless of the 200 cfm limitation? There's no dryer, so I don't know what the cfm is.

And, when does a laundry room become a "closet"? There is room for full size washer and (gas) dryer and a typical laundry tub.

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I do call out for make-up air if a gas dryer is present (they may install an electric dryer).
I do it on a case by case basis; usually if the closet or a small room I call it out.

Of course, just last week I had a realtor state "oh, they'll probably just leave the door open when doing laundry".

Originally Posted by Darren Miller

I do call out for make-up air if a gas dryer is present (they may install an electric dryer).
I do it on a case by case basis; usually if the closet or a small room I call it out.

Of course, just last week I had a realtor state "oh, they'll probably just leave the door open when doing laundry".

You seem to be confused between: "combustion & dillution air" vs.
make-up air"; and "exhausting" (ventillation/balanced air-exchange, removal of odors, moisture ladden air, for the maintanance of fresh breathable air) vs. "venting" (combustion products).

Make-up air (sufficient) is required (infiltration, natural/gravity or mechanically supplied/ventillated) for dryers that exhaust, or any exhausting is taking place from occupied space.

Both gas-fired and electric clothes dryers REQUIRE make-up air; both require ducts to EXHAUST (mechanically) and therefore require a means to supply/replace that air to be exhausted.

If you keep in mind that any exhausting clothes dryer is a big exhaust fan (that if fuel-fired also must vent combustion products) it is easier to follow.

The exception (for an exhaust duct, and therefore provisions for "make-up" air) is for a LISTED Condensing clothes dryer being PRESENT. Condesing clothes dryers do not exhaust (expell to the out-of-doors) water vapor ladden air which is sourced (taken in) from the space from which it is located.

M1502.4.6 Exhaust duct required. Where space for a clothes dryer is provided, an exhaust duct system shall be installed. Where the clothes dryer is not installed at the time of occupancy the exhaust duct shall be capped or plugged in the space in which it originates and identified and marked "future use."

Exception: Where a listed condensing clothes dryer is installed prior to occupancy of the structure.

Consult Section G2403 if you're having trouble (General Definitions for the Gas section), Subsection G2438.1 (604.1) General, and Section G2407 (304) COMBUSTION, VENTILATION AND DILUTION AIR (regarding how to calculate and/or accomplish).

It contains much, including the following:

AIR, EXHAUST. Air being removed from any space or piece of equipment or appliance and conveyed directly to the atmosphere by means of openings or ducts.

AIR-HANDLING UNIT. A blower or fan used for the purpose of distributing supply air to a room, space or area.

AIR, MAKEUP. Air that is provided to replace air being exhausted.


G2438.1 (613.1) General. Clothes dryers shall be tested in accordance with ANSI Z21.5.1 and shall be installed in accordance with the manufacturer's installation instruction

Here's a free link to the entire G2407 (304) COMBUSTION, VENTILATION AND DILUTION AIR section (clickable link, scroll down on page): Chapter 24 - Fuel Gas

HTH.

Perhaps this is a subject more for a home energy forum than a home inspection one, and it may be a bit of a hijack, but I do find it an interesting one about appliances that exhaust ‘raw’ air from a home and I’m wondering what solutions people are seeing out there?

In our area new home construction is getting tighter and tighter, blower door test of < 1.0 air exchanges per hour are being achieved more and more. Indoor air quality is maintained with HVRs or air-to-air heat exchangers, targeting 1.5 – 2.0 exchanges per hr.

But what about those items (e.g. clothes dryers) that exhaust directly? And in particular also kitchen exhaust hoods? Some of the higher grade ones pull 500 – 750 cfm!

The issue of bathroom ventilation has largely been addressed by ducting them through the HVR with no local in the bathroom fan. The wall switch (or timer) triggers the HVR or air-to-air remotely.

But such is not possible with kitchen exhaust due to the grease laden air issue. We see now where a relay is required to trigger the HVR when the kitchen exhaust is started (still ducted directly out however), and that’s some make up air, but even then it’s still not really correct because the HVR is designed to be 1:1 inflow/outflow cfm and the kitchen exhausting hood running upsets that. I.e. the HVR ends up with more cfm flowing inbound than outbound, lowering its efficiency.

And it still leaves the issue of clothes dryers which are left to just create a negative pressure unbalance in the home. I’m not sure what the cfm exhaust is of your average clothes dryer is but I suspect it’s got to be in the several 1000.

So what solutions toward achieving truly equal inbound/outbound air flow balance, and still being able to cook and dry clothes, are popping up out there?

A clothes dryer on average pulls 200 cfm of air. A fireplace 300 cfm. I've been in tight houses and turned on all fans including a large range hood and dryer. It does pull negative air but not that negative. I've seen worse in a leaky house with all the bedroom doors shut and the good amount of supply leaks. Even the tighter new homes built here to the 2009 IECC are testing out with plenty of leaks for the dryers and bath fans.