Should I run my clothes dryer during APS’ peak demand hours?

Q: I’ve been told I shouldn’t run my clothes dryer during APS’ peak demand hours. It’s a natural-gas dryer, so shouldn’t I be able to run it without the huge cost?

-- John Y., Sun City West

A: Hi John. The short answer (“TLDR” in modern parlance) is no. The air that any clothes dryer uses – gas or electric – is replaced with unconditioned air that comes from the attic, the outside, and/or the garage. (Ventless dryers excepted.)

The long answer:

Avoiding running an electric dryer during APS’ peak demand hours is an easy case to make. Running an electric clothes dryer on high – just once – for one hour from, say, 4 p.m. to 5 p.m. can add up to $100 to your electric bill! (Not a typo.)

Why? Because those on APS’ 4-7 With Demand Charge plan are hit with $16.875 *per kilowatt* of energy used in one hour during peak hours (4 p.m. to 7 p.m.). An extra-capacity dryer set to “high” uses upwards of 6 kWh – this can be more usage than even a 5-ton air-conditioning system.

But there’s more to the story. Clothes dryers are exhaust appliances; they move interior air across a heater, then across your clothes, then exhausts that hot, moist air outside. Many modern dryers move 250 cubic feet per minute, taking air from inside your home and spitting it outside.

Let that sink in. If the dryer is removing air from your home, the air has to be replaced. Where does that air come from?

(Cue dramatic music)

It comes from the attic.

In Phoenix.

In a 2,000-square-foot home with 8-foot ceilings, a dryer running for an hour moving 250 cfm will replace 94% of the air in the home. Most of that air will come from the attic.

Homeowners are encouraged to pre-cool their homes about an hour and a half before peak hours begin, and then coast through the peak hours without their air-conditioning running. Turning on the dryer undermines that.

This is why even gas dryers shouldn’t be used during peak hours.