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?

-- Jill, Sun City West

A: Hi Jill. 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! (This is not a typo.)

Why? Because for those on APS’ Time of Use charges $16.875 per kilowatt of energy used in one hour during peak hours (4 p.m. to 7 p.m.). A large dryer set to “high” uses upwards of 6,000 watts (averaging about 3,000 watts) – this can be more usage than even a 5-ton air-conditioning system.

But there’s more to the story. Most clothes dryers are exhaust appliances; they move interior air across a heater, then across your clothes, then exhaust the heated (and moist) air to the outside of the home. 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 the summer.

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 several degrees before peak hours start and coast through the peak hours in the hope that the temperature in their homes will creep up slowly enough that they can ride through the 3 peak hours without their air-conditioning having to kick on. The minute they run their dryer, though, they begin to pull hot (and dusty!) attic air into their home. This undermines the whole idea of pre-cooling. This is why even gas dryers shouldn’t be used during peak hours.