Why your Prescott heat pump runs up a January electric bill.

The short version

An air-source heat pump moves heat rather than making it, which is why it is so efficient. But its capacity falls as the outdoor temperature drops, exactly when you need the most. Below a certain point — the balance point — it can no longer keep up on its own, and the system energizes auxiliary electric resistance heat to make up the difference.

Electric strip heat is essentially a very large toaster. It works, it is reliable, and it is the most expensive way to heat a house in Arizona. If your balance point is set too high, or the heat pump was undersized for the heating load, the strips run far more than they should and the bill reflects it.

Why Prescott specifically

Prescott sits at about 5,300 feet. It drops below freezing on roughly a hundred nights a year and its summers top out in the mid-80s. An hour west, Kingman sits at 3,300 feet and spends July above 105°.

Those are two different engineering problems, and a lot of equipment up here was sized as though it were the first one. Size a system off the summer cooling load in a climate whose real demand is winter heating, and you get a machine that short-cycles in July and leans on strip heat in January. That is the whole story on most of the bills we get called about.

Altitude makes it worse

Air at 5,300 feet is roughly 17% less dense than at sea level. A blower moving the same volume is moving less mass, so it carries less heat. Gas-fired equipment needs a derate the manufacturer publishes and plenty of installers skip. Neither effect is dramatic on its own; together, on a system that was already sized optimistically, they are the difference between comfortable and supplementing.

What we actually check

• Whether the strips are running when they shouldn't. A failed outdoor sensor, a mis-wired thermostat, or an emergency-heat switch left on will run resistance heat continuously while the heat pump sits idle. This is common, and it is cheap to fix.
• The defrost cycle. A heat pump in Prescott will frost its outdoor coil and needs to reverse periodically to shed it. A defrost board or sensor that has failed leaves the unit iced, capacity collapses, and the strips carry the house.
• The balance point and thermostat staging. Many thermostats will bring on auxiliary heat simply because the setpoint moved more than a couple of degrees. Turning the heat up six degrees at 6 a.m. is an expensive habit with a heat pump; a setback of one or two degrees is not.
• The actual load. We run a Manual J on the house at its real elevation, with its real insulation and its real window area — not a rule of thumb per square foot.

If the answer is new equipment

Sometimes the sizing is simply wrong and no adjustment fixes it. If that is where you land, the options worth asking about in this climate are a cold-climate heat pump, which holds far more of its capacity at low outdoor temperatures than the standard equipment most Prescott homes have, or a dual-fuel system that pairs a heat pump with a gas furnace and switches over when the heat pump stops being the cheaper way to make heat.

Both cost more up front than a like-for-like swap and both change the January bill permanently. Financing is available at 0% APR on approved credit through our third-party lender, which is worth asking about before you decide the right answer is another undersized unit.

Where we work up here

We run the Yavapai side out of Kingman and cover Prescott, Prescott Valley, Chino Valley, Seligman and Ash Fork. Call (928) 565-6440 or see what a residential install involves.