What is an air handler, and do I have one? An air handler is the indoor blower unit for a heating and cooling system that doesn’t burn fuel — it contains a blower, an evaporator coil, and usually electric heat strips. Here’s the short version of whether you have one: if you have a gas furnace, you don’t have an air handler. The two are different boxes doing different jobs, and your house has one or the other. If your indoor unit has no gas line and no flue pipe, it’s an air handler.
The 30-second test
Go stand in front of your indoor unit — basement, closet, attic, garage, wherever it lives. Ask two questions.
- Is there a gas line running into it? Usually a black iron pipe with a shutoff valve.
- Is there a pipe leaving the unit and going up and out of the house? Metal or white PVC. That’s a flue, and it exists to carry combustion gases outside.
If either answer is yes, you have a furnace — something burns in there. If there’s no gas line and no flue, and the only things entering the cabinet are electrical conduit and refrigerant lines, you have an air handler.
What’s actually inside an air handler
Three things:
A blower. The fan that moves air through your ducts, in both seasons.
An evaporator coil. The cooling side — the same component any central AC has indoors.
Electric heat strips. Resistance elements, functionally similar to what’s inside a toaster. Not every air handler has them, but most in our climate do.
What it does is move air. It doesn’t create heat by burning anything. Your heat comes from somewhere else — usually a heat pump outside, which moves heat from the outdoor air into your house, even when it’s cold out.
What an air handler doesn’t have
This list matters more than the first one:
- No burners
- No heat exchanger — so nothing to crack
- No flame sensor
- No gas valve
- No flue
- No carbon monoxide risk from this unit
We’ll be straight about what that means: an air handler is a simpler and safer piece of equipment than a gas furnace. Everything we write about cracked heat exchangers and combustion safety simply doesn’t apply to it. If you have an air handler, you need us less often than your neighbor with a furnace does.
What it does need is airflow and electrical attention: filter changes, blower cleaning, checking the heat strip elements and contactors, and coil condition — plus the refrigerant side, which belongs to the heat pump.
The “emergency heat” button costs you money
This is the part most heat pump owners have never been told.
Your thermostat probably has a setting labeled Emergency Heat, Em Heat, or Aux. It is not a boost button. It does not mean “hurry up.”
What it actually does is shut off your heat pump — the efficient part — and run nothing but the electric heat strips. Strip heat is resistance heat, the most expensive way there is to heat a house. Running emergency heat when you didn’t need to can add real money to a single winter bill.
Use it in one situation: your heat pump has genuinely failed and you need heat tonight. It’s a backup, not a boost.
And if aux or emergency heat comes on by itself on a day that isn’t especially cold, that’s a symptom. Your heat pump isn’t keeping up, and it’s quietly costing you money every hour it runs. Worth a service call.
Dual fuel: when you have both
A lot of homes in our area are dual fuel — a heat pump outside and a gas furnace inside. Those homeowners genuinely have both pieces of equipment.
In that setup, the heat pump handles mild weather and the furnace takes over when it gets truly cold. The temperature where that handoff happens is a setting, and it’s one we configure. If you have both and you’ve never asked where your changeover point is, it’s worth asking — it’s the difference between running the efficient half and the expensive half.
Related questions
Is an air handler the same as a furnace? No. A furnace burns fuel to create heat and has a heat exchanger and a flue. An air handler has no combustion at all — it moves air and usually contains electric heat strips. A home has one or the other.
Do I need an air handler if I have a heat pump? Yes. A heat pump needs an indoor unit to move air through the house. That’s either an air handler, or in a dual-fuel setup, a furnace.
Does an air handler produce carbon monoxide? No. Carbon monoxide comes from combustion, and an air handler doesn’t burn anything. If your home has any other gas appliance — water heater, range, fireplace — you still want CO detectors.
What is the emergency heat setting on my thermostat? It shuts off the heat pump and runs only the electric heat strips. It’s the most expensive way to heat your home and should only be used if the heat pump has failed.
Why does my air handler run but the house isn’t warming up? Common causes are a failed heat pump outdoors, a failed strip heat contactor, or a system stuck in defrost. The blower can run normally while the heat source isn’t working.
Next step
If you’re not sure what you have, or your aux heat is running more than it should, we’ll take a look and tell you plainly what’s going on. Schraer Heating & Air Conditioning, serving the St. Louis Westplex since 1946 — Warren, Montgomery, St. Charles, Lincoln, Franklin, and St. Louis Counties. Schedule service or call 636-200-3276.
636-200-3276