What this article is
I'm a commercial HVAC service manager. I've been handling installations and replacement parts orders since 2014, and I've made enough expensive mistakes to fill a binder. This article answers the questions I keep hearing: AAON units, AAON heating parts P79990, electric heaters, that little Woozoo fan, and the real disadvantages of a heat pump.
Here's what people ask me most:
- Is an AAON HVAC unit worth the money?
- Can I just order the AAON heating parts P79990 and be done?
- Can an electric heater replace my heat pump?
- What are the disadvantages of a heat pump?
- Does a Woozoo fan fix a cold room?
Is an AAON HVAC unit worth the money?
I get that question from building owners at least twice a month. My honest answer? If the unit is the wrong size, no. If you actually need commercial-grade equipment and you plan to keep it for twenty years, yes. AAON builds for the commercial side of HVAC. The cabinets are stiffer, service access is better, and the controls are not locked down the way some budget brands lock them.
I didn't always think that way. In my first year as a service tech, I told an owner the premium brand was a waste of money. We later dealt with a budget unit that failed right after the warranty expired. The replacement was an AAON HVAC unit, and it's been boringly reliable ever since. I'll take boring.
That experience taught me to separate the machine from the installation. I've also seen expensive AAON equipment fail early because the startup technician skipped the checklist. No brand can save you from a careless startup.
What about AAON heating parts P79990?
So you searched 'AAON heating parts P79990.' That's a good first step, but don't stop there.
Look at the unit's data plate before you order. P79990 may be the heater assembly in the parts diagram, but the diagram only matters if the unit voltage and production date match the supplier's cross-reference. Most parts sites will happily show you a photo and a Buy button. What they won't show you is whether the terminal lugs are identical or whether the factory superseded that part to a newer revision.
I learned this in 2022 when I ordered a cheaper 'fits AAON' heater from a distributor. It looked exactly like the failed part. Same shape, same size. The terminal lugs were half an inch too close together. It would have required modifying a high-voltage heater to make it connect. I returned it and ordered the factory replacement. Paid more, waited longer, learned my lesson.
Don't repeat my mistake. Use the model number and serial number, not just the part number. Genuine is not always mandatory, but verified is.
Can an electric heater replace my heat pump?
Here's the short answer: no.
A portable electric heater is fine for emergency heat in one room. It is not a replacement for a heating system. Resistance heating is 100 percent efficient in the narrow sense that all the electricity becomes heat, but one kilowatt still produces about 3,412 Btu/h. A heat pump can use that same kWh and move two or three times more heat into the building.
According to the U.S. Department of Energy's Heat Pump Systems page (accessed April 2025), an air-source heat pump can deliver two to three times more heat energy than the electricity it consumes. That gap shows up on your electric bill.
Use the electric heater while you're waiting for a repair. Keep the thermostat at a safe temperature and don't give frozen pipes a chance. But the electric heater is a band-aid, not a solution.
Okay, what are the disadvantages of a heat pump?
Straight talk? A heat pump has tradeoffs. Here are the ones I see in the field.
- Cold weather output drops. Air-source heat pumps absorb heat from outdoor air. When the temperature goes down, the heat source has less energy to give. Modern cold-climate models are much better than older ones, but output still falls. At some point auxiliary heat has to pick up the load.
- Defrost cycles are not invisible. The outdoor coil ices up in humid cold conditions. The unit has to reverse into defrost. You will hear the change, and you may feel a cooler draft indoors. It's normal, but it's a disadvantage.
- Installation quality is the whole game. A heat pump is a refrigeration system, an airflow system, and a control system. Screw up one and the efficiency collapses. Most bad heat pump reviews trace back to installation quality.
- Your local energy costs decide the payback. Where natural gas is cheap and electricity is expensive, a gas furnace may still be cheaper to operate. That doesn't make heat pumps bad. It makes the math local.
Some disadvantages are less relevant for water-source heat pumps. Those units exchange heat with a water loop, so they don't depend on outdoor air temperature the same way. Many AAON units are water-source models. They avoid some cold-air problems, but they bring water treatment and loop maintenance into the picture. Every option has a tradeoff.
I'm writing this in April 2025. Cold-climate heat pump technology has moved fast since 2020, and it will keep moving. The fundamentals haven't changed, but the execution has transformed. If someone tells you heat pumps have zero downsides, treat that as a red flag.
Does a Woozoo fan help with HVAC problems?
Short answer: sometimes.
The Woozoo fan is a decent little air circulator. It won't heat your house, and it won't replace a blower on a commercial unit. What it can do is mix air in a single room. Warm air rises; cold air sits at the floor. A small fan running on low will make the temperature more even and reduce the cold spot near the window.
If you're running an electric heater because the heat pump is down, a fan is a no-brainer. It spreads the heat around the occupied space. But if the cold room is caused by an AAON HVAC unit with a dirty filter or a zone damper problem, the fan is just covering up the symptom. Fix the unit first, then use the fan as a bonus.
