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I just bought a house with a relatively two-year old A/C unit (installed 2018) and a natural gas furnace connected to central air. I'm interested in using the A/C unit as to heat the air in lieu of natural gas, but there are a few questions I'm stuck on before I can proceed.

  1. How can I know if it has a heat pump? (i.e., if the heat pump in the A/C unit can be reverse to heat the house?)
  2. If it has a heat pump, what do I need to do other than hooking it up to the thermostat?
  3. If it doesn't have a heat pump, can I make it into one with a retrofit?

I'm hoping for a generic answer to benefit the community, since specific versions of this question have already been asked. But if it helps, I live in Dallas, Texas. 

A/C: American Standard 4A7A6048J1000AA
Furnace: American Standard AUD1C080A9H41BC
Coil: 4TXCC009DS3HCAA
Thermostat: Nest (formerly an ACONT624AS42DA)

Update: I hope I didn't leave the impression that I'm set on using a heat pump instead of a furnace. Naturally, the question that goes side-by-side with this is, how can I project the relative costs of using the A/C as a heat pump versus a natural gas furnace. I figured that question would be more appropriate for a different thread.

Merchako
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    As someone that lives in Dallas, had a heat pump, and now has a gas furnace - the gas will be cheaper. Electric heat is terribly expensive, but gas heat isn't bad. – JPhi1618 Feb 06 '20 at 16:44
  • The issue with gas furnaces in Dallas is probably going to be the furnace being *too big* for the house heat loads, because they simply don't make small enough furnaces.... – ThreePhaseEel Feb 07 '20 at 02:19
  • [Is transitioning to all electric heating smart?](https://diy.stackexchange.com/questions/72795/is-transitioning-to-all-electric-heating-smart) – Mazura Feb 08 '20 at 03:02
  • [What are my options for heating an energy efficient home with low heating needs?](https://diy.stackexchange.com/questions/104795/what-are-my-options-for-heating-an-energy-efficient-home-with-low-heating-needs) – Mazura Feb 08 '20 at 03:03

2 Answers2

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In theory, yes, you could repurpose an A/C unit to be a heat pump but that's not a good choice. In order to switch between A/C mode and heating mode, you would have to re-plumb the lines every time you switched between heating and cooling or fashion some sort of reversing valve mechanism of your own design to accommodate this. The American Standard 4A7A6048J1000AA is NOT going to have a heating mode since this installation also has a gas furnace and the extra cost to put in a heat pump where it's not needed is just wasted money. Retrofitting is going to be a complete custom job and you're pretty much on your own doing something like this.

Not only that but it's going to be extraordinarily inefficient since the unit is designed as an A/C not as a reversible heat pump system.

The best choice, in my opinion, is to use your installation as designed, the A/C unit for cooling and the gas powered furnace for heating. Gas heating, especially in TX, is going to be significantly less expensive for heating and electric powered heating.

If you are set on eliminating the need for gas, the best approach is to replace the A/C unit with a heat pump system that would efficiently perform both heating and cooling.

jwh20
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  • I agree, and try to install the most efficient systems I can find, but we need to understand where our electricity comes from. A majority is from coal and natural gas powered generation. With natural gas being cheaper I usually lean that way as it ends up being cleaner than electricity from a coal fired power plant. – Ed Beal Feb 06 '20 at 16:18
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Retrofitting an air conditioning unit to work as a heat pump is impractical. It can be done, but I don't know of any instance where it has.

A common configuration is using a gas furnace as back-up heat for a heat pump. In very cold areas, as the temperature lowers the heat pump outputs less heat (and will likely require defrost cycles which use power), just when the house needs more heat. Having gas backup heat allows one to switch to gas heat, and reduce wear and tear, and a loss of efficiency on the heat pump.

Normally, the thermostat needed will be a two stage thermostat, and there will be control circuitry to stop heat pump operation when the gas furnace is running. One may also want a thermostat which monitors the outside air temperature, to switch between heat pump and gas furnace.

One advantage of a gas back-up is that it requires less power than a heat pump, and can often be run on a generator during power outages.

The change over points for the heat pump and the gas furnace can be adjusted to reflect energy costs, as well as operational considerations. As an example, when I had an air-source heat pump, I would often stop using it when the outside temperature dropped below 35F, so that there would not be coil defrost cycles.

mongo
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    Not sure why you got the down vote, I agree not normally done the reversing valve and some new controls would be needed, not really feasible and natural gas will normally cost much less, if you are worried about carbon footprint, only a few % of our grid is solar/wind, a majority is coal /natural gas generation methods, so burning gas at the furnace eliminates all the transmission losses for the electrical and a smaller carbon footprint. – Ed Beal Feb 06 '20 at 16:12
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    Not the downvoter, but a heat pump compatible thermostat will be able to control "aux heat" or "emergency heat" which would be disabling the heat pump and only using secondary heat. A thermostat with "two stage" heating or cooling does a slightly different job. – JPhi1618 Feb 06 '20 at 16:47
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    Most two stage or more thermostats these days are heat pump compatible, but even if not relays can be used. However, good point. – mongo Feb 06 '20 at 18:18