Heat pump vs AC unit

docmattman

I was looking for a little advice. I'm ready to replace my VERY old AC unit. I'm considering a heat pump for the dual fuel aspect. We have oil heat here, so it's VERY expensive to heat in the winter time. I know the basics about the heat pump. It will use electric heat until the temperature gets to a certain point, then the oil heating system will kick in. This sounds ideal for me because of the cost of oil.

I was wondering though if there are any disadvantages to a heat pump, other than the cost of the unit being higher than the regular AC. Also, if the price for electricity goes up beyond the price of oil, will I be able to change a setting on the heat pump to turn it off and just use oil heat?

Thanks in advance for the advice!

Doc Holliday

I'm not very familiar with oil and how that'd be used in conjunction with a heat pump but a heat pump, from what I understand and I understand a little , uses the same refrigerant it uses to cool a space as it does to heat it. This refrigerant heating comes on first, electric (aka auxilary) comes on as it's needed so let's say the system has been running for ten minutes and it hasn't aquired the desired set point, the electric heat strips will kick in to assist.

I think that's right.

As for components, you'll have a reversing valve on a heat pump which will energize to allow the refrigerant to reverse it's flow, from heating to cooling mode. Sometimes these get stuck but the good news is sometimes all it takes is a slight tap to get it to work. Other times it needs replacing.

You'll have a defrost mode on a heat pump. This means that every so often as ice builds up on the outside evaporator coil during heating (when in cooling mode the evaporator coil would be the inside coil) the system will automatically reverse it's refrigerant flow so as to melt that ice. While this is happening your blower on the inside will cut off. I think that's right as well.

Also you'll be having two txvs, one inside and one outside. Not very common for those to fail but as with anything with more bells and whistles, it's just that much more that possibly could go wrong.

zootjeff

I have a dual fuel setup with natural gas backup.

DO IT. The heat pump will save you money. In my case, Heatpump heat is 4 times less than the cost of resistive heat, and half the cost of my 92 percent Gas furnace. I was amazed when I started researching it. It cost me $300 more to get a heatpump than it did to get an AC unit. Why more people don't do this is driving me nuts.. You will likley notice the defrost cycles as they will blow cold air for a bit (The heatpump switches into defrost every 45 minutes)


With oil as a backup heat, they historically run hotter, so you can't have a plastic drip pan on the AC coil. But you already have the problem if you already have AC. (just costs a little more)

BTU is BTU.. The same rated heatpump will have the same cooling power as the AC only unit.

You have to have a fancier thermostat to control both fuels. I have the vision pro 8000 and that would work in your case too.

You should totally get a heat pump instead of an AC unit...

I can set my thermostat to Heat and it will use the heatpump until 35 degrees outside, I can set it to cool, or I can set it to EM heat which will only use the gas. You can pick and choose. The HP will take longer to get the house warm in the winter. If you want a quick change in temp, you can just choose EM heat and it will fire the oil heater right up..

Totally worth it.

zootjeff

A 13 and 14 SEER Goodman heatpump system has 0 TXVs in the outdoor unit for heating.

The indoor TXV for cooling is optional and just raises the efficiency..

beenthere

If the thermostat you use is a dual fuel thermostat. Then you can easily change it to not use the heat pump for heating, if electric goes up too much.

For the most part, your electric would have to go up (or already be real high ) a lot for a heat pump to cost more from heat, then an oil furnace.

Rick09

Remember that since the compressor runs for 4 seasons it WILL wear out faster than if you had a separate A/C and heating system from what I understand. May require more maintenance/service visits.

Doc Holliday

Thanks. I'm not too familiar with heat pumps, we don't have maybe a total of two in all of Houston, one being at my sister's place.

In 11 years in this trade I have yet to install one.

zootjeff

I hope posts like this don't discourage you however.. think of all the wear and tear on your furnace that you're saving by using your heat pump. And if 1 goes out in the middle of january you probly rather have it be the heat pump. That's also why you spring for the 14 seer unit with a lifetime warranty on the compressor.
To me this is the equivalent of saying don't drive your car because it might wear out..

Rick09

I hope my post doesn't discourage you. I have a heat pump system installed in my house. It has its pros and cons just like every other setup. Was simply pointing out 1 con. That being said my system is currently 20 yrs old. Just recently started having compressor problems.

zootjeff

So I just ran the numbers for Huston.. Do you have any feeling of the gas and electric rates over there?

If I consider my house was in Huston (1900 sq feet 1972 ranch with loft), and I base it on the last 12 months weather performance from the Huston Airport..

If I use my utility rates:
$1.11 per therm for gas
$0.093 per KWh for electric

Total cost for heating per year with HP plus Gas Backup is $165
Total cost per year for pure 92% gas heat is $250
Total cost per year for pure baseboard electric heat $564
Total cost for HP plus Electric Backup is $196


Now in my area (Portland OR) We do much more heating during the year than Huston. I spend $607 per year on my 14 SEER HP + 92% Gas setup and I was spending $928 on pure 92% gas setup. So in my area heat pump makes a lot of sense $320/yr pays stuff off a lot faster..

In Huston, you are going to have the occasional 20 degree day in the winter and you'll have to use some kind of backup heat. So you'll need resistive or gas/oil backup heat anyway for those couple days a year. So you can't get by just installing a heatpump with no backup heat. That is probably why no one installs heat pumps there, because you're only saving $85 a year owning a heat pump. But with everyone freaking out about energy these days, I'd think you'd have some more people going after that 85 bucks a year..

zootjeff

What is your zip code?

Doc Holliday

My sister's heat pump system has electrical heat strips as well. Not certain the kw of it but it's there.

I don't think there's much of a market for heat pump here because (hypothetically speaking without knowing or running any numbers) it'd take over ten to fifteen years to see any return on the investment on the purchase. Granted working for an hvac company at the time my sister needed a new heat pump some 8 years ago, I got it installed for $2400 through my company and they still turned a profit, it just wasn't me who installed it. That's an excellent deal on a heat pump. Usually close to double that or so I've heard.

We hardly use heat at all. For instance, I was walking around in shorts and a tee shirt Christmas Day.

Granted it did snow a month earlier but was gone the next day.

We have a lot of naural gas, and that's relatively inexpensive.