Trane Heat Pump with Gas Backup

dolce873

Just got Trane XV18 heat pump and X8V2-C gas furnace installed and wondered what temp I should have the backup furnace kick on in the winter? In the Niagara Falls/Buffalo, NY area.

Hot_water_fan

That’s an impossible question for us to answer, but here are some things to consider:

1. your heat loss: sometimes, you may exceed the capacity of the heat pump, so you’ll need the backup. We don’t know your heat loss so we can’t tell you what temp that would be at. You may never exceed the heat pumps capacity, in which case this is unnecessary. 

2. Economic balance point: at some temps, one system may be cheaper than the other. For me, the heat pump is always cheaper. For others, the heat pump will never be. Most fall somewhere in between. The colder it gets, the more expensive a heat pump will be. As electricity prices and gas prices change frequently, this is a moving target that frankly might be a waste of time thinking too hard about. 

3. Duct capacity: the air leaving a heat pump will be at a lower temperature than a furnace. Therefore, on the coldest days, you might need the furnace to increase the supply air temp to provide enough heat for the same volume of air (CFM) even if the heat pump has enough capacity to otherwise heat the house. 

4. Demand flexibility: some places incentivize using less electricity during peak periods. This would be a great time to use the furnace, especially if the utility is paying you decently. 

5. Overall efficiency/emissions: generally, heat pumps pollute less because using gas to power them is more efficient than burning gas directly, especially in a low efficiency furnace like that Trane. If that’s important to you, try to use the heat pump more. 

The simplest solution is trial and error, all you’re doing is pushing a button, so if you want to change something it’s not a big deal. Maybe try 20F to start and go from there. 

dolce873

Ok thank you for your detailed response, I really appreciate it!

Hot_water_fan

If you're interested in #2, post a redacted gas and electric bill and we can show you the calculations to use. They're simple once you have the prices available.

WMno57

6. Use it or Lose it. I'd run it at least once every two weeks regardless of the outdoor temp. No, you don't need to run it in the summer. It can sit all summer, and your furnace professional can deal with any fall start up issues. When you rest, you rust.

EdTheHeaterMan

or just pick a random number like 27°F and see if that works for you.

If it don't then change it.

dolce873

Thanks everyone!

EdTheHeaterMan

American Standard and TRANE are made in the same factory and often have identical equipment with a small change to the part number. I was an American Standard dealer when TRANE and Am Std came out with the variable speed equipment. They have a proprietary communicating thermostat that lets the compressor and fans and gas valves know what speed that they should operate. Very sophisticated piece of equipment. I believe that the thermostat will make that change automatically if you do nothing. However there is a setting that will override the outdoor temperature at which the changeover takes place. If you have access to that setting, I would try a random number at or below freezing (like 27°F) and see if that works for you. If you feel uncomfortable at that outdoor temperature, inside your home (and not because your wife is making you uncomfortable because you forgot St. Valentine's day) Then change the setting up a little and see if that makes a difference. Let it set in for a few days before you make another change. Eventually you will find the sweet spot.