C5Phil

Your LP furnace is a Carrier Infinity furnace?

What mdl evap coil?

What size furnace and HP.

With rates like that, I am surprised you did not go all electric.

Your dealer should have prepared an analysis of where the temperature balance point would be.

If he didn't, you should ask him to. I assume you know how to adjust the temperature setting for switchover between HP and gas backup. If you don't, you need to find out how to do this.

I would set the changeover at 25 deg fah to begin with and adjust up and down based on your comfort and whether the HP is maintaining your thermostat setting. Obviously, you want to go as low as possible to stay off the more expensive LP heat.

That's the best advice I can offer.

Keep in mind the balance point I refer to is different for every home depending on HVAC and home's building envelope/insulation qualities.

IMO

tigerdunes.. thanks for the advice-- yes my back up furnace is an infinity 98% eff. My dealer set the lock out at 35 degrees-- this was Carriers first install of this new HP in my area and I think they are just playing it real safe so I don't have any problems... my dealer says I can play around with it - he showed me how to change it- I'm just wondering how low i can go-- the other info you asked for I do not have- I used propane as my backup since that was what my old furnace was already using- also my H2O heater uses it-- I believe the dealer referred to my HP as a 2 ton unit..

35 deg is too high and defeats the purpose not only for a nice hybrid system but also the Greenspeed. At least lower to 30 degree and make necessary adjustments from that setting when the real winter finally arrives.

IMO

It is my understanding based on what I have read, the Infinity Controller can be programmed to have a furnace and heat pump lock out temperature. For example the heat pump lock out could be set to 30 degrees, and the furnance lock out could be set to 35 degrees. When the temperature is in the 30-35 degree range the heat pump would first come on (low stage, then high stage). If the temperature can be be achieved in a specified time, then the heat pump would shut down and the furnace would take over. The spread between the two lock out temperatures can be set from 5 to 55 degrees. The factory default is none.

We're in Montreal; the balance point for a 3-ton Infinity Greenspeed is about 5 degrees F.
Why would you want to cut it off at 35 degrees - especially at 5.9cents/kW? The gas furnace is only for extreme cold weather and the defrost mode. Let it run!

Even in Canada's Region 5, a 2-ton Greenspeed has an HSPF of 11.3. In Region IV it has an HSPF of 13. Why else would you have bought a premium HP if not to run it in VERY cold weather?

SR

I agree, whole purpose of that heatpump is because it can keep up in extra cold temperatures when a normal heatpump would need auxilary. The user that would typically get a heatpump like that is someone without having gas.

Keep in mind OP has LP gas backup, not nat gas.

IMO

At 5.9-cents per kW I would have opted for an all-electric system. The only reason to have a gas system, LP no less, is if you live in an area with frequent power failures and want to back a gas furnace up with a generator. That said, because LP is so expensive is all the more reason to run the HP.

Infinity GreenSpeed should have a COP of 3.31 with a HSPF of 11.3 and a COP of 3.8 with a HSPF of 13, depending on the region. That should still be better (cheaper) than a 96% efficiency gas furnace - unless the price of propane is REALLY cheap!

SR

At 5.9 cents, that is cheaper than NG 99% of the time.

I just had a 4 ton unit installed, all electric system. I live in Southwest VA. I have currently set my Electric Lock out at 25 deg, looking to lower that even more as the temperatures drop. Wasn't exactly sure where to set the initial setting but knew it should be lower than most conventional heatpumps. Would love to be able to drop this down to below 20 deg if possible and still get the heating performance from the heat pump.

Re: Jess4

Your 4-ton infinity Greenspeed should put out about 28Mbtu at -7.6 degrees Fahrenheit, at 0 degrees Fahrenheit it puts out about 34MBtu. Let it run ALL winter! That is what we do here in Montreal.

SR

the lockout temps above would be correct for a conventional infinity heat pump with 2 stage compressor. the new greenspeed with variable speed compressor has solid performance ratings down to 0-10 degrees f. I am a carrier dealer. I would consult with your carrier dealer to get the proper settings for optimal efficiency.