Looking for Data on Lennox Heat Pumps

contrawise

Hi, Heating Helpers -
35 years in the industry, 6 years retired. It's good to be back!

Lennox has introduced a new line of air/air heat pumps this year. Checked their web site, but one piece of data that's important to me is not there. Which is - at what outdoor temperature do they recommend switching to back-up heat? Anyone have the scuttlebutt? I'm selecting a heat pump for my church's caretaker house. South Central Wisconsin.

Hot_water_fan

That’s never something that will be published, since it’s different for every application - it’ll depend on its capacity vs outdoor temperature, also fuel costs (since efficiency decreases as temps do). You might never need backup or you might need it at 30, you’ll have to do the work yourself. 

EdTheHeaterMan

That piece if information depends on the actual load on the equipment. For example:

If you needed 2.5 ton of air conditioning for a particular building and you decided to use a 3 ton thinking that the added capacity on the heating side will offer more lower cost heating down to say 21° before needed to add back up heating capacity.

If your neighbor with the same exact home opted for the 2.5 ton unit and therefore the break even point of that heat pump capacity was 29° before the back up heat was needed. What would you tell Lennox to publish as the break even point? 21° for the 3 ton and 29° for 2.5 ton units? What if you put the 3 ton unit in a home with an actual 3 ton cooling load? Would the 29° still work for that larger home? I think not.

Just as no two homes are each exactly alike even if the same builder used the same blueprint. You, a single person that lives alone, will not open and close your doors the same amount as your neighbor with 6 children, even if the home is identical in every other way.

I can guarantee you this: Every heat pump backup will kick in as soon as the heat pump reverse cycle is not enough to maintain the first stage temperature setting on the thermostat. As soon as that second stage calls for heat, the back up will be energized regardless of the outdoor temperature.

Heat pump thermostats have a way of doing that automatically

contrawise

Thanks for your reply. Yes, I'm familiar with the math. Problem is, local dealer has not returned promised phone calls. So, don't have the data to do that math. Every other contractor I have talked to has told me what they recommend.

Hot_water_fan

Thanks for your reply. Yes, I'm familiar with the math. Problem is, local dealer has not returned promised phone calls. So, don't have the data to do that math. Every other contractor I have talked to has told me what they recommend.

Sounds like they’re winging it. You can’t find them online? Mitsubishi and Trane post capacity vs temperature charts. Sorry the dealer is offering poor service.