Our Trane 5-ton unit is a bit older: XL19i 19 SEER / 8.2 HSPF. It is rated to stay off of the resistive backup furnace down to the low teens. I would expect a newer unit with an HSPF of 10 to get you down to about 10F.iPlug wrote:We're debating whether we would need a back-up natural gas furnace (dual fuel) if we change our AC to a heat pump. Do you find that your heat pump can keep up with your low temps or do you go to resistance or natural gas heating at that point?
It only gets as cold as the mid 20s for a few hours, <5 times a year here, so don't know if a backup natural gas furnace is worth the investment. Not sure the HVAC guys would even agree to tie in our old natural gas furnace if upgrading the AC to a new high efficiency heat pump system.
A Trane 5 ton XV20i 20 SEER / 10 HSPF unit looks pretty sweet.
The real trick with a heat pump is the ramp rate. We drop our temperature by 6F at 7:00 PM each night in the wintertime and ramp it up slowly in the morning. The issue is that on cold and/or windy mornings, the ramp may be too fast for it to make the setpoints in time, which kicks on the resistive heaters. As such, I just turn off the breakers to the electric backup furnace this time of year when I don't expect the temperatures to get below about 20F.
In your case, I certainly wouldn't install a gas furnace, but if you have enough electricity at your panel, you might want to add in a resistive furnace. That way you can have heat if/when the outdoor unit has issues.