Nic

I suggest you read the thread by markt-it is on this forum's front page and he also lives in NC.

Trane has one HP model that has excellent performance/efficiency numbers-XL15i HP.

And of course you want to take advantage of NC's reasonable electric rates by leveraging with a HP for winter heating. Personally, I think dual fuel is overkill for your area/climate but this is my recommendation.

for downstairs, XL15i HP paired with the XV80 var speed gas furnace. Why? You will rarely need the furnace.

for upstairs, XL15i HP with matching var speed air handler-no furnace.

and pls do not use Trane stats. go with Honeywell VisionPro IAQ model for superior dehumidification control.

I also suggest a quote from Carrier or Bryant HVAC and from Trane's sister company Am Standard.

Carrier's Performance 15 HP, Bryant's Preferred 15 HP, and Am Std Heritage 15 HP are very good models.

Of course, you should request a load calc for accurate HVAC sizing as well as a thorough ductwork inspection.

IMO

thanks - one HP question - what happens when the temperature goes below 30 - does the HP cut off (not work at all) or does it go on but no heat comes out or does it go on but stays on because it can't get the area up to the thermostat setting?

nick

HPs are normally sized for cooling and any extra BTUs necessary for heating come from auxilliary/supplemental heat strips. Temperature balance point is the outside temperature where heat loss and heat gain is equal based on your home's inside temp comfort level. This temperature balance point varies from home to home primarily due to the tightness and insulation qualities of your home. Every home is different.

In a dual fuel system, an outside sensor is used to determine the point at which HP and gas furnace operation switches back and forth. I have my dual fuel set at about 30 degrees although it could go lower.

In a HP system with air handler, the backup heat strips kick in along with the HP operating when the HP can not keep up by itself. Keep in mind that as outside temperature decreases, a HP's performance and efficiency decreases but it still produces some heat. That's the reason for the auxilliary heat strips.

HPs have made very good improvements in the last five years and of course are very popular in area with reasonable electric rates and relatively mild winter climate like the South.

IMO