I have a Bryant 286ANA024-B ASHP. When it was installed our contractor set the switch-over from ASHP to the natural gas furnace at 25F and told me the unit was good to about 20F. I am now looking for actual spec's on what it should or could be run at. I looked all over the Bryant site and can't find it anywhere. I guess what I am really looking for is a chart with outside temp and COP so say at 40F it's 3.0 35F 2.8 30F 2.0 and so on. I am just wanting to double check the point at which I should be switching over.

There are several missing pieces of information, not the least of which is your local price structure & rates for gas & electricity, and the steady-state or AFUE efficiency of the gas furnace.

Then there's the not inconsequential inanswerables, since it's part of the actual system as-designed, ducted, and installed, which is the total power use of any air-handlers and the duty cycle need under different heat loads with the ASHP vs. the gas fired system, and the heat load of your house at 0F vs. 25F or any other temp. The full system power COP isn't reflected in the compressor's COP, and it will vary significantly with the actual design & implementation. With most mini-splits the compressor and blower power aren't separable, and the rated COP under various specified are pretty much the system COP (at mid-speed on those with variable speed compressors.)

If you're in buck-fifty a therm land, and can get off-peak power at 3cents/kwh even when the COP has fallen to 1.0 you basically NEVER switch over until the ASHP can't actually keep up. The 25F temp may have been based on that factor, since the rating on the 286ANA024-B is 19.4KBTU/hr (under some unspecified test condition see: http://www.furnacecompare.com/heat-pumps/bryant/286ANA024-B.html .) If, say your design condition heat load is 40bTU/hr @ -15F, your heat load at 25F is going to be about half that, which is the full-output rating of the Bryant.

That model uses Puron (R410A) refrigerant, and while may be a lower-bound operating condition for the compressor, but I'd be shocked if it was anywhere near as high as 20F. Some R410A mini-splits with scroll compressors can operate at -10F or even a bit lower with a COP >1, although most are already sub-2 at +5F.

Right I watch the natural gas / electricity rates monthly. This month we are at .8651 / therm (changes monthly) and .0699 for off peak and .2187 on peak. I do have a control box that takes the three thermostats in, and has an out to the furnace, out to the air source and is connected it to the utility break so it only uses ASHP off peak, if heating is called for off peak the natural gas furnace just kicks in. The controller also is where the 25F is set to switch over and also how long it lets a heating call run on the ASHP before it switches over, initially it was set to 60 minutes I switched it to 120 minutes. The furnace itself is a Bryant Plus 95s.

I understand the COP drops as it gets colder outside and would run longer and longer to keep up. I also understand the colder it is the more defrosting it will do also lowering the COP. What I am really curious about is what is the unit is actually rated to, bottom temp wise 20F, 15F, 10F or even lower? It seems odd to me no where does it say to not run the unit below xxF, it does say in cooling don't run it below some outside temperature and in heating mode it can't be above I believe 80F. Maybe if that is the case I shouldn't worry about it.

Our heating loads are low on this system because we supplement with the in floor from the geothermal unit which primarily heats our pool and desuperheater as well as the floors. I can get by without running any furnace calls to about 25F if all the floors are running. What I am trying this year is not running the in floor and only running the ASHP to see if the horizontal field is warmer next spring. Although I am guessing below 30F I am better off using the in floor via geothermal.

You won't be able to find how low your heat pump will go because it is based on your house's conditions. Your heat pump and pretty much any heat pump will run down to -20 degrees but it won't be able to heat your house. You need to find what your heat loss is at each outdoor temperature and then find what the output of the unit is at each temperature and find your balance point, the point at which the heat pump only puts off enough heat at a certain outdoor temperature to maintain the heat based on the heat being lost at the same temperature. Each company sizes differently and it depends on climate, electric/gas rates and your house's load conditions. In my area we typically size for 30-35 degrees before switching to gas, but if there is electric as a backup the heat pump will run as long and as cold as it is outside.

Hope this makes sense.

Yup totally makes sense. I was just worried about the physical unit itself. I remember in the 80's when my parents had a ASHP they couldn't run it below 25F or it could damage the unit somehow but apparently I don't have to worry about that with this new one.

I understand the diminishing return as it gets colder out but I think I will lower the change over outside temp from 25F to 20F, again after calling for heat for 120 minutes the control box will just flip over to gas anyway.

Thanks!