<VV> Heat Pumps

[Padgett]

>In regard to heat pumps,  those which are air-to-air (the usual) require a
>fairly warm winter  climate

Lowest I have seen in Orlando was 17F about a decade ago. More often we 
just hope for a few days below freezing to curb the bug population.

That said, we have a 50,000 btu heat pump for the house that is much more 
efficient than the 36,000 btu unit when we built the house cooling the new 
500 sq ft addition without any problem. The monthly bill in summer went 
down considerably when it was installed so they have gotten much more 
efficient..

Heat pumps themselves are good to about 20F and have electric coils 
(resistance heat) for lower temperatures. Before we had the new one 
installed, I had the electric strips disconnected for years and we never 
really noticed. We also have heaters in the ceiling fans in the bedrooms 
which I run on the low setting (800w) for really chilly nights.

The basic problem is that the heat cycle is basically an a/c in reverse and 
the outside air must warm the coils to function. Once the air temperature 
gets down to the working temperature of the heat pump, transfer stops. Most 
still use R-22 Freon which limits the working temperature just as high 
outside temperature limits the effectivity of the a/c. With the right 
medium you could get heat at far lower temperatures but it would cost a bit 
more.

So for temperatures down to about 20F, a heat pump can be effective and the 
EER is a whole lot beter than resistance heat but once it gets colder they 
do not work so well and "help" may be needed.

Padgett