You might be pleasantly surprised. According to Nova Scotia Power's
web site, an air source heat pump "meets the full heating requirements
of your home at an outside temperature of -4°C [25 F] or warmer..." .

http://www.nspower.ca/YourHome/HomeE...ps/ashpqa.html

Obviously, that number is going to be determined by the capacity of
the unit; here in Nova Scotia, I assume heat pumps are likely to be
sized according to our heating rather than cooling requirements, so
your results may differ. In my case, my small (14,000 BTU) ductless
system will keep my home at a steady temperature down to about -2C
(28F). Below this point, the house will begin to cool gradually and
the oil boiler will kick on to make up for the loss.

Shifting gears for the moment... Regardless of the heating system you
use, your first priority should be to address any weakness in your
home's thermal envelope; proper insulation and good air sealing will
go a long way to reduce your heating and cooling costs and make your
home more comfortable. If your local utility or government agency
offers an energy audit service, this is a good place to start.

In the year prior to my purchase, the previous homeowners used 5,700
litres (1,500 U.S. gallons) of heating oil for heat and hot water --
and that happened to be a mild winter! Last year, without the benefit
of the heat pump, I was able to reduce this to 1,973 litres (525
gallons).

So far this year (August 15th through March 10th), my oil consumption
stands at 715 litres (190 gallons), much of this for domestic hot
water. During this same period, my heat pump has consumed just over
3,200 kWh of electricity and displaced approximately 840 litres of
heating oil. My net savings to date (after subtracting the cost of
electricity) works out to be $400.00 CDN ($350.00 US). By the end of
the heating season, I will have saved just over $500.00 on my total
energy bill.

So, from a strictly numbers point of view, even in our relatively
"cold" Canadian climate, air source heat pumps work amazingly well.
And from what I understand, properly sized and placed ducts, and
variable speed blowers help minimize some of the "cold blow" issues
that are often associated with this type of heat source.

Cheers,
Paul

On 10 Mar 2006 19:05:41 -0800, wrote:

I could be wrong as new tech changes things. But a few years ago the
rule was that unles you had a 50° air tenp the heat pump wasn't very
economical with an air to air system. In Mid Tennessee the in thing
is using the buried pipe as the heat exchange and is said is very good.