Hi Dan,

A standard billing measure for natural gas sold in the U.S. is a
"therm". One therm contains 100,000 BTUs. Alternatively, it is
sometimes sold in 100 cubic foot increments (CCF). Assuming a gas
furnace with an AFUE rating of 92 per cent, your net heat gain in
either case is about 27 kWh.

Natural gas prices can fluctuate widely from one year to the next, but
according the DOE, the average retail price for natural gas sold in
Washington state in 2006 was $1.34 per CCF. Again, assuming an AFUE
of 92 per cent, that puts the equivalent cost per kWh in the range of
$0.05. As of September 2007 (the latest month for which data is
available), it is $1.63 per CCF or $0.06 per kWh(e).

The current minimum HSPF or "heating season performance factor" for
air-source heat pumps is 7.7; like AFUE ratings, higher numbers are
better. A good quality heat pump with a HSPF of 8.5 will provide, on
average, 2.5 kWh of heat for every kWh of electricity consumed. If
you currently pay $0.08 per kWh, your effective cost per kWh of heat
falls closer to $0.03. On that basis, the operating costs of a high
efficiency natural gas furnace are 1.5 to 2.0 times higher than that
of our reference heat pump.

If my memory is correct, domestic natural gas production peaked in
1973 and the U.S. has been relying on natural gas imports from Canada
and Mexico to make up for the slack (and to a growing extent, LNG
imports from overseas). Canada's natural gas production has also
peaked and so I expect natural gas prices to trend upward going
forward (a succession of relatively mild winters and the loss of major
industrial consumers has helped to temporarily dampened prices, but
this won't last forever). Over the long haul, a heat pump would
likely outperform natural gas by a wide margin.

Hope this information is helpful.

Cheers,
Paul


"Dan" wrote in message
...
Recently bought a house in the Seattle area, built about 1980. At the
time the house was built, there was no gas in the area. The house has a
heat pump, which is nearing the end of its life. Natural gas is now
available in the area. I'm wondering if I should go with another heat
pump, or natural gas. Since about 80% of the electricity here is hydro,
it's relatively cheap, about $.08/KWH. I don't know what the price of the
gas is per cu', but I could find out. Is there a way I could get a rough
estimate of how much natural gas I would consume to heat the house, based
on the electricity used for this purpose? There are a lot of confounding
factors, the relative efficiency of the 2 units (old heat pump vs new
nat'l gas furnace), the fact that I also use electric to heat water, etc.
(can probably find some rough figure for factoring this out) the relative
costs of each type of replacement (I would add AC to the gas furnace, so
I'm guessing the gas/AC unit would cost more to buy initially than the
heat pump, especially if I have to shell out for the gas line to be run).
Coming from the midwest, electric heat was always seen as significatly
more costly than natural gas, but I don't know if this is still the case
just in general, and particularly if it would be true given this region's
relatively low electric rates. Any helpful comments appreciated.

TIA,

Dan