economics of heat

let's discuss the cost of home heating briefly. in a recent discussion, someone told me it would be cheaper to use a gas furnace to heat the house than a heat pump. a quick google gave me a page comparing the options like so:

propane (95,000 BTU/gal) @ $2.83/gal = $29.79/million btu
oil (140,000 BTU/gal) @ $3.11/gal = $22.21/million btu
elect (3410 BTU/kwhr) @ $0.14/kwhr = $41.06/million btu
nat gas @ $15.15/million btu

the author also made note that nat.gas is more locally produced energy, most propane comes from processing nat.gas (which makes it more expensive), and oil pricing is volatile.

i adjusted the prices to the DOE outlooks for 2011. from this comparison, nat gas appears to be the least expensive. however, the efficiency rating of the furnace will reduce the number of BTUs used to heat your home. the other BTUs go out the flue pipe...

except for heat pumps, which don't have flue pipes. in fact, the efficiency ratings of the heat pumps i'm looking at actually *increase* the number of BTUs used to heat the home. common rating indicators used are HSPF or heating COP.

COP is a direct ratio of energy consumed by heat pump to energy moved into the house by the heat pump. A COP of 3, for instance, means a heat pump would consume 2kW to meet a 6kW load. The COP of a heat pump varies depending on the conditions (indoor & outdoor coil temperatures.)

HSPF is a ratio of energy consumed to energy moved, but over an entire simulated heating season (including the various indoor/outdoor conditions.) HSPF varies with geographic location, but most equipment specifications are listed for 'region IV'..

You can convert HSPF to an average COP value like so:
avg COP = HSPF / 3.413

The Fujitsu i mentioned earlier had an HSPF of 8.6. avg COP = 8.6/3.413 = 2.52

now we can take that average COP and multiply it by the BTUs per kwh listed for electricity in the energy rates i listed at the beginning of this blog..

elect (3410 x 2.52 BTU/kwhr) @ $0.14/kwhr = $16.29/million btu

this is just slightly more expensive than natural gas, with $15.15/million assuming a 100% efficiency furnace. the best ones are rated 95+%.. at 95%, it's $15.95/million.

if you recall, there were other inverter systems i considered selecting. one i've had my eye on for a while is seemingly well oversized for my needs. it is a samsung unit, UH105CAV + DH105CAV. one zone, one interior unit with a 'medium static pressure' blower. with an HSPF of 9.3...

9.3/3.410 x 3410 BTU/kwhr @ $0.14/kwhr = $15.05/million

this unit will be cheaper than a 100% afue natural gas furnace to operate.
but wait, there's more..

one of the first units i was considering was a sanyo, the 26UHW72R, one zone with a single indoor blower that can handle medium static pressures also. this unit has an impressive 9.7 HSPF rating. *however, i just discovered the ahri listing for this combination is 9.0 HSPF... :\

9.7/3.410 x 3410 BTU/kwhr @ $0.14/kwhr = $14.43/million

sweet. however, the sanyo costs $400 more than the samsung. the samsung will be able to heat the house at lower outdoor conditions (perhaps 5F lower.) the sanyo is more closely sized to the house load, which means the predicted efficiency of the sanyo is likely closer to reality than the samsung. plus the sanyo would probably do a better job at reducing indoor humidity during the summer..

ah, decisions, decisions..