Incandescent bulbs and heating

One of the popular complaints about the push to ban incandescent light bulbs is that a lot of people have been relying on them for heating.  Pretending that all the heat emitted is captured for heating (probably not a good assumption--entropy can never be zero), let's do an analysis.  (Wikipedia  does a simpler version of this)

Here are the cases:

* If you're cooling the building, the more heat the bulb emits, the worse.  Period.  Better to keep the heat out of the building.  Switch to lower heat bulbs, like LED or CFC.

* If you're heating the building with energy that costs the same as electricity, i.e. a resistance heater (e.g. electric baseboard or space heater), the thermal efficiency of incandescent lightbulbs and the resistance heater are very similar and the energy use/cost are thus identical.  Light bulbs, however, burn out fairly quickly while electric heaters last a long time.

(One factor that may be important:  The room may not have a separate heater, and the light bulbs were emitting enough heat to keep it comfortable.  Switching to low-heat bulbs may undermine this, and replacing them with an appropriate heater may be more trouble than the energy saving)

* If you're heating the building with something that costs more than electricity (e.g. gasoline), the light bulb is cheaper.  You should probably think about getting a resistance heater.  (this may not be practical in all cases, e.g. on a boat at sea)

* If you're heating the building with something that costs less than electricity (basically everything except gasoline...or burning money...), then you can lower your heating bill (and environmental impact) by switching to lower heat bulbs.   Here's a nice calculator that enumerates quite a few of the cases.  In case it goes away, here are the numbers at at the time of this writing:

Energy Source	Cost/MBTU
Electricity@ $0.09/kwhr	$26.37
Electricity@$0.12/kwhr	$35.16
Electricity@$0.046/kwhr	$13.48
Natural Gas	$17.38
#2 Fuel Oil	$33.25
Gasoline@$3.75	$41.25
Hardwood	$16.66

The prices of these commodities varies a lot.  12 cents is the national average for electricity.  Puget Power charges 9 cents here in suburban Seattle.  Seattle City Light charges 4.59 cents.  (30 years ago, PP charged 3/4 cent, about what SCL charged then.  Thanks, WPPS.)

Heater efficiency is complicated.  These days, natural gas furnaces over 90% are common.  Electric heaters and light bulbs are a little higher, but not much.   Since these are the major cases we're comparing with light bulbs, we can ignore the inefficiency differences for the most part although  the calculator (and the numbers above) factor these numbers in.

Heat pumps are an interesting special case.  Because their calculated efficiency is usually higher than 100% (COP>1...it's sounds like a second law of thermodynamics violation but it's not: they're stealing the heat from elsewhere) it's a significantly better use of electricity than a light bulb or resistance heater.

Bottom line: there's really only one case where it makes sense to stick with incandescent bulbs:  where other types of heater are impractical for some reason, and incandescent bulbs provide sufficient heat to keep the room comfortable.  In all other cases, lower heat bulbs use less energy

(There may be other reasons to stick with incandescents--for example, the aesthetics may be preferred, but that's not my topic for today)