[nostromo]

I get an early start on my veggi garden with a few grow lamps in my basement each spring.

The energy is "free" because the furnace would run more without them anyway.

By the way, if you live in a cold environment and wondered why using LED bulbs didn't make any dent in your electricity bill, it's because your furnace runs more now without hot bulbs.

[rconti]

If your house is well-enough insulated for that to be true, you wouldn't need much heat in the winter anyway!

For most of us, forced air is far more efficient than lightbulbs spewing heat up into the attic.

[tsomctl]

Only if you rely on resistive heating, which most people don't, because it is ridiculously expensive.

[xenadu02]

Indeed; if you must use electricity to get heat you should use a heat pump which is 2-3x as efficient as resistive heating. A resistive load is 100% efficient. A heat pump moves heat from outside to inside the home so for the same electricity you can get 200-300% efficiency. (Make sure you get a scroll compressor though; the heat they put out is quite a bit warmer than the older piston-style compressors).

If you're thinking this sounds a lot like an air conditioner you are correct: Most residential heat pumps are just A/C units that can be run in reverse during the winter. They work well so long as the ambient temperature is high enough to allow the liquid refrigerant to evaporate (some low-temperature models can effectively heat a home when the outdoor air is around -10 deg C / 20 deg F).