Heat
Ever wonder why you should turn the lights off in winter? I mean, it’s cold outside, and light bulbs are warm, so why not use them to heat rooms of a house?
Normal incandescent light bulbs are not very efficient, so they serve as better heaters than light sources. In the winter, I pay for natural gas to heat my home. I wondered if I could justify leaving lights on (out of laziness) by saving money on my heating bill.
First, the assumptions:
- The light bulb in my living room is 95% efficient at heating the space
- My furnace is 90% efficient at heating my living room
- Gas costs me $0.76 per therm
- Electricity costs me $0.09 per kilowatt-hour
What’s the cost of one BTU of heat from my natural gas furnace?
What’s the cost of one BTU of heat from my light bulb?
Well, that’s not good. It looks like it would cost me over three times as much to heat my house using incandescent bulbs as it would to use my furnace. I guess I’ll be shutting those unneeded lights off!
Of course, I’m not really concerned about power consumption — my home computer is on 24/7, and it draws the same power as many light bulbs. Brings back memories of heating my dorm room using my computer in college…
where’s the 2.93E-4 from?
my room is kept mostly at a reasonable temperature due to my computer…the house stays at ~60, my room in the upper 60s….
disregard. i am retarded. Energy / Energy = ~1.
Since it looks like these are just conversions I’m assuming you’re only taking into account the heat from convection and totally disregarding the radiation component which would be prevalant in the lightbulb.
I’m assuming that 95% of the heat from the bulb goes into heating the room. The heat could be transferred by radiation, convection, or conduction. As a corollary, I’m assuming that 5% of the energy going into the bulb is lost, prinicibly by radiation of energy out of windows.