Author Topic: Heat source: incandescent bulbs vs. blowing hot air  (Read 2012 times)

Radagast

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Heat source: incandescent bulbs vs. blowing hot air
« on: November 13, 2016, 07:55:07 PM »
I have somehow accumulated 6 old fashioned light bulbs in my house. I don't think I ever bought one directly, but I keep getting used light fixtures that they come in. So the question here is: are these old incandescent bulbs a more efficient way to heat a room than a natural gas furnace and blower? On the one hand natural gas is an efficient way to heat a house, but much of the benefit is lost when the warm air rises to the ceiling leaving occupants and especially their feet cold, plus it can leave through the cracks. On the other, electric resistance is not very efficient, but radiant heat hits all surfaces and humans and warms them evenly.

I am sitting in a room with a 260 watt incandescent space heater and I think it feels warmer with the light on. Further, the thermostat is also in this room and I have not done a scientific study but I think the furnace is running less. Am I misleading myself, or are incandescent bulbs an efficient way to heat occupied rooms?

Syonyk

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Re: Heat source: incandescent bulbs vs. blowing hot air
« Reply #1 on: November 13, 2016, 08:22:19 PM »
An incandescent bulb produces ~1kWh of heat (3400 BTU) for 1kWh of power - $0.08/kWh is a cheap power rate.

Call it 2.35 cents per 1000 BTU.

Natural gas is around $0.90/therm (100,000 BTU) - or at 80% efficiency, 1.12 cents per 1000 BTU.

That said, you're correct in that you have losses with blowing air, and radiant heat is a better way to heat humans.

Even with losses, natural gas should be cheaper - and I used a very cheap power rate in my calculations.

ShoulderThingThatGoesUp

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Re: Heat source: incandescent bulbs vs. blowing hot air
« Reply #2 on: November 14, 2016, 04:33:39 AM »
Purpose-designed electric space heaters and baseboard heaters are less efficient than natural gas heat. A light bulb near the ceiling will do a terrible job distributing its heat.

GetItRight

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Re: Heat source: incandescent bulbs vs. blowing hot air
« Reply #3 on: November 14, 2016, 06:34:48 PM »
Electric heat is always more efficient than any fossil fuel heat source, but it's usually more expensive. If you have incandescent bulbs use them in winter so they don't go to waste but swap for CFL or LED in warmer months to minimize heat and discomfort. The heat radiated will result in a minor reduction in the fuel your furnace burns, maybe measurable maybe not. I would not leave lights on in order to provide heat in lieu of the furnace running when I didn't wnat or need light, unless it was some emergency where the furnace was broke and I was waiting on parts and wanted every possible alternate heat source.

Radagast

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Re: Heat source: incandescent bulbs vs. blowing hot air
« Reply #4 on: November 14, 2016, 10:57:30 PM »
So lets see some math using Syonyk's input. I realized it is a 280w space heater light.
$0.127 I pay per kwhr electricity
213 watts used by current bulb in excess of LED bulb (280w -9.5w -9.5w -9.5w-18w , 3x60 watt bulbs + 1x100 watt bulb)
726 BTU generated per hour in excess of LED bulb
720 hours used in heating year (6 month x 30 day x 4 hour)
Cost to run light for remainder of heating year in excess of LED bulb = $21.40
Light generates 571,608 BTU's in excess of LED bulbs over course of heating year

That is 5.72 therms the furnace does not need to use. Assume the furnace is 80% efficient per Syonyk. I will additionally assume that the furnace as a heat source is only 60% as efficient as the light. The light is in the room we spend most of our time in, which also contains the thermostat and thus reduces heating. Plus the furnace has losses from stratification, escaping air, and it heats the entire house rather than the one room. The result is 11.9 therms, which means the furnace uses about twice as many therms as it needs to provide the same equivalent heat experience to us occupants. A Wild Ass Guess.
I pay $0.96/therm. $0.96/therm x 11.9 therms=
The furnace can provide the same heat as the incandescents for $11.44
The incandescents do it for $21.40 per above
The furnace and LED light bulbs will be $9.97 cheaper to run over the course of the next six months.
Even if I assume I will pay $30 dollars for LED bulbs and lose 3% interest on that over the course of six months, plus 3% depreciation of the $30 LED bulbs over six months, it looks like it will still be cheaper to switch to LED's.
The advantage to using LED lights and natural gas heat is $8.17 even after including 6% interest and depreciation.

Moral of the story: Natural gas and LED's seems to clearly beat incandescent bulbs by cost, per my calculations.

Darn, I was hoping it would tell me to take the easy way out :(

AlexK

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Re: Heat source: incandescent bulbs vs. blowing hot air
« Reply #5 on: November 15, 2016, 12:01:08 AM »
Incandescent bulbs are really bad in the summer because you are paying more for the light and more for the air conditioning as the extra heat needs to be removed. It feels wrong to throw something away when it's not broken but for the case of incandescent bulbs it's the right move.

Telecaster

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Re: Heat source: incandescent bulbs vs. blowing hot air
« Reply #6 on: November 15, 2016, 12:12:10 AM »
I have somehow accumulated 6 old fashioned light bulbs in my house. I don't think I ever bought one directly, but I keep getting used light fixtures that they come in. So the question here is: are these old incandescent bulbs a more efficient way to heat a room than a natural gas furnace and blower? On the one hand natural gas is an efficient way to heat a house, but much of the benefit is lost when the warm air rises to the ceiling leaving occupants and especially their feet cold, plus it can leave through the cracks. On the other, electric resistance is not very efficient, but radiant heat hits all surfaces and humans and warms them evenly.

Think about it this way:  The power company can take natural gas, burn it and turn it into electricity, and then you turn the electricity into heat.

Or you can turn natural gas into heat yourself.  Logically natural gas heat will be cheaper, and it is.

That said, you are onto something.  If you are only heating one room, or part of a room, that can be a lot more efficient that heating a whole house.  Just heating the spaces you occupy is a good way to go when you can.