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Old 11-08-10, 12:49 PM   #1
Daox
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Default Pilot light gas usage

I've been digging through sites lately for more ideas on conservation and I came across a builditsolar page on gas usage of pilot lights. I had no idea that my pilot light for my water heater could be burning 5-12 therms per month! My summer usage for gas (which would be all water heating except for some stove top use) is only around 14 therms. That means likely a huge bulk of that is the pilot light just burning away.

Apparently, a pilot light burning that much gas puts off a fair amount of heat too:

Quote:
How much water should you be able to heat with just a pilot light?

If you take 6 therms per month as the an average pilot light energy use:


Energy per day = (6 therms/mo)(100,000 BTU/therm)(1 mo/30 days) = 20,000 BTU/day


20,000 BTU per day is enough to heat about 30 gallons of water from 60F to 120F assuming 75% efficiency **

The page also has a couple links on it which tell of people using only pilot lights to heat their water, one of which goes back to a thread on ecomodder, our car oriented sister site.

Has anyone else tried or thought about this? I'd think you could make some sort of automatic flue damper and have the best of both worlds. If my summer usage is only 14 therms, theres a good chance I can get away with pilot light only heating, at least in summer.

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Last edited by Daox; 11-08-10 at 01:26 PM..
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Old 11-09-10, 12:21 PM   #2
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No thoughts on this eh?
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Old 11-09-10, 02:07 PM   #3
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Our furnace and on-demand water heaters don't have pilot lights which are on all the time. Instead, they have spark ignition. The furnace is plugged into the grid (pump+electronics), but the water heaters use two D size batteries, which get changed about once every 2 months.

Maybe it is possible to replace your pilot light with a spark ignition thingy? Or maybe the pilot light only heating would be easier.
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Old 11-09-10, 02:22 PM   #4
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Yeah, I guess there are benefits and drawbacks to both methods. With the pilot light only, you can't use a lot of water, but its very efficient. If you did the spark ignition, you wouldn't have the pilot light waste, but it would only heat while its on full blast and that wouldn't be as efficient.
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Old 11-09-10, 04:40 PM   #5
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My parents had natural for the furnace. They used to turn the pilot light off during the summer but found that they got a minimum charge for meter reading monthly that cost more then the pilot light used so they stopped. After moving they refused to buy anywhere that had natural gas in place and I specified the same with my realtor. Thats pretty much all I know about them
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Old 11-09-10, 04:50 PM   #6
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You can take a reading yourself: turn your furnace and HWH to "vacation" for a couple hours (or as long as you can stand) and take a reading. The smallest hand on my gas meter moves visibly with just a pilot light on (about as visibly as the minute hand on a large analog clock), but I didn't actually take a reading.

You'd have to defeat a few safety interlocks to modify the ignition system in a combustion appliance, and while the risk of disaster may be remote, I'd steer well clear of it.
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Old 11-10-10, 02:07 AM   #7
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Quote:
Originally Posted by Daox View Post
Yeah, I guess there are benefits and drawbacks to both methods. With the pilot light only, you can't use a lot of water, but its very efficient. If you did the spark ignition, you wouldn't have the pilot light waste, but it would only heat while its on full blast and that wouldn't be as efficient.
How about adding a heating element or pad to the hot water tank? It would turn on only when the pilot light wouldn't be enough.
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Old 11-10-10, 06:45 AM   #8
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Well, this post wasn't just about my water heater, it was about getting the word out about how much gas those pilot lights use.

My water heater is pretty old and I think when I replace it I'm going to go with a high efficiency natural gas boiler in its place since I plan to heat more of my house with hydronically heated floors in the future (just the sunroom is hydronically heated atm). This is one reason I can't just use the pilot light heating method. I do need the burner to kick in to keep up with the heating requirements.
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Old 11-17-10, 05:35 PM   #9
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I'll put in my 2 cents here.

From July until October I used 7 or 8 therms a month with a gas bill of about $15($8.50 is a 'basic service charge' that I pay even if I don't use any gas at all) which was no use of the furnace. I cook with a gas stove/oven and my electric dryer is electric(came with the house) even though I have a gas line right next to it.

So my water heating and cooking to put it simply is about 8 therms. What was interesting is I actually experienced what the pilot light can do when I left the house for a week on vacation and nobody else was home. I set the temperature down to vacation and when I came back a week later, the first thing I wanted to do when I got out of the car and into the house was take a shower so I went downstairs to the water heater and turned the temperature knob and once it got to the selected temperature I usually have it set to, I thought the water heater was broken because it didn't click to fire up the burner.

It turns out that just a little turn farther than where it was and the burner fired up at about 135 degrees and clicked off right at the 125 which is where I keep it at(halfway between 'A' and 'B'). So basically this means that the burner probably only fires up when I'm actually using the hot water and is maintained by the pilot.

I just went down and it wasn't running, I put my hand on the vent pipe and it was cold and I put my hand in the exhaust area under the hood and I didn't feel any heat. Putting my hand against the actual metal heat exchanger inside and that was lukewarm. I think the pilot might have a fairly efficient heat transfer and I wouldn't consider it all waste. ...but next time I go on a week vacation in the summer, I'll strongly consider cutting the pilot but that is likely going to save me $1.50 or less for a week.

For what it's worth, the energy star label says the unit uses 250 therms a year or $232 of gas. That math doesn't add up unless they figure a family of 5 people are using it. 250 therms/12 months=20.8 therms a month. I'm nowhere near that figure. It's a 9 year warranty unit installed in 2008, 40 gallons and a first hour rating of 71 gallons. According to the energy star label it is more towards the worst side than the better side of comparable units.
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Old 11-17-10, 05:41 PM   #10
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That's a good point: how can the pilot light "waste" energy, except that which escapes up the flue? And roughly the same percentage should be escaping up the flue whether the burner is running or it's just the pilot.

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