Gas Pilot Lights

Some thoughts on gas pilot lights.

Pilot lights are used on some natural gas or propane appliances (water heaters, dryers, fireplaces, stoves, ...) to light the main flame. These pilot lights stay on 24/7 to light the main flame when required. While most modern gas appliances use some form of electronic ignition instead of a pilot light, there are still many appliances out there with pilot lights.

Various sources report that a pilot light burns from 5 to 12 therms of a gas per month depending on the particular appliance and how the pilot is adjusted. At $1.50 a therm for natural gas, this would be $7.50 to $18 per month per pilot light. For $2 per gallon propane, it would be about $11 to $26 per month!

So, there is a definite cost associated with a constantly burning pilot light.

A constantly burning pilot light also adds heat to the house. Using the numbers above, a pilot would add about 17,000 to 40,000 BTU per day to the house. This heat can be useful in the winter when it helps to heat the house, but, in the summer it just adds to the unwanted heat load, and makes the house hotter or requires more AC on time. Even in the winter, the appliance may be located in an area of the house (e.g. a utility room) that you really don't care about heating, so the pilot light energy is largely wasted.

Some strategies:

If you are buying a new gas appliance make sure it has electronic ignition, and does not require a standing pilot light.
For appliances like furnaces or fireplaces, turn off the pilot except when its needed in the heating season. This will save money on the gas bill, and keep the house cooler. It may also save money on the AC bill. It will also reduce greenhouse gas emissions.

Some people may pay a minimum gas bill that covers the cost of a pilot light in the summer, so they feel there is no benefit to turning it off. This is bad bad logic. The pilot adds heat to the house all summer when you don't want heat, and running a pilot light for 6 months unnecessarily will generate about 450 lbs of CO2.

See: http://www.infinitepower.org/calc_carbon.htm

A Pilot Light Water Heating Strategy

This is kind of amazing.

Don, who runs the 12man.com website, has his gas water heater set up so that the main burner cannot come on. In his case, the pilot light alone heats all of the water needed by 2 people. He goes a step further, and does not vent the hot water tank to the outside, and actually restricts the water heater flue passage so that less heat is lost by convection through the flue opening. The justification for doing this is that the pilot light alone is no larger than the pilot light on a stove or gas refrigerator, and these are safely run without and outside vent. While I don't see anything wrong with this logic, I'm not sure I would go this far, as it seems to be getting a bit close to the boundaries of safety. But, it is amazing to me that a standing pilot light can supply this much hot water -- it gives some feel for how much energy a pilot light wastes.

Here is a link Don's description of the system, and how it has worked out:

http://12vman.com/e107_plugins/content/content.php?content.7

Any thoughts on this? email me Gary

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 **

Here is an article from Pandscorp that provides more detail on the ins and outs of heating water with a pilot light only...

More Pilot Light Information

Nice calculator for Natural Gas appliance energy use and cost, including pilot lights:

http://www.wisconsinpublicservice.com/home/appcalc_gas.asp

Pilot Light Energy Use:

http://www.clarkpublicutilities.com/Residential/TheEnergyAdviser/06_03_26

"Pilot lights waste over 20 percent of the gas in the US" Dec, 2005

http://www.utilities.cornell.edu/utl_labtips.html

Gas Fireplace Pilots Study:

http://www.homefamily.net/index.php?/categories/consumersmarts/turn_off_pilot_lights_and_save/

** The Calculation: If the water needs to be heated from 50F to 110F, then 20,000 BTU would heat:

Water per day = (20000 BTU)(1/(110F-50F) (1 /1 BTU/lb-F) (1 gal/8.3lb) = 40 gals per day at 100% efic

If the efficiency were 75%, it would heat about 30 gallons per day.

Gary 5/28/07, May 4, 2008