Saving Money by Keeping Hot Water Heater on "Low"?

December 31, 2008 4:13 PM

Am I saving myself money by turning my propane heater to "Low" when I'm not using hot water?

I live alone, and usually only use hot water to shower, once a day. About 20 minutes before I take a shower, I turn it up only as hot as I need it, and turn it back to low before getting in the shower, as there is more than enough water for one shower, and I don't need it making me more hot water that's only going to get cold before tomorrow's shower.
I don't have laundry or a dishwasher, and after the shower there is usually enough hot (or at least warm) water left to do dishes if needed.

So am I really saving myself money by doing this? Or is it costing me money because once a day the water has to go from luke-warm to hot?

posted by Andrea2880 to Home & Garden (7 answers total)

In theory, you're saving a bit - the cooled-off water can't continuously lose heat all day. But the gas saved is vanishingly small.
posted by notsnot at 5:06 PM on December 31, 2008

Hard to say exactly without knowing how your gauge is calibrated. Does "high" burn twice as much gas as "low" or only 15% more? But yes, this will save you money on you gas bill, and potentially quite a bit. My water heater is on high from 9PM to 7AM daily, which leaves plenty of hot water for showers in the morning. This is a lot cheaper than running it all day, I assure you.
posted by valkyryn at 5:42 PM on December 31, 2008

You are saving some amount of money by letting it cool down until you need it again. How much, I don't know. Your could do an experiment. One day, before your shower, take a reading from your gas meter before you turn up the heater again, then take another reading just before your shower, but leave the water heater on. Then, the next day, take another reading just before your your shower. Now figure out the amount of gas it took to heat up the water the first time, and compare it to the amount of gas it took to replenish it after your shower, and then keep that water hot until your next shower. Find the difference, and you'll have an idea of how much gas you save. You should probably repeat a few times to average out fluctuations in air and water temperature, and the length of your shower.
posted by Good Brain at 5:44 PM on December 31, 2008

Ah, sorry, I missed that this was propane. I guess you'd have to weigh the tank using a reasonably accurate scale.
posted by Good Brain at 5:45 PM on December 31, 2008

Depends on how poorly insulated the water heater is.

If you were to do the calculations, don't forget to calculate in how many fewer times the water heater fires up during the time it's on low and subtract that from how much gas it takes to feed the shower.
posted by gjc at 7:00 PM on December 31, 2008

I wonder if there could be a health risk in you doing this. A friend's father contracted Legionnaire's Disease from underheated water. It almost killed him and he had lasting effects similar to those from a stroke. That was at a vacation cabin, however; your water doesn't go long at low heat, and that's good. On the other hand, based on your use of propane, I suspect that you may not be on city water, and that could mean your supply is prone to contamination of a number of different sorts, some of which may love lukewarm water, as does Legionnaire's (which is present at low level throughout many natural water sources). The typical advice is to make sure your minimum heat doesn't go below around 130 degrees.

To your question--I read something recently cautioning that, if you let the heat in your house get too low, you may waste more heat bringing it back up to temperature than in keeping the thermostat at a more temperate setting. Sadly I can't remember the source, but based on this (and on gut feeling, which is worth zero, I know) I believe you may be wasting energy rather than saving it.
posted by Herkimer at 7:58 PM on December 31, 2008 [2 favorites]

I opened this thread to say exactly what Herkimer said. Although rare, Legionnaire's disease is awful. The principle cause in the US is setting water heaters too low.
posted by JFitzpatrick at 12:12 AM on January 2, 2009