standby losses from the hotwater tank add up

strider3700 · 10-24-12, 07:08 PM

I decided to do some manual testing to see how a timer would do for me.
Last night I turned off the breaker to the hotwater tank. 18 hours later I turned it back on. There was no showers, baths, dishwashing during that time. Any hot water usage would have been hand washing and there was not a lot of that. Basically very little hot water usage in that time. The time for the tank to come back up to temperature was 10 minutes.

Now had I just left the breaker on it would have ran for 4 minutes every 3.5 -4.5 hours lets say 4. so in 18 hours it would have ran for 18 minutes. So it was a roughly 45% savings in standby time.

The tank uses 4.5 kw when running so those 8 minutes saved works out to .6 of a kwh. which is worth about 4 to 5 cents depending on my usage tier. So I'd save 219 kwh worth about 18 bucks a year. Most timers I see online are in the $50-$70 range giving a 3 or 4 year payback which isn't great in my mind. My electric company is giving me $75 if I reduce usage by 10% from last year which works out to 967 kwh so that radically changes the ROI.

Of course simply super insulating to reduce standby losses is likely to get me close to the same results usage wise. 2% of my total electric usage going to hotwater standby losses seems a little insane.

For now I'm thinking I can manually turn off the breaker after the last shower and then back on just before they start again the next day.

10-24-12, 07:08 PM	#23
strider3700 Master EcoRenovator Join Date: Dec 2008 Location: Vancouver Island BC Posts: 745 Thanks: 23 Thanked 37 Times in 30 Posts	I decided to do some manual testing to see how a timer would do for me. Last night I turned off the breaker to the hotwater tank. 18 hours later I turned it back on. There was no showers, baths, dishwashing during that time. Any hot water usage would have been hand washing and there was not a lot of that. Basically very little hot water usage in that time. The time for the tank to come back up to temperature was 10 minutes. Now had I just left the breaker on it would have ran for 4 minutes every 3.5 -4.5 hours lets say 4. so in 18 hours it would have ran for 18 minutes. So it was a roughly 45% savings in standby time. The tank uses 4.5 kw when running so those 8 minutes saved works out to .6 of a kwh. which is worth about 4 to 5 cents depending on my usage tier. So I'd save 219 kwh worth about 18 bucks a year. Most timers I see online are in the $50-$70 range giving a 3 or 4 year payback which isn't great in my mind. My electric company is giving me $75 if I reduce usage by 10% from last year which works out to 967 kwh so that radically changes the ROI. Of course simply super insulating to reduce standby losses is likely to get me close to the same results usage wise. 2% of my total electric usage going to hotwater standby losses seems a little insane. For now I'm thinking I can manually turn off the breaker after the last shower and then back on just before they start again the next day.