Water Heater Effiency

[G_and_D]

We use our hot water for dishes and showers in the morning and dishes at night. It seems like a waste of propane to leave the heater on when were not using hot water. I realize it takes time and propane to reheat the water but it seems that shutting the heater off and reheating each AM and PM would save propane.

Can any experts on heating mass and propane provide their expertise.

Thanks

[Almot]

LynnandCarol wrote:
It only takes about 30 minutes for ours to heat (or reheat).

It takes 5-6 minutes to heat amount of water needed for dishes in a pan on a stove top :)... This would be ultimate solution for energy conscious people. Shower is still a problem though.

[SaltiDawg]

thanks, pianotuna. I see the math now.

[pianotuna]

Hi Salti,

No I used 80% for the conversion from electric (which is 100% efficient) to propane. That is a guess.

So the 1.8 kwh per day is pretty much accurate.

SaltiDawg wrote:

pianotuna wrote:


My back yard testing was done at about 22 C and encompassed 24 hours of non use. It is pretty much "in the ball park". The extrapolation to propane use may be suspect.

And again, "You used 80% efficiency for the resistive heater?"

[SaltiDawg]

pianotuna wrote:


My back yard testing was done at about 22 C and encompassed 24 hours of non use. It is pretty much "in the ball park". The extrapolation to propane use may be suspect.

And again, "You used 80% efficiency for the resistive heater?"

[Old-Biscuit]

I like hot water when I want it, so WH is turned ON when we connect water and turned off when we get ready to leave.

If I have to save pennies in order to use my RV...well then it's time to stop using it.
I don't turn my water heater ON/OFF at home either.

BUT that is why things have on/off switches......owner can choose when to use.

[pianotuna]

Hi doug,

My back yard testing was done at about 22 C and encompassed 24 hours of non use. It is pretty much "in the ball park". The extrapolation to propane use may be suspect.

doughere wrote:
You WILL save by turning the heater off. pianotuna estimate of waste is probably a little too high, you could use that as your benchmark worst case. Is it worth your effort or not, or do you have need for water at high temp more often than not. I changed the fixed 140 degF thermostat to an adjustable set to 120; this saves a little and prevents scalding. We keep heater off when not needed; saves a little more.

Doug

[SaltiDawg]

Bobbo nailed it! Great response.

[doughere]

You WILL save by turning the heater off. pianotuna estimate of waste is probably a little too high, you could use that as your benchmark worst case. Is it worth your effort or not, or do you have need for water at high temp more often than not. I changed the fixed 140 degF thermostat to an adjustable set to 120; this saves a little and prevents scalding. We keep heater off when not needed; saves a little more.

Doug

[Robert78121]

As a full-timer I can assure you that turning it off will save propane. The key is to plan your hot water usage ahead of time. In the Summer, I would only run my hot water heater for around 15 minutes before taking a shower. That's is for the day unless I needed to wash dishes that day. How can leaving it on all day be more efficient than that?

Also, if you haven't considered it, think about converting your HWH to a hybrid with one of the commonly available electric conversions. That's what I finally did, and now I have hot water heater 24/7 and it's on the park's dime.

[Bobbo]

I am going to post 2 extremes as examples.

If you are using hot water continuously, you need to leave the propane on.

If you only use hot water once a week, it is far better to turn off the propane till you need it.

Somewhere between those 2 extremes is the point where the 2 lines intersect re: efficiency vs economy. Where is that line for you? Only you can really decide.

[SaltiDawg]

pianotuna,

You used 80% efficiency for the resistive heater?

[I_am_still_wayn]

G and D wrote:
We use our hot water for dishes and showers in the morning and dishes at night. It seems like a waste of propane to leave the heater on when were not using hot water. I realize it takes time and propane to reheat the water but it seems that shutting the heater off and reheating each AM and PM would save propane.

Can any experts on heating mass and propane provide their expertise.

Thanks

Do you turn your water heater off and on in your stick and bricks house? IF no, why not if you think it is worthwhile in your RV? If yes, then why are you just considering doing that in your RV?

The reality is that there are tremendous variables that preclude any one answer to include the ambient temperature, the temperature of the incoming water, as well as the amount of use of the hot water. I have done both and discovered that while I might save a very small amount of energy, I lost much in convenience, especially when I forgot to turn it on in the morning and wanted to take a quick shower.

[pianotuna]

Hi,

I did a test. If no water is drawn the water heater will cycle every four hours and on electric will draw power for 15 minutes. That's six (needless) cycles per 24 hours. The electric heater draws 1200 watts so that is 1.8 kwh or about 6200 btu's. Assuming 80% efficiency for the burner bumps that up to about 7800 btus.

There are about 21,000 btus in a pound of propane. so it will burn 1/3 pound per day x 30 days = 10 pounds per month (for doing NOTHING).

I cycle mine in the morning. There is enough hot water left over for hand washing and dish washing until the next morning.

[korbe]

We turn our WH on when we start the coffee in the morning, and again when we sit down to dinner at night. The WH gets a hard turn off when the water is hot. I see no reason to keep the water hot when we don't need it. We are weekend campers and the process may change if we lived in our unit full time.

And yes it takes more energy to maintain hot water than to heat it each time.

[LynnandCarol]

It only takes about 30 minutes for ours to heat (or reheat). We turn on before we plan the showers/dishes and then back off till needed again. After it is turned off the heated water stays warm in the tank for a long time for hand washing. Saving is saving whether small or not.