Saving electricity

[BobRip]

It will save you money, but not a lot and it adds inconvenience. Ronmar's analysis was pretty good. However if you can time it so that the power is turned off before it fully reheats from your showers then you will save a little more since the average water temperature in the tank is lower and loss will be lower.
Definitely insulate the pipes, both the hot and cold. Touch the cold pipe when you have not run any hot water for a while and you will see that it is hot. You are paying for this loss. Also insulate the tank. I have a Marathon hot water heater and it has foam insulation. Also a life time tank warranty. It will hold the heat much better.

Losses to a heating space do add heat, but if you have a heat pump then it will heat 2 to 4 times more efficiently. Also the heat loss in the summer will add to your air conditioning bill.

I have used a timer for 20 years and finally disabled it because of the inconvenience and the Marathon water heater.

 

[ctpres]

Ronmar proves that this is the place of higher lerning. Wow I love this place.

--------------------------------------------------------------------------------Thatguy

"Kill-a-watts work on 100 volt appliances only."

True. But 220 is really 2 110's. If you wanted to you could use two Kill-o-watts. One on each 110 leg. Also using just one on one half of the 220 would give you a reasonabbly good answer. BUT Kill-o-watts will have a maximum wattage rating and I would guess that to be 1500 watts so you could only use it (one or two) if heater is rated at 3000 watts or less.

 

[Egon]

There are "On Demand " units that will mostly eliminate the "Heat Lost" during no usage times.

 

[RonMar]

Bob touched on a good point. I didn't account for any plumbing losses in my example. It assumed that all the pipes connected to the hot water heater were insulated to the same standard as the tank. Any plumbing losses would greatly accelerate the heat loss from the tank.

The pipes do not have a lot of surface area compared to the tank, but they are probably copper, which is way more thermally conductive than the steel tank. A bare pipe connected to the top of a water tank will act like a heat pipe and and will have internal convection currents. The water cooled against the skin of the pipe being more dense will fall back into the tank. Warmer water from the tank will replace this falling cool water up thru the center of the pipe. This is a form of thermal siphon. It is also the same principal the engineers used to keep the perma-frost frozen under the heated alaskan pipeline without requiring any power...

Insulation is your friend when storing heat in water. That heat loss figure for 120F water in a tank with 1" insulation of 25 BTU/SQFT/HR drops to 12BTU/SQFT/HR with 2" of insulation. It drops to 9 BTU/SQFT/HR with 3" of insulation... Insulate, insulate, insulate. It is the biggest bang for the buck IMO.

 

[BobRip]

The water cooled against the skin of the pipe being more dense will fall back into the tank. Warmer water from the tank will replace this falling cool water up thru the center of the pipe. This is a form of thermal siphon. It is also the same principal the engineers used to keep the perma-frost frozen under the heated alaskan pipeline without requiring any power...

.

I understand that some tanks have a check valve to stop the thermal siphon. I have no idea how well this works. Insulation as usual will help.

 

[BobRip]

There are "On Demand " units that will mostly eliminate the "Heat Lost" during no usage times.

I think the on demand is OK if you have gas. The electric takes a lot of electrical service to operate and will probably not allow several faucets to be used at one time. It would also require a big generator if you are running on one of these. Does anyone have one of the electric on demand units? How well does it work and what are the restrictions? My knowledge on these is only theoretical.

 

[RonMar]

I understand that some tanks have a check valve to stop the thermal siphon. I have no idea how well this works. Insulation as usual will help.

A check valve on the tank outlet would stop the type of siphon loss I described, but you would need one on both the hot and cold water lines if both run upward from the tank. Heavy insulation will also stop the process, as the thermal siphon process is powered by heat loss/transfer.

You can also sometimes get siphon losses if the hot and cold are connected somewhere in the home(malfunctioning mixing faucet valve?). I recall reading about a product called a thermal lobster or hot water lobster. It is I believe a thermally actuated valve, that allows the siphon process to bring hot water to a sink and maintain the water temp at that sink so you have instant hot water. It basically connects the hot and cold lines together and allows the water to flow up the hot line to the valve. When it senses warm water, it closes and stops the process. As it cools it opens and again allows flow. Since plumbing is typically not as well insulated as the tank, it looses a lot of heat, so this type of constant availability instant hot water, although convenient, is very wastefull of heat(saves water though).

 

[buckeyefarmer]

Kill-a-watts work on 100 volt appliances only. Maybe spend a month manually flipping the breaker off at night and check your bill.

My house has a 240V KWH meter, and I suspect yours does also.

 

[buckeyefarmer]

Ronmar proves that this is the place of higher lerning. Wow I love this place.

--------------------------------------------------------------------------------Thatguy

"Kill-a-watts work on 100 volt appliances only."

True. But 220 is really 2 110's. If you wanted to you could use two Kill-o-watts. One on each 110 leg. Also using just one on one half of the 220 would give you a reasonabbly good answer. BUT Kill-o-watts will have a maximum wattage rating and I would guess that to be 1500 watts so you could only use it (one or two) if heater is rated at 3000 watts or less.

Most Hot water heaters are 240V, 1ph, 2 wire. There is no neutral, so you would have to use a 240V, 1ph meter.

 

[irvingj]

I cheat.

I've got a water-source ("geothermal" these days, I guess...) heat pump that uses a desuperheater to shuttle heat to the DHW whenenver it runs.

During the winter, when heat pump's running a lot, it will consistently keep the DHW tank at around 90 degrees. I also have off-peak billing.... so I turn on the water heater disconnect in the early AM, shut it off when I leave the house for work. Best of both worlds, I'm thinking! DHW pressure tank is also covered with 1" Armaflex, 80-gallon electric water heater purchased with heavy insulation package.

Oh- and in the summer, I can flip a switch for A/C.... (shhhh...whispering here...and if it's laundry day the system will take house heat and put it directly into DHW.) Never regretted the additional installation expense 23 years ago!