OT: tankless water heaters.

Anyhow, the new tankless unit suddenly started leaking last year. The company tried to tell her it had been mis-installed as the gas vent went thru the roof like the old one. They said it had to have a horizontal vent, no other way allowed. Problem was a pinhole in the outside radius of a tube in the heat exchanger, no relation to water condensation, corrosion, etc from the vent pipe. They finally relented and shipped her a new one and sent a authorized representative (plumber) to install it. He installed a new thru the wall stainless vent and this was a larger unit than the old one. She lives by herself and likes it. The more water you use, the higher the fire. You can turn on a faucet, and hear it start up, open the faucet more, hear it ramp up, go turn on the shower, it picks up even more.

Whole house electric units require huge feeds to run them.

Do some google searches for tankless water heater and see what you get, lots of info.

Charles

A 50 gallon tank of 125 degree water insulated to R11 which is kept in a relatively unheated space averaging 40 degrees (F) loses about $4.00 worth of energy per month to the surrounding environment. It is a basic heat flow problem and not difficult to calculate.

A gas water heater loses more than an electric water heater, since it has a center flue which can allow some heat to be lost to the center and then up the stack even with the burner not running. This can be combatted in high efficiency models, but I would still not expect the loss to be more than another $2.00 per month.

If the water heater is in a closet or your conditioned basement, then the standby heat loss is near zero in the winter time -- only that $2.00 per month going up the stack. The rest of the "waste" heat helps you heat your house and reduces the load on your furnace.

A tankless model with sufficient capacity for your household might cost $1200 and have a service life of 12 years. Your "savings" will be -$38.00 per year. (That is a net loss of $38.00 per year). And this does not consider the time value of money, which almost doubles the negative savings.

Tankless models make sense if you have space limitations, have a very intermittant demand, or need to winterize frequently. A shop sink comes to mind, as these can use smaller and less expensive models, little water is actually used, so the standby is a bigger relative factor, and you may not heat the shop in the coldest weather and have problems with freezing of an ordinary water heater.

But for a whole house situation, I certainly would not spend my tax return check on such a "savings".

I have actually measured my electric water heaters and found that it cost around $30.00 per month to operate them even when no water is being used. I attached a running time meter to them to find the number of hours of actual operation in a month. Multiplied by the amount of power drawn. At 8 cents per kilowatt hour it worked out to near $30.00 per month to operate each one.

Our water use is not high. Only 2 in family. When gone for a few weeks the cost to keep the water hot did not change by much, only a few dollars.
At the time I did the measurements I had a house with two 40 gallon water heaters. One in the garage and one inside the house in air conditioned space. House located in South Florida.

Regards
Gary

Call it 23 square feet.

If the water temperature is 125 degrees and the ambient is 40 degrees and the insulation is R11 then the heat loss is

23 * (125 - 40) / 11 or 178 BTU per hour

there are 24 * 30 hours in a month, so the heat loss is 178 * 24 * 30 = 128000 BTU per month

There are 3413 BTU per kilowatt hour, so we use 37.5 KWH to replace the lost heat. (Electric heaters are 100 percent efficient).

At 0.08 dollars per kilowatt hour, we have $3.00 per month. That's where I got the number I quoted.

Several of these assumptions may be optimistic. Assume the water heater is miserable cheap one insulated only to R4, and the water temperature is a toasty 140 degrees. Under these conditions we use 3 times as much energy to maintain the temperature, but that is still only $9.00 per month, or $18.00 per month per two water heaters.

(I have neglected conductive loss to the piping, but I don't think this amounts to much).

For a situation in Florida, the average ambient would be more like 60 degrees, which would make the heat loss more like $16.00 per month.

I cannot explain the $30.00 per month that you measured. Maybe you have a leaky faucet? Or maybe there was something wrong with how you did the measurement?

My own anecdotal experiences come from shops and houses sitting idle with the water heater left on. The only thing spinning the electric meter is the standby loss. At the end of the month it is easy enough to read the electric bill and observe the cost of the hot water sitting there unused. The figures I have seen are more consistent with the $3.00 to $8.00 range.

Will still take time to get hot water to the shower or wherever depending on the length of water line.

They do work well. They are expensive, they do last longer, they do gunk up over time depending on the minerals in your water.

Net analysis, good when you need spot hot water, but the tank heaters are cheaper and equally as reliable, maybe better than the tankless ones for whole house hot water.