Water Heater Efficiency - combustion

[RichK]

Hi All,

All the talk about efficiency, lightbulbs heating the house, etc. Makes me think about water heater efficiency.

I assume, the published efficiency of a water heater is what it takes to keep the water at the set temp vs the entergy input. So anything getting out of the heater thorugh the insulattion is a loss.

This may be true in the summer, when you don't want to heat your basement. But in the winter, the losses into the basement are not real losses, as such.

I'm wondering: is the heater transfer from the gas burner to water more efficient, than by comparison heat transfer from furnace burner to the air (assume 80% furnace, no fancy controls).

Reason for this question is: Does it really make sense to insulate the water heater and hot water pipes, as some people do, in the winter ("blanket" type)?

My guess is that one can remove heat from the heater exchanger of the furnace faster, than transfer it to water

Rich

[Brian Attwood]

Probably depends. Would you heat your basement otherwise? If the heat leaking from the heater and pipes keeps the basement warmer than you need it to be then that heat would in effect be wasted. If you heat your basement anyway, then I guess it would depend on how efficient your water heater is compared to your furnace. Not insulating your pipes will waste water when you take a shower, etc, as you wait for the pipes to heat up, but for most that is probably not a lot in terms of money.

[m Ransley]

Most of the energy is waisted up the flue to the outside, the other losses are standby, heating un needed water, lime scale and inefficient

80% burners. Procrastinate, analayse, calculate all you want, Im getting a 4 yr payback with my 800$ Ng Bosch pilotless tankless. And only heating water I use.

[trader4]

"My guess is that one can remove heat from the heater exchanger of the furnace faster, than transfer it to water "

Just the opposite is true, which is why water is used as a coolant in everything from cars to nuclear reactors.

"Reason for this question is: Does it really make sense to insulate the water heater and hot water pipes, as some people do, in the winter ("blanket" type)? "

That depends. If where the water heater is located is a heated living space, then it's not going to make much difference one way or the other in the winter. But it will in the summer when you are trying to keep it cool. If the space is unheated, eg an unfinished basement, then better insulation is going to help year round.

[waldo2384]

Don't count on that payback. The Bosch heaters are very high maintenance. Maintenance costs will eat up all your gas savings and more. How do I know? I own one myself. It's nice when it works, but I do not recommend them at all.

[Tony Hwang]

Hi, What is initial cost of Bosch? How much hot water can it produce? Can it fill a Jaccui tub for a soaking bath in the evening? Tony

[m Ransley]

3 years and no breakdowns yet although it will cost alot to repair when it breaks my savings make up for what may happen or may not. You can say that about a 94% furnace with a VS DC motor or get an 80% unit and pay the utility co every month if you want to be negative. The coil is a 30 year design all copper unlike tanks which dont usualy last as long, they rust out

Cost depends on unit size, model and instalation difficulty. I paid

500? at menards for a 120 with piezo ignition, 2 D cells. It will put out hot water all day it is a demand unit . At 35f incomming I dont have it set on high to take a hot shower so it works. A unit has to be sized for your demand, mine is a one shower unit 117000 btu. The next grade up is 180000 btu or 2 shower unit. Takagi, Rinnai are the big companies. Takagi makes Bosches larger unit. I will never go back to a tank, or an 80% furnace.