Using water heater for HP aux heat

Unknown

In what form? Isn't it lost in the form of heat? Where is it lost to? Doesn't it go into the water?

99%, where does the other 1% go? Please show your math...

Every bit of electricity used by the water heater element goes into heating the water.

Line losses before the meter aren't metered losses, they charge for those in a different fashion.

The BTUH conversion from watts is a good number. The science isn't flexible.

Noel

Tom Shekita

Using water heater for HP backup

My condo in MI was heated by a fan coil using a 100 gal Lochinvar water heater that also was domestic HW. It did a good job. In my house in GA I've got two 50 gal ele water heaters running in tandem to make sure I have lots of hot water. I wondered if I could use them as backup or aux heat for my heatpump instead of ele resistance coils. Would using the water heaters be any more efficent than using the ele strips as aux heat?

Jeff Lawrence_25

Well......

Electric heat, via water or air, is 100% efficient. The lower temps of the water coil wouldn't 'scorch' the air as much as the heat strips will.

While I can't exactly answer your question, I can point out one thing. Here in Georgia, we need heat for 4 to 5 months a year. That means the water in the lines will sit there with little or no circulation for 7 to 8 months. That makes that water a breeding ground for algae, bacteria, and bio-films. Then, when the circ for the back-up heat starts, it'll dump that long stagnant water back into the water heaters, possibly when you or someone in the house is taking a shower. That way, you may breathe in some of the garbage that has been breeding in the stagnant lines....

One of the reasons I point this out is that in MI, y'all needed heat for 6-7 months and the stuff didn't have as much time to accumulate.

Also, by your comment that you have electric WH's and a heat pump, you don't have NG available?

jp_2

water heater less efficient

if you use your water heat it will be far less efficient.

electrical heating may be close to 99% efficient, but then you have to add up the losses associated with the water, pipes get hot and lose, tank gets hot and loses....

strips heat only when you need heat.

also, as an heating element gets limed up, it needs to run hotter which lowers its efficiency.

Jeff Lawrence_25

electric

is 100% efficient. You ALWAYS get 3.41 BTU's per watt. The 'inefficiency' is in the way that heat transfers.

You are correct about the piping pump and tank losses, I forgot to mention that. Thanks for the correction.

jp_2

not 100% true

as far as I know, no type of energy transfer is 100% efficient.

transferring electricity into heat has to have inefficiencies,
there is certainly line loses along the wire lines, all wire has resistance and resistance is a loss.

but for practical disscussion, I prefer to say 99% efficient.

that 3.41 btu's per watt is just an estimate, maybe darn good estimate but still an estimate. not an exact science, as science is not exact.

don_185

Splitting hairs

One word..redundant

Tom Shekita

Jeff, your point about stagnant water had not occured to me. I can see your point and the potential for problems.

Jeff Lawrence_25

Thanks.

A lot of people don't see that.

[Deleted User]

stagnant line cooties

may be a moot point if you consider that something like legionella, the biggest? concern, is;

70 to 80 °C (158 to 176 °F) - Disinfection range
At 66 °C (151 °F) - Legionellae die within 2 minutes
At 60 °C (140 °F) - Legionellae die within 32 minutes
At 55 °C (131 °F) - Legionellae die within 5 to 6 hours
50 to 55 °C (122 to 131 °F) - They can survive but do not multiply
20 to 50 °C (68 to 122 °F)- Legionellae growth range
35 to 46 °C (95 to 115 °F) - Ideal growth range
Below 20 °C (68 °F) - Legionellae can survive but are dormant