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Old 12-05-2008, 02:33 PM   #1
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Tankless water heater


would like to install new tankless water heater it needs 3#8 awg copper wire with 3- 40 amp breakers. need to run about 75 feet of wire. My question is should i install a sub panel or just run the # 8 wire from my main panel. if I install a sub panel what size wire should i use. Thanks Crabman

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Old 12-05-2008, 02:39 PM   #2
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If you have enough room in your panel, there's no need to install a subpanel.

I guess it's too late to talk you out of installing a tankless electric, right?

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Old 12-05-2008, 02:45 PM   #3
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I guess it's too late to talk you out of installing a tankless electric, right?
You should still try, so I can read it
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Old 12-05-2008, 02:48 PM   #4
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would like to install new tankless water heater it needs 3#8 awg copper wire with 3- 40 amp breakers. need to run about 75 feet of wire. My question is should i install a sub panel or just run the # 8 wire from my main panel. if I install a sub panel what size wire should i use. Thanks Crabman
You will need 6 #8 Cu wires plus a #10 ground. Do you have at least a 200A service that is way underloaded?
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Old 12-05-2008, 02:55 PM   #5
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No wants wrong with tankless
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Old 12-05-2008, 02:57 PM   #6
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You should still try, so I can read it
Well, like Househelper alluded to, it's a large enough load to have a real chance of tripping your main on a 200 amp service. Forget about it on less than 200 amps.

The energy gains are often overstated, it might take you 20 years to pay back the increased initial cost. Every time you turn on the tap you'll have to run extra water waiting for the water to get hot.

Consumer reports also says that tankless electric are not going to perform in a way most people consider acceptable, and they refuse to even review them on those grounds.
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Old 12-05-2008, 03:24 PM   #7
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Tankless water heater


I like electric water tanks (vs tankless) as they are usually cheap and far more sealed and super insulated than others, having almost no loss (they also save energy by not requiring a flue/hole in your house nor have an uninsulated flue running through the center).

I had a tankless oil boiler for hot water and cost me $45/month for hot water (when oil was $3/gallon). I decided time to buy a solar DHW system including the special super insulated hot water tank w/elec backup. After installing the tank and shutting off my boiler without even having done the solar to the new water tank my electric bill only increased $22/month vs. the $45/month for the tankless oil boiler. It saves on heating too since my boiler used house air and sent it out the flue my elect water tank doesn't have a flue.

Had I realized a super insulated electric tank was that good (having almost no loss and being able to hold its heat for days) I'd likely have just done the tank part and skip the solar since at best hooking in my solar will save at most $22/month (but solar is cool!!!). If it's not too late, you should really consider instead a super insulated elec tank vs tankless route.

Last edited by Piedmont; 12-05-2008 at 03:42 PM.
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Old 12-05-2008, 03:26 PM   #8
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Yeah if you want to do green stuff there's better places to spend your money than tankless water heaters.
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Old 12-05-2008, 03:36 PM   #9
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Tankless water heater


Tankless electrics are a joke. Plain and simple. The savings are minimal and the burden on the electrical system is tremendous!

Depending on your house, a monster that takes three 240v-40a circuits may push you to have to upgrade to a 320a service.
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Old 12-05-2008, 10:30 PM   #10
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I researched replacing my natural gas heater with a 'tankless' natural gas heater and its not worth doing in this case either!
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Old 12-06-2008, 06:27 AM   #11
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Tankless electrics are a joke. Plain and simple. The savings are minimal and the burden on the electrical system is tremendous!

Depending on your house, a monster that takes three 240v-40a circuits may push you to have to upgrade to a 320a service.
Bingo,,,we have a winner.

Electric tankless water heaters need a small nuclear reactor in the back yard to make them work.

The high end tanked water heaters are 96% efficient and are a lot easier to wire.

Get a large tanked water heater and set the temperature for lower heat levels and you will see lots of savings and not have to invest in nuclear.

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