On demand electric water heaters

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wireguy8169

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Southern Maine
I read they are less efficent than the gas version, but are they still more efficent and less costly to run than an electric water hear of the storage type? Can anyone give some insight on this...thanks

I am aware that they are typically more exspensive to buy but will it pay off in the end?
 
I have installed many electric on demand for a contractor. I cant remember the brand he uses.
Customers were unhappy with anything but a 3 element unit for a small house.
I believe it took 3 40A circuits and had a nameplate of 112.5 amps.
Usually a single element one (40A circuit) will handle a single sink with low useage.
If you do a whole house one with less than 3 elements run a 1" or 1-1/4" conduit to the panel so if you need to pull more 40A`circuits later you can. People are usually unhappy with the 2 element ones for a whole house. If you buy the correct base unit a single can be upgraded to a three so If the customer is unhappy it is less of a service call to upgrade the unit.
Cheers
 
tortuga said:
I have installed many electric on demand for a contractor. I cant remember the brand he uses.
Customers were unhappy with anything but a 3 element unit for a small house.
I believe it took 3 40A circuits and had a nameplate of 112.5 amps.
Usually a single element one (40A circuit) will handle a single sink with low useage.
If you do a whole house one with less than 3 elements run a 1" or 1-1/4" conduit to the panel so if you need to pull more 40A`circuits later you can. People are usually unhappy with the 2 element ones for a whole house. If you buy the correct base unit a single can be upgraded to a three so If the customer is unhappy it is less of a service call to upgrade the unit.
Cheers
Click to expand...

Yeah the one I am going to install is a three element unit forget the Manufacture. The customer is an Energy Auditor and swears by them, just wanted to get some other input I will install whatever they want but if its something that is the real deal maybe I will recommend them if asked.
 
wireguy8169 said:
I read they are less efficent than the gas version, but are they still more efficent and less costly to run than an electric water hear of the storage type? Can anyone give some insight on this...thanks

I am aware that they are typically more exspensive to buy but will it pay off in the end?
Click to expand...

They should be 100% efficient and a gas unit might be in the order of 90% efficient, but gas heat is generally cheaper than electric heat. I would expect a gas unit to be cheaper to run, but more expensive to buy.

The on demand units do not waste heat from 50 gal or so of hot water just waiting to be used.
 
IMO on demand units will never pay for them selves. Standby losses on electric tanks are very low because the tank is completely encapsulated with foam (unlike gas units that have substantial flue loss). If you need endless hot water, then of course an on demand may be for you.

Edit: just realized the OP is 9 years old.
 
electrofelon said:
IMO on demand units will never pay for them selves. Standby losses on electric tanks are very low because the tank is completely encapsulated with foam (unlike gas units that have substantial flue loss). If you need endless hot water, then of course an on demand may be for you.

Edit: just realized the OP is 9 years old.
Click to expand...
Pretty interesting topic from a 9 year old.:)

I think a few old threads got new life during the forum software changes.
 
tortuga said:
I have installed many electric on demand for a contractor. I cant remember the brand he uses.
Customers were unhappy with anything but a 3 element unit for a small house.
I believe it took 3 40A circuits and had a nameplate of 112.5 amps.
Usually a single element one (40A circuit) will handle a single sink with low useage.
If you do a whole house one with less than 3 elements run a 1" or 1-1/4" conduit to the panel so if you need to pull more 40A`circuits later you can. People are usually unhappy with the 2 element ones for a whole house. If you buy the correct base unit a single can be upgraded to a three so If the customer is unhappy it is less of a service call to upgrade the unit.
Cheers
Click to expand...
Does the bold mean 3 separate 40 amp single pole breakers? (120V)
Or is that 3 40 amp double pole breakers? (240V)
How about a double pole 125A breaker? (240V)
Either way, that's a lot of juice for a home electrical panel.
 
powerpete69 said:
Does the bold mean 3 separate 40 amp single pole breakers? (120V)
Or is that 3 40 amp double pole breakers? (240V)
How about a double pole 125A breaker? (240V)
Either way, that's a lot of juice for a home electrical panel.
Click to expand...
27kW - so 3 40 amp 240 volt circuits.

With an on demand water heater you need to heat water from maybe as cold as 55 degrees to desired level of 105-120 degrees at the rate it is flowing. Storage tank heaters already have a reserve of hot water and don't need such high demand from source, but must have time to recover. Disregarding losses during storage or in the pipes, it takes the same kWhrs just over different amount of time in each case.
 
Thanks,
So you would need a minimum 200 amp panel at 240V to allow for the other house loads.
Not gonna fly in the older houses with 100 amp panels or less.
 
Every time somebody calls me up about installing circuits for one of these water heaters I have to explain to them that they do not have sufficient capacity in their electrical panel. (Except the rare 200 amp panel and single element WH combo.) I actually had a middle unit attached condo owner present me with a water heater that drew more amps than his entire 100 amp panel. There was no way to upsize a middle unit panel. I steer all these people to gas units that mount outside and use a fraction of an amp on a 15 amp circuit to light the pilot.
 
I'm still using an old (circa 1982) solar water heating system. It has 125 gallons of storage and is backed up with natural gas for the times it is cloudy for a number of days. Water is heated by two 5x10 roof panels and drains back to the heat exchange tank at night. It's a beautiful thing.
 
My son in law wanted one, so I put in one, his poco provides live usage records online, so he is able to monitor it closely. Him, my daughter and my two grandsons. No savings, but no cold water either though. Probably where some savings could be found is a weekend retreat where it is only used a couple times a week. Around here, anything built in the past 30 years are 200 amp or larger service, tract homes may be 150, but there are virtually none of those within a 30 mile radius.
 
My friend in PSE-land has multiple units on sinks. They run only to get instant hot water. If you are using more than a few gallons the water from the main tank makes it to the sink and the instant off turns off.
 
Open Neutral said:
My friend in PSE-land has multiple units on sinks. They run only to get instant hot water. If you are using more than a few gallons the water from the main tank makes it to the sink and the instant off turns off.
Click to expand...

+1
Son's office has small 30A units for each 2 bath sinks. 1.5 gal per minute or so hot water. Small, reliable - installed 8 years ago no troubles yet.
 
Open Neutral said:
My friend in PSE-land has multiple units on sinks. They run only to get instant hot water. If you are using more than a few gallons the water from the main tank makes it to the sink and the instant off turns off.
Click to expand...
Not so much wrong with that sort of use, you don't need a 27kW unit for that application as you are only using it to heat from room temp to desired temp and usually at a fairly low flow rate.
 
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