Electric tankless water heater question on amperage

[miamicuse]

Property is in south Florida Miami, so the temperature rise is not as much as other locations.

I am looking to get a Stiebel Eltron Tempra 36. It will give me 4.5GPM with

55 degree rise. This will do what I need being a 2 bath house. The technical specs are:

Voltage 240 V Wattage 36 kW Amperage 150 A Minimum Required Circuit Breaker Size 3x60 A Recommended Wire Size 3x8 AWG Copper

I don't know if I have the proper electrical set up. I have four more unused slots in my electrical panel, there is an existing wire that goes to the current (to be replaced) hot water tank. My electric meter outside has this:

120/240V AC 3 WIRE MAX 200 AMP CL 200 * 240V * 3W * FM2S * TA30

Not sure what some of those mean. Can one tell if what I have matches up with what is needed? What electrical service do I need, if any?

Thanks,

MC

[miamicuse]

I rechecked the data sheet it says 150A.

It has several models:

Tempra 12 needs 50A, Tempra 20 needs 80 A, 24 needs 100 A, 29 needs 120 A and 36 needs 150 A.

Unless the document is in error? You can see the data here:

electrician

[Olaf]

36 kW = 36000

36000 / 240 = 150

Holy shit I think I'd rather have a tank if there was room.

electrician

[miamicuse]

Do I really have enough power or does it depend on what appliances may be drawing power at the same time (refrig, microwave, AC etc...)?

MC

[Harry]

Tankless water heaters come in electric and gas versions.

For an electric one - you need a very heavy power line directly to the unit. The unit is small but it calls for a lot of power when it snaps on.

The gas version is very nice - above two cubic feet. The ones we looked at cost around $2000 - but they tested out well. Very efficient - plenty of hot water when you want it.

Here is Tallahassee - the city own the electric and gas company. They offer a rebate of $450 for every water heater you convert from electric or gas - probably to cut down on peak loads. Since our home has two electric water heaters - we plan to convert them over to gas and get a $900 rebate - which will more than cover the conversion if we put conventional gas tank heaters in.

When the energy auditor was here - he figured the pay back for putting in two tankless gas heaters was over 10 years. If we chose the tank gas water heaters and the rebates - payback would be immediate.

I really like the tankless gas units - but right now will chose tank gas water heaters.

Harry

[Olaf]

It really depends on how many amps are available from the main panel. Even a

200 amp panel would not be able to handle that heater realistically unless there were no other heavy load 220 appliances (like a range, water heater, dryer, etc.) . My guess is that each 60 amp breaker would be hooked to separate heaters within the unit. the heater will turn on as many heaters as necessary to heat up to the 4.5 gpm.

[Olaf]

Oops, that was supposed to be a response to the OP. No biggie. :)

I can just imagine the lights dimming when someone jumps in the shower or fills the tub.

[Richard J Kinch]

You don't. This is a bad idea in general. It will be much cheaper and safer to use conventional water heaters.

[Edwin Pawlowski]

That should be 15A 3600 divided by 240 = 15

The meter does not matter, but the main breaker does. It is 200A? if so, you have plenty of power coming itn. The blank spots may be used. Depending on the existig wire, that may or may not be used. An electrician can tell you what size it is. It may be printed on the insulation.

You most likely have what you need for power. Your electrician will supply the proper breaker and wire. It would be a good idea to have him check it out before you buy the new heater though.

[Edwin Pawlowski]

Yes, I dropped a zero. Crap, that is a LOT of power. No, the OP does have enough power to the house to do that.

[RBM]

What this unit requires is three sets of two cables each. Each set connected to a 60 amp double pole breaker. Your 200 amp service would be fine ONLY if you didn't need electricity for the rest of your house

[Joseph Meehan]

You have already worked out the numbers and you know you are going to need some additional electrical work to use this puppy. They are nice, but they use an extreme amount of power for short periods of time. The cost of operation (ignoring cost of replacement and maintenance cost) is going to be less than the like cost of the usual tank type heater. The overall cost however is not likely to be less unless you have some other factors like limited space, unique usage cycles etc.