Help with electric tank water heater selection

[lhgrappler]

Family of 6, who love hot showers, 3 bathrooms. High likely hood of people showering at the same time.

We are out in the country and need to go electric. We are completely renovating this house, so we are starting from scratch. I found this 80 gallon tank that I was planning on using (converting down to 240 volt), but now I'm having second thoughts. I already purchased it though, and it is non-returnable. So, I'd have to sell it likely for less than I bought it for. I had looked at Hybrids before buying it, but they were a lot of bad reviews, making me think the technology isn't quite there yet.

I'm worried about recovery time, and electrical costs. Would we be better off doing a 50 gallon with the cash acme tank booster?
Will the difference in electrical bills between 50 and 80 gallon be big?

Thanks

 

[Breplum]

I'm no electrical guy but that 80 gal is made for 277 V, so, it is not made for residential power.
hopefully a smarter contribution will follow. I'll be curious.

 

[Sponsor]

 

[lhgrappler]

I'm no electrical guy but that 80 gal is made for 277 V, so, it is not made for residential power.
hopefully a smarter contribution will follow. I'll be curious.

It can be converted to 240, or 208. We would be doing 240v

https://www.supplyhouse.com/AO-Smith-100293212-Kit-Conversion-Lte-dce-4500w240v

 

[wwhitney]

The spec sheet says it has two 6.1 kW / 277V single phase elements that may operate simultaneously.

6100W @ 277V becomes (240/277)^2 * 6100 = 4580W @ 240V. So the unit would require a minimum 240V 25A circuit if the two elements are interlocked to not run simultaneously, or a 50A circuit if they can run simultaneously.

Cheers, Wayne

 

[Reach4]

A drain heat recovery system would help match your needs. Many long showers.

Drain Water Heat Recovery system design

Normally, this would be pretty simple, but my system is not that simple, so here goes. I have an open radiant floor heat system, so its combined with my DHW. Yes, I'm well aware of everyone's concerns about legionaires, etc, and have addressed them all with redundancy in both temperature and...

www.terrylove.com

It should save electricity, but might even let you get by with a smaller WH.

 

[WorthFlorida]

Family of 6, who love hot showers, 3 bathrooms. High likely hood of people showering at the same time.

We are out in the country and need to go electric. We are completely renovating this house, so we are starting from scratch. I found this 80 gallon tank that I was planning on using (converting down to 240 volt), but now I'm having second thoughts. I already purchased it though, and it is non-returnable. So, I'd have to sell it likely for less than I bought it for. I had looked at Hybrids before buying it, but they were a lot of bad reviews, making me think the technology isn't quite there yet.

I'm worried about recovery time, and electrical costs. Would we be better off doing a 50 gallon with the cash acme tank booster?
Will the difference in electrical bills between 50 and 80 gallon be big?

Thanks

 

[WorthFlorida]

I installed two cash acme tank booster and they work really well. At my church we removed a 80 gallon electric installed 1985. We replaced it with a 50 gallon electric with a tank booster. This water heater is mainly used for the parish hall kitchen. Lots of washing during fish frys.

The other one was at my son's house. Two teenage girls! Same here, replaced a 40 gallon tank with the temp set to high to compensate for lack of hot water. Performing now with no issues.

The power consumption between a 50 & a 80 gallon unit is nearly the same as you use water. if you have to heat 20 gallons of cold water, it's the same power needed in either tank. The extra cost is the 20 gallons to get it to the set temperature and standby lost.

A 50 gallon with the tank booster is equivalent to a 90 gallon tank.
The recovery rate for either unit is the same, both use 4500 watts heating elements @240 volts. If you find the recovery rate is not good enough, you can replace the elements with 5500 watt units. You can also buy WH with factory installed 5500w elements. Just be sure your electric panel can handle the load. A big factor in the recovery rate is the inlet water temperature. Florida it's 75 degrees or warmer, VT is 42 degrees.

50 gallon with a tank booster would be my choice.

 

[Fitter30]

How many watts are the 277 vac elements? Could use a buck and boost transformer need to know the watts for sizing. Brand and model of heater?

 

[John Gayewski]

If you already have the 80 gal tank use it. There's no reason not to. Your heat loss on an 80 gal tank vs a 50 isn't going to be the much different.

 

[wwhitney]

How many watts are the 277 vac elements?

See post #4.

Could use a buck and boost transformer need to know the watts for sizing.

That would much more complicated and expensive than changing the elements, which isn't even necessary as per post #4.

Brand and model of heater?

See the link in the OP.

Cheers, Wayne

 

[Fitter30]

6.1 kw= 20813 btu 22 amps @ 277
4.5 kw= 15354 btu 18.75 amps @ 240
26.2% less watts
7.5 kva step up transformer 240 to 277vac

Step up transformer 240v to 277v | eBay

This Electric Power Transformer is designed for AC to AC conversion with a primary voltage rating of 240V and a secondary voltage rating of 277V. It has a primary current rating of 46A and a secondary current rating of 46A. The transformer has a step-up conversion function and a turns ratio of...

www.ebay.com

 

[WorthFlorida]

What size is your breaker panel? Is it planned for an upgrade? If you get 200 amp panel you can go with a tankless. You may need three 240 volt breakers. The prices have dropped quite a bit and they can be sized to your needs. A 27kw should work delivering over 5 gallons a minute. There are charts for this depending on inlet cold water temperature. The big savings is no standby lost.

 

[Bannerman]

The spec sheet says it has two 6.1 kW / 277V single phase elements that may operate simultaneously.

Residential WHs do not use thermostats that permit the elements to operate simultaneously.

Hot water is less dense than cold, so hot water will rise to the top of the tank.

Under normal use, the lower element will continue to be activated when the temperature near the top of the tank remains above the upper thermostat temperature setting, thereby allowing the entire tank volume to be heated gradually.

When the temperature of the water near the top (where the upper thermostat is located) is below the set point, only the upper element will be activated, thereby heating the smaller volume of water located close to the top, which will reduce the time before hot water will exit the WH after the tank is depleted. Once the water temperature near the top rises above the set point, then the upper element will be shut off and lower element will become activated, to continue to heat the larger volume of cold water closer to the bottom.

For both elements to operate simultaneously, will require much larger wiring capable of the appropriate higher amperage than normally supplied to a residential WH, and a new, double pole breaker, capable of supplying that higher amperage @ 240 volts.

If each element consumes 5000 watts @ 240 volts, that equals 21 amps (25 amp wiring & breaker minimum) when either element is active. For 2 - 5K watt elements to operate simultaneously, will require wiring and a breaker capable of at least 50 amps.

 

[wwhitney]

Residential WHs do not use elements that operate simultaneously.

OK, but as a unit configured to operate on 277V, the water heater referenced in the OP is obviously not a residential model. Its spec sheet from the link in the OP indicates that the two elements may be configured to operate simultaneously.

Cheers, Wayne

 

[Bannerman]

OK, but as a unit configured to operate on 277V, the water heater referenced in the OP is obviously not a residential model. I

Yes, that unit is specified as intended for light commercial.

To obtain 277 volts AC, will require utilizing 1 phase of a 3-phase power supply. While 3-phase power supplies are only starting to become available in residential installations (mainly due to faster charging speeds possible for EVs), the vast majority of North America homes are equipped for only 240 volts, single phase AC.

Supplying 240 volts to a 5K watt, 277 volt element is likely possible, but that will reduce the heating output to about 4500 watts. Since 4500 watts @ 240 volts equals 18.75 amps, to operate both elements simultaneously, will continue to require higher amperage wiring and a higher capacity breaker than would be required to supply most regular residential WHs.

 

[wwhitney]

Supplying lower voltage to a 5K watt element is likely possible, but that will reduce the heating output to about 4500 watts. Since 4500 watts @ 240 volts equals 18.75 amps, to operate both elements simultaneously will continue to require higher amperage wiring and a higher capacity breaker than would be requiredto supply most regular residential WHs.

Yes, but the "kit" in post #3 for 240V operation just consists of instructions to rewire the controls so the two elements do not operate simultaneously, along with an updated sticker. And no change is made to the elements.

Operating an element rated at 6100 kW elements at 277V at the reduced voltage of 240V will give 75% of the power output (the square of 240/277), or 4580W. Which is close to a standard residential water heater, and will be fine on a typical 30A / 240V residential water heater circuit.

Cheers, Wayne

 

[Bannerman]

, but the "kit" in post #3 for 240V operation just consists of instructions to rewire the controls so the two elements do not operate simultaneously,

Correct. When I read the OP's initial comments, I suspected he was possibly planning to run both elements simultaneously.

I hed not seen your reply in post #4 when I started my reply, or when I first replied to you. After refreshing the page then seeing post #4 after I posted, I would not have bothered posting, as I basically repeated the advice you had already provided.

 

[Sedin26]

Correct. When I read the OP's initial comments, I suspected he was possibly planning to run both elements simultaneously.

I hed not seen your reply in post #4 when I started my reply, or when I first replied to you. After refreshing the page then seeing post #4 after I posted, I would not have bothered posting, as I basically repeated the advice you had already provided.

I have a Bradford White residential water heater and the manual specifically calls out the ability to operate both elements simultaneously. I've seen the same in various other Bradford White manuals - I don't know about other brands. You can order them ready for it or just change the wiring a bit to suit this setup.

You don't go with one larger breaker and wiring but actually use two breakers and two wire runs to the water heater. So, if you went with 5500w elements, you would use two 30amp breakers and 10 gauge wire for each, though I might go for 8 gauge just for that extra headroom.

Between doing that and adding a thermostatic mixing valve, you get significant improvement in recovery time and availability of hot water. I prefer this method because a big or decent sized tankless is a lot more demanding on the electrical service and there are also various localities that are starting to add demand charges on residential services.

 

[Fitter30]

6100 w element @277
5246 w @ 240 17888.86 btu
5500w. 18755 btu

 

[wwhitney]

6100 w element @277
5246 w @ 240

No, the power dissipated by a resistive element scales with square of the voltage, not linearly. P = I * V, and V = I * R, so P = V * V / R for a fixed R.

(240/277)^2 = 0.75, which means an element rated 6100W @ 277V will be rated 6100W * 0.75 = 4575W @ 240V.

Cheers, Wayne