Can this gas WH be replaced with electric?

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LTLFTcomposite

Well-known member
Joined
Apr 23, 2010
Messages
4,780
Location
Central FL
A family member's house currently has a gas WH that is quite old and I'd like to replace it before it fails. I'm trying to decide if I can go electric. The water heater is the only thing that currently runs on natural gas in the house, so it would be a simplification to get rid of it. Also the electric seems like less to worry about, no CO, flame etc, cheaper and easier to install, and from an environmental perspective the utility co is increasing renewable in the mix.

The dryer was on a three wire circuit which I upgraded to four wire for safety, that leaves an unused #10/3 from the panel that would be perfect for the water heater. The concern is whether the service supports it. The main is a 100A breaker, the panel is rated for 125A. I'm not sure what the wire size is on the service, presumably sufficient for 100A.

One of those on line load panel calculators came up with 129A. I did my own calculation and it looks like you'd have to have everything in the house on including all four stove elements and the oven before it would be a problem, but I suppose it's possible someone will be doing wash and cooking thanksgiving dinner and running two hair dryers. It seems like it would all be fine in practice but maybe this is just a full stop until I get an electrician in to evaluate the incoming service, or just go with another gas water heater. I did look at a hybrid water heater but it looks like they have backup resistance elements so no real help there. Cost is an issue as well. There are conventional electric water heaters with a little lower wattage (3800 instead of 4400 or 5500) so I figured on that.

AC 3600
WH 3800
dryer 5600
washer 800
fridge 700
dishwasher 700
small appliances 3000
misc 1000
total w/o range 19200

range 7680
total w/range 26880

100A 24000
80% 19200
 
You could certainly switch to electric. However electric, even at off peak rates will be more expensive than the cost of gas, but taking in to account you could ditch the monthly gas hook up fee it might be a wash. On the load side a Heat Pump or hybrid water heater would be close to the same cost as natural gas. You can disable the resistance part and only use the heat pump, the problem with that is recovery time. With two people and an 50+ gallon tank no problem, more people or teenagers taking showers and it wouldn't work.

Along those same lines in the first house (cabin) we owned had a 5 gallon 120v water heater. I put in a 80 gallon tank but the house only had a 60 amp service. So I disconnected the upper element and wired it so only the lower element would run, the 4800w 240vac lower element and running at 120vac pulled about 1200w. It took 5 hours to recover from one shower but with only my wife and I at the time it worked.

So it depends on how your going to use it. Oddly enough it is similar to using a car on L1 or L2.
 
BrockWI said:
You could certainly switch to electric. However electric, even at off peak rates will be more expensive than the cost of gas, but taking in to account you could ditch the monthly gas hook up fee it might be a wash. On the load side a Heat Pump or hybrid water heater would be close to the same cost as natural gas. You can disable the resistance part and only use the heat pump, the problem with that is recovery time. With two people and an 50+ gallon tank no problem, more people or teenagers taking showers and it wouldn't work.

Along those same lines in the first house (cabin) we owned had a 5 gallon 120v water heater. I put in a 80 gallon tank but the house only had a 60 amp service. So I disconnected the upper element and wired it so only the lower element would run, the 4800w 240vac lower element and running at 120vac pulled about 1200w. It took 5 hours to recover from one shower but with only my wife and I at the time it worked.

So it depends on how your going to use it. Oddly enough it is similar to using a car on L1 or L2.
Funny you mention that, I had previously thought of repurposing that 10/3 for an EVSE, but vehicle electrification in the family is on hold for a bit as the financial situations and technology/costs align. The dryer is in the garage and the newly installed 14-30 is convenient if someone does happen by with a Tesla. Curiously that old 10/3 is red-black-white, I don't think they even make that any more - I assumed it's ok to wrap the white wire with green tape at both ends and use it for an EGC. Running the water heater on 120v is a Florida post-hurricane trick, but only as a temporary hookup, not sure I'd want to do that as a permanent setup.
 
Operating costs depend upon locations and energy providers. In my case, conventional electric water heater using off-peak power is much cheaper than natural gas. It would probably be about the same cost as gas considering peak rates or non time-of-use rates. Heat pump type would use less power so energy costs would be even lower.

Since electrical and building codes typically allow diversity factors to be taken into account for load calculations, your 100-ampere panel may be adequate to add an electric water heater. You need an evaluation based upon your local codes.
 
Gerry out of curiosity what do you pay for gas / elect? Ours is $.061 for off peak electric and $.22 on peak and $1.00 critical peak. Our natural gas ranges from $.25 a therm to $1.10 a therm right now it is $.55. For us natural gas has to be above $1.40 a therm to match the $.061 of resistance off peak and we have never hit that, yet...
 
Now I'm seeing some resources that suggest the 100A service may be fine... going back to the 100% for the first 10kW and 40% for the rest. IIRC that rule is what Wayne Whitney pointed out when I was asking about putting an EVSE in a vacation rental.
 
I've not actually studied Article 220 in the NEC on load calculations, but I do know that almost always the optional method described in Part IV of the article (starting at 220.80) is almost always a lower number. So be sure your calculator is using the optional method. The result is still quite conservative.

Cheers, Wayne
 
Consider a heat pump water heater. Sized right and in FL you will not likely need to use it in hybrid or full electric resistance heating mode. Most new heat pump water heaters allow one to operate in "heat pump only" mode which will shutout backup resistance elements. But building codes/inspectors will still likely assume the device at it's highest potential power draw.

We replaced our 50G natural gas water heater about 1.5 years ago with a 65G heat pump water heater. In "heat pump only" mode ours only uses 325-425W. In that mode when you run out of hot water, that's it, no resistance heating, just cold water.

We're a family of 4 and each take two showers a day, we do the usual laundry and run a dishwasher. No problems there. We recently had 2 in-laws here in the middle of (our mild) winter and cranked the heat setting up a few degrees and still no cold showers.
 
BrockWI said:
Gerry out of curiosity what do you pay for gas / elect? Ours is $.061 for off peak electric and $.22 on peak and $1.00 critical peak. Our natural gas ranges from $.25 a therm to $1.10 a therm right now it is $.55. For us natural gas has to be above $1.40 a therm to match the $.061 of resistance off peak and we have never hit that, yet...

It looks like natural gas here in Phoenix is cheaper than what I guessed based upon the last time I had gas service. The current rate is $1.05/therm (includes $0.05/therm credit for fuel cost adjustment this month) and there is a $10.70 monthly service charge (not including taxes). I said I would never live in a gas neighborhood again after the present company bought the gas division from the electric utility and the residential gas cost went up 50% in one year. At that point, it was way cheaper to use electricity for everything. I have not checked gas prices lately so I was surprised to see they are about even with my electric costs (when I consider that the electric water heater is 100% efficient and a percentage of therms goes up the exhaust with a gas unit). My off-peak is between $0.04 and $0.05/kWh, depending upon time of year and fuel cost adjustments. My on peak rate includes a demand charge and I have a load controller to minimize the peak demand so energy cost is between $0.06 and $0.07/kWh (depending upon time of year and fuel cost adjustments).

I second the recommendation to get a heat pump type. I wanted to put one in when I had to replace the tank the builder installed, but they were not in stock locally and I could not wait two weeks.
 
wwhitney said:
I've not actually studied Article 220 in the NEC on load calculations, but I do know that almost always the optional method described in Part IV of the article (starting at 220.80) is almost always a lower number. So be sure your calculator is using the optional method. The result is still quite conservative.

Cheers, Wayne

As always thanks for the reply.

Yes, I got into the whole thing about the "optional method" and low and behold the answer on the spreadsheet came out at exactly 100A. That's using the commonly available 4500W heaters, not the 3800W. The only part I'm not sure I did right was the range... it says to use the nameplate rating, which I neglected to check. This is your garden variety electric range which apparently has a nameplate rating around 11-12kW but for whatever reason calculations commonly peg them at 8000W. I'm not sure which number I should be using in the optional method calculation. They say these can be installed on 40A circuits, so the 8000 number makes sense.
 
iPlug said:
Consider a heat pump water heater...
GerryAZ said:
I second the recommendation to get a heat pump type...
It would be nice, but that's an extra grand not laying around. This house is not high occupancy, payback would probably be three years minimum. More complex installation too, having to add the drain line.

We had a neat system at a house quite some time back - a heat recovery unit on the central AC unit. That thing made crazy hot water 9-10 months out of the year when we did even have the power turned on to the water heater. Surprised those never became more popular. If you think about it why have a second heat pump, you already have one! Purportedly made the AC more efficient but that's just theory.
 
If the gas water heater is the only gas appliance I would get rid of it and turn off gas service if the person doesn't want additional gas appliances.
 
Oilpan4 said:
If the gas water heater is the only gas appliance I would get rid of it and turn off gas service if the person doesn't want additional gas appliances.
That's the idea... simplify things, outsource the combustion of natural gas to the power company.
 
I said no to natural gas.
Natural gas is a great thing and hydraulic fracturing made it possible reduce the pollution put off by power generation by eliminating coal fired power plants.
For me it was all about the $, the surcharge out on the coop is high.
Imo it's not worth the install cost which would run around $2,000 unless I also at installed a gas furnace, gas water heater, gas dryer, gas range.
So total cost would be up around $7,000 if I did all the appliance change overs my self.
I would have to have a contractor licensed gas certified plumber pull permits to do the initial install to the house. Can't get around that part.
 
Natural gas is a great thing and hydraulic fracturing made it possible reduce the pollution put off by power generation by eliminating coal fired power plants.

Replacing it with contaminated wells and even whole aquifers. This is why I'm pushing for us to get a ground source heatpump instead of a dual air-source/NG heating system.
 
Where?
I have only ever been able to find a hand full cases of contaminated ground water due to fracking.
Not bad considering nearly a million fracking jobs have been completed.
I live in a fracking heavy area and have an excellent water well.

If the fracking boom that started in the mid 2000s, that was extended by the fracking ban scare all through the Obama administration years never happened then natural gas would probably cost around $12 to $20 per million BTUs. Making it prohibitively expensive for most power generation.
The Natural gas power generation market share would have shrank to almost nothing and coal would still make nearly half our nations electricity.

The ground source geothermal is nice I would like to do it.
But first I have a water well and rain water system to install to eliminate my $55 per month coop water bill.
And put up solar panels.
While planting an orchard.
 
The power company is going to do what the power company is going to do, but lately that appears to be increasing renewables in the mix. If we put in another gas water heater that fossil fuel consumption will be "locked in" to the mix.
Really switching from a gas to an electric water heater is no different from switching to an EV from an ICE other than maybe the scale. Oh sure, there will be the trolls saying now we're heating water with coal, but if you ascribe to the greening grid theory it still should be a better way to go.
 
I considered a heat pump WH to replace our gas unit a year or so ago. Energy costs seemed about the same or even a little lower with the heat pump. BUT... I checked around and repairs for a heat pump unit are relatively frequent (most gas or resistance electric units never need service in their 10 year typical life span). And, when a heat pump WH needs fixing, repairs are typically expensive. The idea is great, but I think manufacturers need to increase reliability for widespread heat pump adoption to occur.
 
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