User avatar
LTLFTcomposite
Posts: 4661
Joined: Fri Apr 23, 2010 6:06 pm
Delivery Date: 10 Dec 2011
Leaf Number: 5926
Location: Central FL

Can this gas WH be replaced with electric?

Mon Jan 21, 2019 8:44 am

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
LTL
White 2012 SV delivered 10 Dec 2011 returned 25 Nov 2014 replaced with stopgap ICE Sentra
[35 months] [35K miles] [9 Bars]
2013 Volt replaced after 36 months/30k miles with ICE Rogue
2016 SV-adjacent May 2016 lost 4th bar March 2018

BrockWI
Posts: 754
Joined: Fri Mar 28, 2014 6:28 am
Delivery Date: 28 Mar 2014
Leaf Number: 423875
Location: Green Bay, WI.
Contact: Website

Re: Can this gas WH be replaced with electric?

Mon Jan 21, 2019 9:13 am

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.
3 kw solar pv - XW6048 - eight L16's
4 ton GSHP - 1 ton ASHP
2003 VW TDI 200k miles - 52 mpg lifetime
EVSE level 2 - Clipper Creek HSC-40
2013 S model with QC package Mar of 2013
lost first bar @ 72k
@82k miles - 58.98Ahr - 90SOH - 87.70Hx - 256GID

User avatar
LTLFTcomposite
Posts: 4661
Joined: Fri Apr 23, 2010 6:06 pm
Delivery Date: 10 Dec 2011
Leaf Number: 5926
Location: Central FL

Re: Can this gas WH be replaced with electric?

Mon Jan 21, 2019 9:43 am

BrockWI wrote: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.
LTL
White 2012 SV delivered 10 Dec 2011 returned 25 Nov 2014 replaced with stopgap ICE Sentra
[35 months] [35K miles] [9 Bars]
2013 Volt replaced after 36 months/30k miles with ICE Rogue
2016 SV-adjacent May 2016 lost 4th bar March 2018

GerryAZ
Gold Member
Posts: 2096
Joined: Mon Nov 22, 2010 6:47 pm
Delivery Date: 12 Jun 2011
Location: Phoenix, AZ

Re: Can this gas WH be replaced with electric?

Mon Jan 21, 2019 10:26 am

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
Silver LEAF 2011 SL rear ended (totaled) by in-attentive driver 1/4/2015 at 50,422 miles
Silver LEAF 2015 SL purchased 2/7/2015

BrockWI
Posts: 754
Joined: Fri Mar 28, 2014 6:28 am
Delivery Date: 28 Mar 2014
Leaf Number: 423875
Location: Green Bay, WI.
Contact: Website

Re: Can this gas WH be replaced with electric?

Mon Jan 21, 2019 11:23 am

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...
3 kw solar pv - XW6048 - eight L16's
4 ton GSHP - 1 ton ASHP
2003 VW TDI 200k miles - 52 mpg lifetime
EVSE level 2 - Clipper Creek HSC-40
2013 S model with QC package Mar of 2013
lost first bar @ 72k
@82k miles - 58.98Ahr - 90SOH - 87.70Hx - 256GID

User avatar
LTLFTcomposite
Posts: 4661
Joined: Fri Apr 23, 2010 6:06 pm
Delivery Date: 10 Dec 2011
Leaf Number: 5926
Location: Central FL

Re: Can this gas WH be replaced with electric?

Mon Jan 21, 2019 11:51 am

Holy cow, here in FL electricity is like 11 cents/kWh... and people complain about it.
LTL
White 2012 SV delivered 10 Dec 2011 returned 25 Nov 2014 replaced with stopgap ICE Sentra
[35 months] [35K miles] [9 Bars]
2013 Volt replaced after 36 months/30k miles with ICE Rogue
2016 SV-adjacent May 2016 lost 4th bar March 2018

User avatar
LTLFTcomposite
Posts: 4661
Joined: Fri Apr 23, 2010 6:06 pm
Delivery Date: 10 Dec 2011
Leaf Number: 5926
Location: Central FL

Re: Can this gas WH be replaced with electric?

Mon Jan 21, 2019 11:55 am

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.
LTL
White 2012 SV delivered 10 Dec 2011 returned 25 Nov 2014 replaced with stopgap ICE Sentra
[35 months] [35K miles] [9 Bars]
2013 Volt replaced after 36 months/30k miles with ICE Rogue
2016 SV-adjacent May 2016 lost 4th bar March 2018

wwhitney
Posts: 751
Joined: Sat Jul 17, 2010 10:10 am
Delivery Date: 01 Apr 2011
Location: Berkeley, CA

Re: Can this gas WH be replaced with electric?

Mon Jan 21, 2019 6:26 pm

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

iPlug
Posts: 264
Joined: Thu Apr 28, 2016 6:47 pm
Delivery Date: 25 Apr 2016
Location: Rocklin, CA

Re: Can this gas WH be replaced with electric?

Mon Jan 21, 2019 6:35 pm

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.
'19 Model 3 SR+ (own), '16 Leaf SV (leased), '12 Plug-in Prius (sold 3/19), 11.43kW Solar PV (16MWh/yr real production), 20.5 SEER/13.0 HSPF ducted air-source heat pump, 3.70 UEF heat pump water heater, Induction Cooktop, Variable Speed Pool Pump

GerryAZ
Gold Member
Posts: 2096
Joined: Mon Nov 22, 2010 6:47 pm
Delivery Date: 12 Jun 2011
Location: Phoenix, AZ

Re: Can this gas WH be replaced with electric?

Mon Jan 21, 2019 6:54 pm

BrockWI wrote: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.
Gerry
Silver LEAF 2011 SL rear ended (totaled) by in-attentive driver 1/4/2015 at 50,422 miles
Silver LEAF 2015 SL purchased 2/7/2015

Return to “Off-Topic”