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Electric/propane water heater?

ericfx1984

ericfx1984

Solar Enthusiast
Joined
Oct 10, 2021
Messages
741
I have been thinking, propane is a great way to heat water... But if I have excess solar power, which happens a lot in the winter, I might want to heat with solar...

But I can't seem to find a water heater that can do this...

Anyone aware of anything that would work?
 
If you have adequate water pressure to drive it, you can put two tank type water heaters in a row: Electric > Propane > Consumption.

The electric will preheat the water if it can (wire it to dump load), or if it's not there the propane heater will take care of it.

Some risk of Legionella to be considered though.

My propane water heater will be the last fuel appliance I replace. With the water district's backup diesel pumps and the pilot light propane water heater, I've never had a hot shower outage.

I was at a house once with a well pump and electric water heater, during an outage. That's a lot more dire outage situation than I'm used to. Like camping.
 
Last edited:
ericfx1984 said:
Anyone aware of anything that would work?
Click to expand...
plumb two water heaters in series. Use 6 valves so you can switch which is first. That way you don't have stagnant water in one tank when not in use.

Heat to 145 to avoid bacteria problems. Use a thermostatic mixing valve to blend down to safe 120 degrees.

Electric -> propane also works if you have excess in winter only. You have more heat being lost, but it is lost to the house, so no net loss.

If you only use electricity in winter to heat, then in my opinion, skip the heat pump. It takes heat from the house, which you have to replace with your house heater. Also resistance heating can dump energy faster into the water. If you might use in summer, then HPWH makes sense. HPWH also have a resistance element.
 
Last edited:
ericfx1984 said:
I have been thinking, propane is a great way to heat water... But if I have excess solar power, which happens a lot in the winter, I might want to heat with solar...

But I can't seem to find a water heater that can do this...

Anyone aware of anything that would work?
Click to expand...
I'd suggest to start by identifying how many extra kWh you have and how much hot water you need. This may not be something worth pursuing.

How much space heating do you need and how are you producing it? Rather than water heating you could look at supplementing space heating with common 1800 watt space heater when excess power was available.
 
ericfx1984 said:
I have been thinking, propane is a great way to heat water... But if I have excess solar power, which happens a lot in the winter, I might want to heat with solar...

But I can't seem to find a water heater that can do this...

Anyone aware of anything that would work?
Click to expand...
I just finished the plumbing on my hybrid heat pump water heater last night that is ahead of my propane water heater. It is a series setup. The heat pump water heater is wi fi connected which allows me to control whether I want to use the heat pump or 4500W electric element, timing on operation and temp.

If I used a heating element water heater, I would have had to install a control device to get similar control and there isn't any increase in efficiency like the heat pump.
 
For my purposes I bought a 30gal HW tank and replaced the 240vAC 4000w elements with 120vAC 2000w elements. Since only 1 element (top or bottom) runs at a time this puts the power need in line with my 3kW AIO to operate with excess PV production. Either grid or Inverter can feed the tank through a MTS and at the tank is a shut off switch for when not needed. Since on a sunny day (Fall -Winter) my batteries get topped off about noon I just go ahead and heat up the water . This changes the time for me to reach full battery till around 2pm. As Air conditioning season begins I will have to see if sufficient PV excess will still exist.

On average it takes about 2 hours from cold to heat the tank up to temperature shutoff. This than provides plenty of hot water for a shower and a load of laundry for myself.
 
hwy17 said:
My propane water heater will be the last fuel appliance I replace.
Click to expand...
Agree. With just two of us, we just don't use a huge amount of hot water. A shower each per day, a load in the dishwasher about 3x/week, and some laundry. The propane Rinnai tankless can go forever and a day, heating only when we use that hot H2O, and if for some reason we do need a lot of hot water, we never run out. Just no good reason to change, and a tiny amount of fossil fuel use.
 
Madcodger said:
The propane Rinnai tankless can go forever and a day, heating only when we use that hot H2O, and if for some reason we do need a lot of hot water, we never run out. Just no good reason to change, and a tiny amount of fossil fuel use.
Click to expand...
X3, Rinnai and Geothermal desuperheater here.
Rewired elements in series, so both thermostats require heat and lowers amperage draw on SolArk15k. When ever that's not enough, the tankless propane tops it off. 500gal of propane lasts us over 3yrs (including stove/oven and dryer), it's backup like a gasoline generator.

Water flows through both, so no stagnant water problems.
 
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hwy17 said:
Some risk of Legionella to be considered though.
Click to expand...
Which part of what you describe has a Legionella concern.. ( in heating hot water) As that was a thought of mine for excess solar first and then let it go to propane if needed…
Help ….I need another thing to worry about …..

J.
 
JRH said:
Which part of what you describe has a Legionella concern.. ( in heating hot water) As that was a thought of mine for excess solar first and then let it go to propane if needed…
Help ….I need another thing to worry about …..

J.
Click to expand...
Say if in the winter or shoulder seasons your dump load is only running a little bit, so the electric tank is staying warm and could harbor legionella. Then, normally it would go over to the propane tank and get killed by the heat but what if someone takes a long shower and the propane tank temp gets down, then you could have live legionella coming in, mixing in, and going out to the shower head.

I'm not sure there's ever been a documented case of residential legionella, so I'm not like a fear monger about it. But that would be the theoretical scenario.
 
hwy17 said:
Say if in the winter or shoulder seasons your dump load is only running a little bit, so the electric tank is staying warm and could harbor legionella. Then, normally it would go over to the propane tank and get killed by the heat but what if someone takes a long shower and the propane tank temp gets down, then you could have live legionella coming in, mixing in, and going out to the shower head.

I'm not sure there's ever been a documented case of residential legionella, so I'm not like a fear monger about it. But that would be the theoretical scenario.
Click to expand...
That is sorta consistent with what Im reading about on this topic with water storage tanks and moderate temps, but it’s abit confusing still… I never thought about water heaters …hmmm

I will dive deeper into it when im closer to doing it but that “legion” stuff is creepy in the way it’s somewhat elusive and random…( at least to me) ..

I am trying to incorporate more ways to utilize propane as an assistant to the solar gear for heat and other dual fuel back- up devices I own…and presently use everyday.

I have about 750 gallons of propane in several containers buried and on surface…aiming for 1000 gallons storage By next winter.
That’s a big part of my whole back up plan…if grid was unavailable ..

Thank you .J.
 
JRH said:
Which part of what you describe has a Legionella concern.. ( in heating hot water) As that was a thought of mine for excess solar first and then let it go to propane if needed…
Help ….I need another thing to worry about …..

J.
Click to expand...
Heat Geek goes over this, one thing needed is stagnant water.


If you are really concerned about Legionella then you can install a thermostatic mixing valve and heat water above 140°F. I would be more concerned using low temp emitters such as radiant floor that never was heated above 140°F. That is why one should occasionally bump the temp up before working on a system.
 
DIYrich said:
plumb two water heaters in series. Use 6 valves so you can switch which is first. That way you don't have stagnant water in one tank when not in use.

Heat to 145 to avoid bacteria problems. Use a thermostatic mixing valve to blend down to safe 120 degrees.

Electric -> propane also works if you have excess in winter only. You have more heat being lost, but it is lost to the house, so no net loss.

If you only use electricity in winter to heat, then in my opinion, skip the heat pump. It takes heat from the house, which you have to replace with your house heater. Also resistance heating can dump energy faster into the water. If you might use in summer, then HPWH makes sense. HPWH also have a resistance element.
Click to expand...
Bro what you mean by HPWH? High XXXXX water heater? Sorry for my ignorance some US terms no longer make sense to me being out of the country for so long.
 
Mattb4 said:
For my purposes I bought a 30gal HW tank and replaced the 240vAC 4000w elements with 120vAC 2000w elements. Since only 1 element (top or bottom) runs at a time this puts the power need in line with my 3kW AIO to operate with excess PV production. Either grid or Inverter can feed the tank through a MTS and at the tank is a shut off switch for when not needed. Since on a sunny day (Fall -Winter) my batteries get topped off about noon I just go ahead and heat up the water . This changes the time for me to reach full battery till around 2pm. As Air conditioning season begins I will have to see if sufficient PV excess will still exist.

On average it takes about 2 hours from cold to heat the tank up to temperature shutoff. This than provides plenty of hot water for a shower and a load of laundry for myself.
Click to expand...
TLDR: What is an MTS?

so i have waxed poetic about my dream of making a large scale water heater to heat house and of coure provide hotwater. I have since bought a 1700 liter insulated tank, and am looking at two of the heatpump water heaters to heat the tank up when the batteries are topped off, as well as a waste oil burner, water boiler for the coldest three months if needed. (mid December~Mid March) used heat pump water heaters are readilly available at a reasonable price (2~300 USD for a 6-12 year old unit)

I have also started acquiring parts fo the Waste oil burner water boiler as well. as such I am trying to gather as much info into my brain housing unit as possible. what is a MTS?
 
JRH said:
That is sorta consistent with what Im reading about on this topic with water storage tanks and moderate temps, but it’s abit confusing still… I never thought about water heaters …hmmm

I will dive deeper into it when im closer to doing it but that “legion” stuff is creepy in the way it’s somewhat elusive and random…( at least to me) ..

I am trying to incorporate more ways to utilize propane as an assistant to the solar gear for heat and other dual fuel back- up devices I own…and presently use everyday.

I have about 750 gallons of propane in several containers buried and on surface…aiming for 1000 gallons storage By next winter.
That’s a big part of my whole back up plan…if grid was unavailable ..

Thank you .J.
Click to expand...
rural indiana in the 70's was a 500 gallon tank minimum for a family of 4 and that was only if they would deliver in the winter...
 
Daddy Tanuki said:
Bro what you mean by HPWH? High XXXXX water heater? Sorry for my ignorance some US terms no longer make sense to me being out of the country for so long.
Click to expand...

Heat Pump Water Heater

Has a compressor/evaporator/condenser like an a/c system to heat the water along with a backup resistance element.

Usually called hybrid.

They name the room they are stationed in very cold.
 
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