Combination solar / gas water heater

[Brian53713]

I'm wondering if combinations solar-heated water /gas as a backup water heaters are very common? I already have a solar space heater, as a place to possibly attach the water heating Contraption over the top of? My researching it only came up with tankless water heaters.

[Mike90250]

I use a rooftop solar water heater, which preheats water for my tankless water heater. Reduces propane usage a lot. I can't imagine why it would not work for a tank style heater either, unless you feed it water that is too hot and trips the safeties .

[J.P.M.]

If your fossil fuel source is natural gas, chances are it will not be cost effective to use solar energy to provide domestic hot water. Therefore the combination of solar water heating and gas is unusual at this time.

[Brian53713]

My water heater is natural gas, and older. Is a normal natural gas water heater still the best replacement option ? 5 people utilizing, use spread out. We get by with a low heat setting.

[inetdog]

I use a rooftop solar water heater, which preheats water for my tankless water heater. Reduces propane usage a lot. I can't imagine why it would not work for a tank style heater either, unless you feed it water that is too hot and trips the safeties .

In many cases there will be more problems with a tankless "booster" than with a tank type booster, even when the preheat tank is cooler than the target temperature for the hot water.
The biggest potential problem is that for low or moderate flow rates the tankless gas heater may not be able to throttle its flame down enough to keep the outlet temperature below the set point.
Either the tankless will shut down completely or it will cycle on and off instead of modulating the flame.

[Mike90250]

In many cases there will be more problems with a tankless "booster" than with a tank type booster, even when the preheat tank is cooler than the target temperature for the hot water.
The biggest potential problem is that for low or moderate flow rates the tankless gas heater may not be able to throttle its flame down enough to keep the outlet temperature below the set point.
Either the tankless will shut down completely or it will cycle on and off instead of modulating the flame.

That's why my tankless booster has 3 burner settings, and a tempering inlet valve set for 120F input
Google "caleffi thermostatic mixing valve #521"

[inetdog]

That's why my tankless booster has 3 burner settings, and a tempering inlet valve set for 120F input
Google "caleffi thermostatic mixing valve #521"

That is where we differ in setup. I run my tankless at 120F output most of the time, so I do not have nearly as much headroom for the tankless to operate.
A tempering valve on the output, OTOH, would not help at all with a tankless because you would still end up with an even lower flow rate through the tankless for a given delivery end flow.
In some cases a small averaging tank on the output of the tankless might do the job.

[Mike90250]

Tempering valve is on the input. so I never exceed the thermostat setting. And the Eternal model has a large volume condenser, holds about 2 gallons so there is no sandwich or delay. I've also got a recirc pump, to have instant hot at the faucets, water is more valuable than propane.

[J.P.M.]

Tempering valve is on the input. so I never exceed the thermostat setting. And the Eternal model has a large volume condenser, holds about 2 gallons so there is no sandwich or delay. I've also got a recirc pump, to have instant hot at the faucets, water is more valuable than propane.

Do you have a timer on the recirc. pump ?

[Mike90250]

Yes, there is a timer, at night, it only runs 5 min per hr

[J.P.M.]

Yes, there is a timer, at night, it only runs 5 min per hr

Thank you.