# Solar Hot Water



## Rizzoni (Oct 3, 2008)

D anyone have experience with using a propane tankless hot water heater as backup for a primary solar DHW system? Is there a best model to look for, such as one with a low BTU kick-in to allow the tankless to minimally boost the solar water? Are electric tankless heaters better than gas for this purpose?


----------



## JeepHammer (Oct 10, 2008)

Rizzoni said:


> D anyone have experience with using a propane tankless hot water heater as backup for a primary solar DHW system? Is there a best model to look for, such as one with a low BTU kick-in to allow the tankless to minimally boost the solar water? Are electric tankless heaters better than gas for this purpose?


I didn't know they made a 'Tank-less Electric' hot water heater... Shows what I know.

I was using a timer on a gas hot water heater until it finally gave out...

Then I switched over to a Tankless Natural Gas hot water heater, and I couldn't be more pleased with it!

My gas bill is down about 60% (we still cook with gas) this summer.
We still heat with natural gas, so I'm sure I'll cry about the bill when it gets cold, but for now, I'm really impressed!
--------------------------------

Now, I'm not getting what you are saying for sure...
To get a solar heat panel to work directly, you would have to route the cold water source for the water heater up to your thermal collectors, then back in the house for the hot water heater supply.

That's not very practical for cold weather regions where the plain water would surely freeze at night an break the pipes in the thermal collector.

------------

The only way to do that in cold weather climates would be to use a heat exchanger tank just before the hot water heater, 
And circulate an 'Anti-Freeze' mixture up to the thermal collectors.
That would require a pump for the closed heat exchanger loop, and that is going to take power of one sort or another.

What we did one time 
(small scale for an experament more or less) 
was to run two fairly large 
(4'x8' total collection box area) 
home made thermal heat collectors and a closed loop with anti-freeze through them.

We ran the pump off a Solar PV panel (PV=Photo Voltaic, makes electricity) so when the sun came up, the boxes heated up and the pump came on automatically,
And when the sun went down, the pump shut off automatically...
No meddling from me.

the pump was powered by an old electric drill motor, and the PV panel was intended to charge batteries on seldom used vehicles so it wasn't expensive and worked fine for us.

The heat exchanger tank was an electric water heater tank that we installed heat exchanger coils in...
(Just copper tubing loops inside, through compression bulkhead fittings where the electric heating elements used to be.

The cold water supply went in and out through the fittings at the top of the tank like it would have normally.

We did fiberglass blanket wrap the crap out of it, and that actually helped quite a bit! I noticed the temp in the utility room when down right away when we wrapped that tank also (the gas heater had a heavy blanket already).

That rig just stored extra water in the house, and preheated the water for the the gas hot water heater so it didn't have to run as long.

I know that's not what you were looking for, but its as close as I can get with personal experience.


----------

