Building a OWF on the cheap

[notshubby]

"I don't mind using a pump to circulate the water to heat the HWH I just didn't want the pump to run 24/7 like some of the systems I saw with plate X's. That seems like a waste."

a boiler guy told me a long time ago that he would have to replace pumps a lot more often when they were set up to turn on and off. and that a taco 007 which is probably the most common circulator pump out there only uses pennys worth of electricity a day.

 

[notshubby]

plus if you want to turn the dhw pump on and off you would need an aquastat or other temp sensing device installed at the hot water heater and run more wiring back down to the pump at the boiler.

 

[maple1]

A 007 at 0.7 amps (per specs) running 24 hours a day would amount to about 2kwh/day, or 60kwh/mo.

So at my rates that would be about $10/mo. Or $0.35/day.

So not a big amount.

 

[mcguyver1]

no think of it as the whole system is sealed boiler, heat exchanger, piping, except for the expansion tank which is wide open and at the highest point

Ok, now I get it. Where most unpressurized boilers have a pipe sticking out the top to monitor water levels and add water, your tank is sealed and you simply moved the pipe up to the highest point in your system.

I guess this would also help stop any air being trapped in your system. From what I understand, there is issues with air being trapped in the HX.

I'm curious, how many gallons of water does your system use and how much does that volume change in a ten degree swing in temp?

Can anyone tell if the pumps on the Freeheat4u website are any good?

 

[mcguyver1]

plus if you want to turn the dhw pump on and off you would need an aquastat or other temp sensing device installed at the hot water heater and run more wiring back down to the pump at the boiler.

notshubby. I have a propane powered HWH. I had planned on using a thermo-sensing device from a regular electric HWH. These are crude and simple, but reliable. They've been using them for years and don't require any electricity to operate. I have some nice (cheap) two conductor wire that I can run back to the boiler and activate a relay that would turn on the pump.

Maple1, You are right that it wouldn't break the bank running the pump all the time. By switching the pump on and off I would have better control over the actual temp of the water in the HWH rather than it just being the same as what ever the boiler is. I don't know if there is any truth to it but I read somewhere that if you heat the water to high it will cause more lime to drop out of the water than normal. Believe me, we already have more than enough lime issues. Does anyone know if there is any truth to this?

There is also the fact that the HWH is old and I don't know how 180F would effect it.

 

[maple1]

Ok, now I get it. Where most unpressurized boilers have a pipe sticking out the top to monitor water levels and add water, your tank is sealed and you simply moved the pipe up to the highest point in your system.

Except I don't think the tank is really sealed - or else it would pressurize the whole system as it warms up.

 

[maple1]

Maple1, You are right that it wouldn't break the bank running the pump all the time. By switching the pump on and off I would have better control over the actual temp of the water in the HWH rather than it just being the same as what ever the boiler is.

I don't think you would ever get it quite as hot as the boiler is, there are some efficiency & heat losses in piping & HX etc..

Also, with a sidearm setup, it is also possible to regulate the amount of heat going into the DHW by throttling the DHW side with a ball valve if the boiler side runs all the time. There would be some tweaking before you got it set 'right'.

 

[mcguyver1]

Except I don't think the tank is really sealed - or else it would pressurize the whole system as it warms up.

Maple1, you have my thinking. If the tank at the OWF had an open pipe in the top, wouldn't the water in his "atmospheric expansion tank" drain out since the boiler is much lower than the expansion tank and the top of the expansion tank is open?

Even though the "AET" is remote from the OWF tank, wouldn't it still provide pressure relief? I might be missing something. Let me know because I was actually planning on building my system that way,

 

[maple1]

Maple1, you have my thinking. If the tank at the OWF had an open pipe in the top, wouldn't the water in his "atmospheric expansion tank" drain out since the boiler is much lower than the expansion tank and the top of the expansion tank is open?

Even though the "AET" is remote from the OWF tank, wouldn't it still provide pressure relief? I might be missing something. Let me know because I was actually planning on building my system that way,

You would keep enough water in the boiler & tank that that wouldn't happen. So if you filled the system cold so that there were a few inches of water in expansion, it would never go lower than that. Except for evaporation losses. And when the system was fully up to temp, the tank would be big enough that it wouldn't overflow.