Water Storage OWB

[BRSS]

Is water storage recommended with outdoor units like the Greenwood Aspen 175? I seems to me that most people using water storage are using indoor/insulated shed boilers tarm, garn etc..
How do you size the water tank and where can I find dealers and information on prices?

 

[webbie]

As you will see by other discussions here, storage can be an advantage for just about any system. The 175 has a built in water capacity of 75 gallons, which is a nice little buffer, but certainly not enough to store heat for hours. So what is the proper storage amount? It depends....on a lot of things. Everything from the method of heat (radiant floor, baseboard, cast radiators, hot air) to the way that you intend to use the boiler. Some systems will work well without storage....using mixing valves and firing the boiler only in really cold weather.

There are a lot of suggestions here as regards storage ideas - search around the boiler room.

As to size, this depends on how long you want to be able to do without refueling the boiler and other such factors. It also depends on the temperature of the water that you need (at minimum) to make your heating system work. Systems designed for lower temp water will work better with storage since the temp of the storage can be drawn down further.

Back to basics - one pound of water raised or lowered 1 degree F is ONE BTU.
So 500 gallons of water weighs 4200 lbs or so. If you can raise that to 190F and then pull from it down to 140, that is a 50 degree difference. Multiply 50 x 4200 and we come up with about 210,000 BTUs of storage there.....plus the water in the boiler, weight of the steel, etc. - that would mean that the storage could provide 5+ hours of heat (40,000 BTU is enough to heat most homes in pretty cold weather) after the fire went completely out.

Rough calcs, of course.