Hot water storage?

[Bone1099]

Im new to the boiler room so please dont ridicule me too badly.
How much hot water stored and insulated from cool weather would be required to (supplement)heat 2 small bedrooms overnight.
Is it feasible to heat the water during the day with a solar heater and store it well insulated to supplement these two bedrooms overnight. My woodstove in the other end of the house keeps things pretty comfy but these two bedrooms get a bit cold on single digit nights. suggestions appreciated ridicule accepted.

 

[jebatty]

I would love to answer your questions, as I am sure many others would, but you are asking a question kind of like "how many miles per gallon gas does a motor vehicle get?" A diesel semi might get 4 mpg, and one of the better hybrid autos might get 50+ mpg. You need to provide lots more info to even begin to answer your questions.

 

[Nofossil]

The amount of storage that you need depends on the heat loss from the portion of the house that you're heating, the maximum temperature that you can readily achieve in your storage, and the minimum storage temperature that provides enough heat to be useful.

Heat loss can be calculated - search for Slantfin on this forum. They have a spreadsheet that you could use. In your case, just for the rooms that you want to heat.

The maximum temperature that you can reach in storage will depend on the sun angle, sun intensity, length of day, and solar panel performance. In Vermont in the summer, I get a peak temperature of about 175°F from my panels, and I get an average output temp of around 160°F. On a really good day I get about 100,000 BTU from them. However, I get 100,000 BTU when I'm heating water that's around 110°F. If I were heating water that was already 140°F, I wouldn't get as much heat energy from the panels (though my outlet temps would be a bit higher).

Here's where it gets difficult. My house has hot water baseboards, and they're not much use with water temps lower than 140°F. If I started with a storage tanks at 160°F, I would be pretty much done when it reached 140°F.

Here's the calculation: required storage in gallons = required BTUs / (8.3 * (max temp - min temp))

Let's say that you need 50,000 BTU and you maximum storage temp is 160, and your minimum is 140.

required storage = 50,000 / (8.3 * (160-140)) = 301 gallons

You'll of course need to plug in your own numbers. Radiant floor heating can use lower temperature water. That improves solar panel performance and allows smaller storage.