I have been told that using a wood-fired boiler to provide hot water to
an underfloor (radiant) heating system requires the use of a v. large
storage tank to act as a buffer for supply temperatures. Is this true?
Here is the background to my question. We are reviewing our plans for
the planned heating system for a very old farmhouse we are renovating.
It's near the French Alps, we're at about 650 m (2000 feet) above
Current plans are for a gas-fired combination boiler (about 25 kW) to
provide hot water for domestic use and for radiators in the downstairs
rooms, about 110 sq. m. or roughly 1200 sq.ft.
Next year, we plan to renovate the remainder of the house. The large
upstairs areas (former hayloft) are supposed to get underfloor heating
coils, so the demand for hot water will increase greatly, albeit at a
We had hoped to meet this need with a wood-fired boiler, while
retaining the gas unit for emergency or back-up use in the future. It
would also provide domestic hot water during the warmer months, when
the wood unit is shut down.
Now our heating installer tells us that, due to the unstable output
temperature of wood-fired boilers, we are going to need a huge buffer
tank (about 2000-3000L, or over 500 gallons) so that the temperature of
the water going to the floor heating coils is reasonably stable.
We haven't chosen our wood unit yet, don't even know if it will use
pellets or logs. What we want to do is install our Phase I system
rapidly and cheaply, keeping our options open for the choice of our
future wood unit in Phase II.
An excellent climate for solar house heating, which would be on-topic for
alt.solar.thermal. Grenoble has about the same weather as Phila in January.
You might also look into a metal roof from