one for the plumbers?

[Tim Lamb]

Heading into the home heating season, I am giving consideration to installing a log burner. The existing fire opening and flue are adequately sized for something up to 12kW and I think a flexible liner should be easy to install. There is enough dead standing timber on the farm to see me out, so security of supply is not a major issue.

However, although this is an open plan house including open stair well, the most convenient location is in a room only 14' x 14'. I guess anything over 6kW in such a small space will seriously overcook us.

Conversely, the ability to draw off useful hot water seems limited to 1 or 2 kW at most.

At the risk of awakening Drivel, how would one incorporate such an intermittent source of heat into a gas fired fully pumped system? The existing hot water cylinder, pump and controls are conveniently directly above the preferred location: assuming the joists are adequate!

regards

[The Natural Philosopher]

Open the doors Tim. It will at the least heat the room above, and some adjacent ones, leading to a general reduction in CGH bills, and a woodburner can be throttled way back, especially with good dried wood as fuel.

That is enough to fully heat a large insulated house for 3/4 of the year.

You probably need some sort of secondary pump and seection of morosed valves that will circulate that hot water thruogh all primaries instead of te boiler. I.e. some form of changeover switch so that when there is enough heat being produced by the fire, it takes over as a 'boiler'

An alternative approach would be to run the CH/DHW return through the woodburner to 'preheat' the water ..that would work very well indeed, except that when the burner is on, and there is no call for heat I can foresee the ruddy thing boiling. ISTR the usual approach here is a gravity fed towel rail or whatever in the woodburner circuit.

MM. I think the latter approach offers the best way..just need a way of dumping heat out of the burner backboiler when no call for heat exists. Maybe you could couple in some kind of thermostat to turn the pump on and the CH on whenever the boiler reaches critical temps. And use the house CH as a heat dump. Simply wire that lot in parallel with your normal timer and main stat..

Interestingly, this approach means the stove itself when not lit becomes a rather cute radiator..

[dom]

You might find the Rayburn tech page on plumbing in solid fuel stoves useful:

[Dave Liquorice]

No a solid fuel boiler must be able to dump it's heat without any power(*). ie an open (as in no valves, other than isolating ones for maintenance) gravity loop. You interface this to the existing system with a "dunsley neutraliser".

It would be wise to have a radiator (more than a towel radiator as well) on the wood burners gravity loop as a place to dump heat when the HW cylinder is boiling (literally). This can be controlled with a thermosatic valve, that is one with a wax sensor on the pipework which opens the valve when it gets to hot.

(*) Partly so you don't run the risk of having a valve fail closed or a power cut when you are not around with the fire burning and the thing exploding or generating rather more hot water, steam and pressure than one would like. And, probably more important so that you don't have to shut down your independant source of heat when there is a power cut.

[robgraham]

a miniature heat bank. The alternative is to go the heatbank route and run the wood burner into a second coil. You most certainly, as DL says, must run the wood burner in a gravity feed manner. You'll find the DN's via Google.

My system runs both DHW and CH through the neutraliser so that the wood burner can support the CH when it is running well. I've a differential thermostat of home design to switch off the CH boiler while the wood stove is hot enough to run the CH. It may be that with the low HW output you have that the Neutraliser should be on the DHW path only.

Rob

[The Natural Philosopher]

Not neceesarily. The woodburner here had a gravity rad as emergency heat dump, bur was coupled into the pumped storage in normal operation.

I never figured it ourt completely though, and removed it all when the house got demolished.

Perhaps that is teh answer: a gravity loop when a 2-way motorised valve is 'off' and then simply in series with the boiler when 'call for heat' is on.