Using Log Burner for heating water

[wcavanagh]

Interesting, doing a complete renovation to a 1900 cottage, this includes UFH thoughout.

The wife would like to have a log burner with hot water heating feature included in this design.

From what I can gather that part of the system needs to be open vented with header tank, as it is an uncontrollable heat source, can someone confirm this for me, 100% this is the only way?

Reason I ask is we have open ceiling in that area and no space directly above for this tank, but I can build an outbuilding directly behind to house this.

Just need to know this is how it works, as plans are going in for building warrant, etc.

By the way I would use this outbuilding as boiler room anyway.

Cheers All

 

[wcavanagh]

Someone mentioned sealed wood burning stoves are available now also.

 

[Jackrae]

Considering you cannot control the loss of electrical power (for pumps or valves etc) I would surmise that any solid fuel water heating system must be gravity circulated with "free" expansion capability.
I have a Clearview 500 fitted with a stainess steel back boiler which is capable of providing DHW service to the house. This is connected via gravity circulation pipework directly into my DHW open vented storage tank.
I would however point out that the relatively cold boiler surface does reduce the radiated heat output of the stove since there is no "back" ceramic reflecting heat back into the fire.

 

[Agile]

All uncontrolled appliances must be connected to a source of water so that in the worst case the can boil off the water and thus prevent the temperature from exceeding 100 C.

But I urge you to take care with the UFH. Once installed the heat output cannot be increased.

You need to work out the heat loss and ensure the UFH output will be sufficient. With four solid walls that will be quite high unless you are fitting proper wall insulation.

Because the UFH installation cost is very high then I would want to over size it by perhaps 20% as a precaution.

Tony

 

[bernardgreen]

I would surmise that any solid fuel water heating system must be gravity circulated with "free" expansion capability.

That is correct.

And as Agile mentions there has to be a reliable source of cold water that can be boiled off into stean by an "out of control" system. Ideally the cold water source would be a storage tank with enough water to cope with a full load of fuel in the stove. ( mains water could fail if there is a power cut to the area, unlikely but not impossible if the mains water is boosted by a pump serving the area ).

If (when) the boiler over heats then steam and boiling water will be coming out of the expansion pipe. It may be wise to vent this pipe outside the building rather than pointing the end down towards the cold water tank and risking a loft / attic full of steam.

 

[wcavanagh]

Thank you for the info very interesting.

saw this

http://www.broseleyfires.com/Technology.html

 

[wcavanagh]

I should add primary heat will be supplied by oil boiler, this was just a secondary source, plus we sometimes have access to lots of free wood, so would like to make best use of this. Was thinking a twin coil cylinder, heated by boiler and / or log burner.

 

[Agile]

A twin coil cylinder could be used.

They are more often sold as a cylinder for solar heating.

Ideally unless the stove circuit is pumped then the heating coil for gravity circulation should be 28 mm rather than the usual 22 mm. But pumping the stove output could be a good idea as with a cylinder stat turning the pump off can be used as a basic temperature control.

But be aware unless you add temperature controls to the stove heating coil then the stored water could easily exceed the recommended maximum of 60 C and create a risk of scalding.

 

[wcavanagh]

Yes I would have things controlled etc. Think next step is to contact come plumbers and see what they say. Thanks guys.

 

[bernardgreen]

But be aware unless you add temperature controls to the stove heating coil then the stored water could easily exceed the recommended maximum of 60 C

Yes I would have things controlled etc

With solid fuel such as a log burner there has to be a way to reduce the rate of burning of the fuel if the water system cannot absorb any more heat. This is normally achieved by shutting off the air supply to the burning fuel by means of a manually operated damper that closes the air inlet. If a stove can be used to heat water when no one is present to close the damper then this damper should have a fail safe mechanism that closes it when the water is approaching the maximum safe temperature.

 

[Roger928]

But I urge you to take care with the UFH. Once installed the heat output cannot be increased.

Tony

Raising the flow temperature increases the output.
If you fit a good compensator with intelligence it will do that automatically.

 

[Roger928]

A fan assisted log boiler will shut down the fan and air inlet according to the pre set values programmed into the on board controller upon commissioning. You don't need hydronic heat sinks for them when a power failure occurs.

If the log boiler has no internal cooling coil then it will need to go on a vented circuit.

 

[Agile]

Raising the flow temperature increases the output.

If you fit a good compensator with intelligence it will do that automatically.

Yes, but the flow temp is usually limited by the flooring cover or just the discomfort of having a floor too hot to stand on!

 

[bernardgreen]

A fan assisted log boiler will shut down the fan and air inlet according to the pre set values programmed into the on board controller upon commissioning.

Not all log burning boilers are fan blown. They will continue to take in air if the air inlet isn't closed. If the air inlet damper is motorised then with a power cut the damper cannot be motored to closed unless there is a back up battery to supply power to close the damper

 

[Jackrae]

As I read it, the OPs query suggested he was installing a log stove, not a log boiler.
But he still needs to consider loss of electrical power and, I'd suggest, loss of mains pressure.