Log burner thermal store sense check
Discussion
We live in an 1850s farmhouse in NE Scotland so our heating bills are a bit steep.
I’d like to fit a log burner (have access to cheap/free wood) when we do a kitchen extension and plumb it into a water cylinder to use as a heat store. Our main heating system is unvented so we’d need a vented system for the log burner.
I’d like to fit temperature controlled valves to isolate the thermal store if the fire isn’t on so we’re not heating it with the boiler.
Anyone see any downsides or things we should consider for this idea?
I’d like to fit a log burner (have access to cheap/free wood) when we do a kitchen extension and plumb it into a water cylinder to use as a heat store. Our main heating system is unvented so we’d need a vented system for the log burner.
I’d like to fit temperature controlled valves to isolate the thermal store if the fire isn’t on so we’re not heating it with the boiler.
Anyone see any downsides or things we should consider for this idea?
I am not an expert here, but I think you should take a look at low loss headers. As I understand it, this is the normal way to connect multiple heat sources to one system. I think that due to the way the flows work, you shouldn't need the valves - as long as each source is separately pumped.
biggiles said:
I'm also not an expert, but I would be very cautious putting any kind of valve in the circuit with a log-burner's back boiler. Too much to go wrong, even if you have various expansion/safety valves.
The "low loss headers" sound like a viable alternative.
The valve would be to isolate the thermal store from the house central heating. The actual log burner to store loop would be unaffected. The "low loss headers" sound like a viable alternative.
The low loss headers appear to allow different heat sources to work on the same system but our heating is a sealed system and the log burner system has to be vented. Hence using a thermal store to transfer heat from the log burner into the system for the house without any actual mixing.
I have a 500 litre thermal store heated by a back boiler in a woodburner, oil boiler and immersion heaters.
The oil boiler and woodburner have their own pumps, no valves. There is temperature cut out to turn the boiler off if the tanks too hot, and a thermoswitch to put the UFH pumps on if the woodburner is overheating the tank.
First two years I just had the woodburner but it struggled when very cold and was impossible when we went on holiday in the winter.
I just have the upper immersion permanently on so that my two daughters can always have a hot shower. Beware that if you have a bespoke system, no hot water is always your fault!
The heat stratification is unbelievable, I can get a 50 deg difference from the top of the tank to the bottom.
The oil boiler and woodburner have their own pumps, no valves. There is temperature cut out to turn the boiler off if the tanks too hot, and a thermoswitch to put the UFH pumps on if the woodburner is overheating the tank.
First two years I just had the woodburner but it struggled when very cold and was impossible when we went on holiday in the winter.
I just have the upper immersion permanently on so that my two daughters can always have a hot shower. Beware that if you have a bespoke system, no hot water is always your fault!
The heat stratification is unbelievable, I can get a 50 deg difference from the top of the tank to the bottom.
Hello from NE Scotland!
In the event of a powercut will the valves go to your desired location, so you can warm the house? - or indeed warm a tank of water for a hot bath? - manual valves?
If you are thinking about a thermal store - I used to recommend a walk around the stove shop in Alford, he had a really nice wood stove that had a thick granite (or marble) covering, the idea being it took a long time to warm up, but once warm it stayed warm for a long time.
(I might have heard he has sold and moved on, but that might be incorrect, my dealings were brilliant)
In the event of a powercut will the valves go to your desired location, so you can warm the house? - or indeed warm a tank of water for a hot bath? - manual valves?
If you are thinking about a thermal store - I used to recommend a walk around the stove shop in Alford, he had a really nice wood stove that had a thick granite (or marble) covering, the idea being it took a long time to warm up, but once warm it stayed warm for a long time.
(I might have heard he has sold and moved on, but that might be incorrect, my dealings were brilliant)
Peanut Gallery said:
Hello from NE Scotland!
In the event of a powercut will the valves go to your desired location, so you can warm the house? - or indeed warm a tank of water for a hot bath? - manual valves?
If you are thinking about a thermal store - I used to recommend a walk around the stove shop in Alford, he had a really nice wood stove that had a thick granite (or marble) covering, the idea being it took a long time to warm up, but once warm it stayed warm for a long time.
(I might have heard he has sold and moved on, but that might be incorrect, my dealings were brilliant)
It’s more for heating a tank that the central heating takes heat from when the fires been on all day. Thus reducing our oil bill. Essentially topping up the heat in the system rather than completely replacing the oil boiler. For hot water we’d just use oil as it doesn’t use much anyway. In the event of a powercut will the valves go to your desired location, so you can warm the house? - or indeed warm a tank of water for a hot bath? - manual valves?
If you are thinking about a thermal store - I used to recommend a walk around the stove shop in Alford, he had a really nice wood stove that had a thick granite (or marble) covering, the idea being it took a long time to warm up, but once warm it stayed warm for a long time.
(I might have heard he has sold and moved on, but that might be incorrect, my dealings were brilliant)
The log burner will be in s kitchen extension, so not an ideal location for heating the rest of the house up.
In hindsight we should have replaced the open fire in the living room with a log burner but didn’t expect to be using it as much or want to dig a big hole in the wall for clearance.
When I moved into my place they essentially had two separate systems
One was a conventional oil boiler heating system to every room
The other was a wood burner with back boiler which feed an entirely separate and partial - heating system
The idea being that the oil system would pick up the slack and do early mornings etc whilst the log burner kept the core rooms warm whenever the fire was on
I removed when I renovated as heating oil was 40p at the time - regretting it now
One was a conventional oil boiler heating system to every room
The other was a wood burner with back boiler which feed an entirely separate and partial - heating system
The idea being that the oil system would pick up the slack and do early mornings etc whilst the log burner kept the core rooms warm whenever the fire was on
I removed when I renovated as heating oil was 40p at the time - regretting it now
Speed addicted said:
We live in an 1850s farmhouse in NE Scotland so our heating bills are a bit steep.
I’d like to fit a log burner (have access to cheap/free wood) when we do a kitchen extension and plumb it into a water cylinder to use as a heat store. Our main heating system is unvented so we’d need a vented system for the log burner.
I’d like to fit temperature controlled valves to isolate the thermal store if the fire isn’t on so we’re not heating it with the boiler.
Anyone see any downsides or things we should consider for this idea?
If you want to close off the oil boiler to the store it’s easy - just fit a valve operated by the boiler timer with a cylinder stat in series with it to either fill the store if cold and timer is on, or not.I’d like to fit a log burner (have access to cheap/free wood) when we do a kitchen extension and plumb it into a water cylinder to use as a heat store. Our main heating system is unvented so we’d need a vented system for the log burner.
I’d like to fit temperature controlled valves to isolate the thermal store if the fire isn’t on so we’re not heating it with the boiler.
Anyone see any downsides or things we should consider for this idea?
Rather than a hot water cylinder with two coils (one coil traditionally vented with metal header tank etc gravity fed for wood, and a second coil that’s sort of unvented for the oil boiler) you could do a proper thermal store. It’s possible to go unvented but you do need the right bits - we have an unvented log burner feeding an unvented store I turn supplying unvented radiators - the boiler stove is pressure rated, has a 2 or 3 bar blow off valve and also a quench coil in the jacket that will allow mains pressure cold water through a cooling coil in the jacket if the boiler goes over temp. In theory it’ll never explode. Very common in Europe. A laddomat 21 charging pump works off a flue and/or boiler jacket stat to pump the heat into the store via a coil low down in the store, aiming to fill the store as much as possible with free wood energy while not overcooling the stove and causing tarring. The store also has a direct fed gas boiler and a second upper coil for solar thermal and summer hot water. It’s been working every winter for probably 15 years.
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