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Context - rural northern Scotland. Big old cold house - bit of a project. Currently on LPG and an old wood burning stove. And I'm comfortable (ethically/environmentally) that burning wood in my location makes sense.
I'm contemplating a new stove - and thinking about one with a back boiler. Long term thinking to keep the LPG for now but with the idea that that'll get replaced with air source heat pump in the future. And add PV or solar thermal panels. Idea would be to add/change the system without too much undoing of new additions.
The design of the house works well for a big wood store (quite open plan with the heat from a massive stove getting to the living areas and upstairs too. Add one with a back boiler to get a home office warm and into the bedrooms.
Anyone done similar?
Yes. Just wrote you an essay about it and pressed the wrong key and it is all gone. Sorry. 🙁
Basically it's a great idea and easy to implement if you are a bit handy with DIY plumbing.
Yes. I DIYed the entire thing and use old vented hot water tanks to make thermal store. Also DIYed the including control system. Went for simple relay logic as I ran out of enthusiasm for the control system and making up a nice daughter board for muC. Ours has a back up electric boiler that I can flip over by a few MOMO (i.e. not spring return) valves. You need to consider a heat link rad and a and several other passive ways of dumping heat that don't rely on power.
The main thing is that running a back boiler is work and is not for the brainless. You need to pay attention to it to run it well and safely. It is nice however when all the rads are hot and its all free heat (its never free even if you don't pay for the wood its still not free).
There are loads of ways of implementing this. You can link in pressurised systems (such as solar thermal or a pressurised lpg circuit) via loop in a thermal store or a plate heat exchanger.
Do you have any specific questions?
I have a thermal store like the one below except mine has solar input as well
https://www.coppercylinder.co.uk/open-vented-boiler-ovb-eco/
Old stone house with back boiler on the multi fuel stove.
It works well for us we are running the fire anyway as the major heat source.
I have the water heated by the immersion early in the morning although that is just a top up as the water is hot from the evening before. This allows the central heating to kick in before we get up. We then have the fire on during the day and it heats the water up again and the central heating kicks in later afternoon. If you have a good fire going you can put the radiators on again in the evening on really cold days.
We used to have night storage and I think the switch pretty much paid for itself in the first year.
we had a big boiler/stove log burner ( think about 25kw) when we moved into the current house. soon fitted an oil boiler and replaced it with a small log burner.
it wasn't plumbed in very well with the pump just being on a switch with no stat on it so may have worked better if done right but for our use was useless.
takes a lot of wood and from cold takes a long time to give much heat into the room due to have to heat the water as well. ours was lit coming home from work at 5/6 and only on for maybe 6 hours, when we were at home over one christmas and it had several days of being lit for 16 or so hours a day it did work much better but got through loads of wood.
was good for hot water though bujt at the time we had an electric shower so didn't actually use much of the hot water it generated.
not sure how well they integrate with other systems. our oil and log costs are now similar to what we were spending just on logs but we have a much warmer house.(adding insulation and new windows has also helped there)
Thanks all so far. From my googling there does seem to be a myriad of different design setups with ranges of success/efficiency.
Our LPG CH system currently has a TADO smart controller setup in every room - I can't see that working with a new setup. But it looks like a good challenge to sort it all out!
No reason the smart thermostat can't be involved. You may need to augment it to switch either automatically or manually between hear sources but it's only calling for heat so it would just be calling from the thermal store rather than the boiler when the thermal store is up to temp.
I had plans to make something smart but after sitting in front of a computer all day can't stand the Idea of doing so weekend and evening at the moment
cheers -
Also this
You need to consider a heat link rad and a and several other passive ways of dumping heat that don’t rely on power.
Is a very good point I hadn't thought of. We like a good power cut in these parts and it would be rubbish if you couldn't run the stove for fear of damage for lack of power for the pump.
You could have a bath but over heating is unlikely to be a big issue with a big tank
Thermal store + Boiler stove with a ladomat to control the flow to the store.
We had this setup + solar thermal in our last place which was off grid.
The store had inputs from Oil boiler, Multifuel boiler stove, solar thermal and a leccy immersion heater.
The ladomat deals uses thermostats to run what is a CH pump to take the heated water from the stove to the thermal store. You need to consider placing of the loops used for CH and water as you want to benefit from stratification in the store. The store also needs to be relatively near the stove. I retro fitted a cheap stat which fired the ch loop to dump the heat when tank got too hot. That was more an issue in the summer with the solar thermal though.
The CH side used a smart wifi controller. It was a good system, but it did scare the shot out of me the first time it boiled the loop from the stove to the thermal store.
https://mibec.co.uk/products/heating-components/laddomat/
You can deal with powercuts by using a UPS to power the stove to store and ch pumps - I never got around to fitting one though.
UPS is a good idea for the central heating pump as it is not high power.
We just have gravity heating our tank from the multi fuel stove, would a pump speed up the heat transfer?
EDIT: had a look at the link and it explains the benefits
You could have a bath but over heating is unlikely to be a big issue with a big tank
Yeah really it comes under my comment of "running a back boiler is work and is not for the brainless". There are requirements though within British standards.
P.S. Out link to thermal store is thermo sphon.
IIRC the there was a similar setup to the laddomat which managed the input from the solar thermal. The oil boiler was controlled using the hw control on the smart thermostat on/off with a target temp set. It was mainly used on shitty summer days when there wasn't enough sun to heat the store enough for the hot water needs.