Steve Woodward

Agreed underfloor heating would make sense
Our place is already converted. Were I doing the conversion myself it would definitely be something I would consider. However retrofitting it would be costly. I wouldn’t want to interfere with the the seal against radon (a known risk with our geology). Building something on top would also be hard as the headroom downstairs is tight: 205 cm (6’ 8”). If I was converting this place myself I would build in passivhaus levels of insulation/ heat exchange and some sort of mason stove arrangements instead of a boiler.

Thanks for this. Brilliant feedback and more stuff to think about. Our plan in terms of valves and the like is to just use standard plumbing with compression joints. There would be powered as well as manual shut offs. Lots to chew over. I did consider using lime plaster as a sealant on the outside. Round here lime plaster, mixed with a bit of horsemuck and straw is the traditional way of finishing off walls that haven't been made of stone. This would mean the roof would need to hang over a fair distance so there isn't direct splashing on to it. In terms of temps this wouldn't be going any hotter than 70C. Given the thickness of the plastic I doubt this would cause significant deformation. The process here is as much about experimentation and learning to see whether this is feasible.

With pellet boilers our experience is that they can be a pig in a poke. There is no way you can find out how reliable the things are. The sales people will tell you any old guff, tell you they aren’t technical and besides the things are guaranteed.

It turns out you can take all of this with a pinch of salt. Whilst there is an accreditation scheme run by the MCS all this is about is showing that in lab conditions the boiler doesn’t produce too much co2. It says nothing about build quality or reliability. There is no objective verification and it seems that things are certified which aren’t worth anything. Many installing companies have gone bust as the subsidies petered out. Insurance backed guarantees cover you for a princely two years. Not much cop if your boiler gives out after three.

In our small village I know four people with biomass boilers. Three bought ones made by the same company in Sweden that made ours. None of us is happy. In our case we have been in the cold a number of times and last winter spent more on maintenance than fuel.

Pellet systems are temperamental. They don’t like dust, they don’t like humidity. How you are meant to keep things down to 20% humidity in Welsh mountains is beyond me. Virtually all our problems have been down to the fuel delivery system. I know how to strip the thing down, unblock it, get to restart and turn oxygen sensors on and off.. In short it has been a pain.

Solar PV, on the other hand, has been a delight. It works. It heats our water. Excess is delivered back to the national grid. OK we get nothing like what we pay for our electricity but it does at least work. Needless to say there is a massive variation during the year. In December we would be lucky to get 5 hours of sun (we are in a deep valley in mountains) on average 2 - 3kwh a day compared to 15 – 30 in June. (For context UK domestic hot water immersion heaters draw 3kw).

We have woodburning stoves. They heat up fast but lose heat almost as quickly once they are out. We are lucky to have our own wood. With three acres bounded by hedges (all overgrown hedges, and a main road which needs seemingly endless tree cutting to keep boisterous growth in check we don’t have to buy in. Having said that lumping the things around, dealing with brash let alone drying, chopping and splitting is a lot of work. Buying an electric hydraulic log splitter made a huge difference to the process. The beauty of these though is that they don’t need power to work. As long as there’s dry wood and the flue is clear, they work.

We are considering air source heat pumps and a thermal store. Hopefully our pellet boiler can limp on until the RHI payments run out (it's a 7 year scheme, we are now in year 4).

First off thanks for the input and the welcome.

William Bronson wrote:
So,  you would want these to be outside the building envelope?

Yes. The boiler is outside in a shed and the feed goes underground to the house. I would build these near the house.

William Bronson wrote:
Is your home at all insulated?

Yes. The walls are a mix of airbrick, rubble and faced with stone. It is slightly better than solid but still feels cold to the touch in winter.

William Bronson wrote:
Clearly it has lots of thermal mass,  but that may not be enough.
I wonder if glazing a wall could create a solar collector of sorts.

That would be nice but would be rather difficult given the planning regime where we are. We are in a national park and the planners like things to look traditional eg a barn needs to stay looking like a barn. My tendency is to not involve them unless it is absolutely necessary.

William Bronson wrote:
Would you run non-potable water  in a loop,  or would this be part of the potable water system?

Yes it is all indirect and completely separate from the drinking water not least because it would have inhibitor in to prevent limescale build up.

William Bronson wrote:
What ways are you planning on heating the water.
Storing enough PV as  heat to get thru an entire winter on seems unlikely, though it would be awesome.

Wouldn’t it just! ;-)

William Bronson wrote: I have no experience with straw bales,  but we do buy hay for our rabbits and the rodents love it.

The dogs keep down the rabbits but the mice and rats will get at everything given half a chance. I’d make sure it was all much proof.

William Bronson wrote: A south facing(?) wall of IBC's could have a solar  thermal collector on the face of it.

The main part of the house is all on the north side. Barns round here were designed to minimise solar gain.

William Bronson wrote: Bunching them together in a cube  would minimize surface area, heat loss and insulation expense.

Great minds think alike!

William Bronson wrote:Stack them along the wall of your home and they could shield that wall from cold air and summer sun, and the insulation would serve double duty.

Summer sun is rarely that unwelcome here, although with climate change local patterns here are as out of whack here as they are elsewhere.

William Bronson wrote:
Keeping the water thermally balanced might require a more elaborate plumbing scheme than just storing water.

We’ve planned for that and are working on an arrangement of valves including 3 way ones.

William Bronson wrote:
Consider that  an above ground pool type tank would require simpler plumbing,  have an even more minimal surface area than a cube, and offer a roof for solar.
Cost per gallon should be lower as well.

What we were thinking about was having 4 tanks (possibly more) where one is kept as close to 70c as possible so it could deliver a hefty amount of heat to the building when there is demand. The others would work as subsidiaries. We would have sensors (arduinos) towards the top and bottom of each to monitor the system temps. There would be remotely shuttoffable valves controlling the flow between them but with the facility to turn these off manually if the IT stops cooperating. I am working on this with a tame engineer who thinks along similar lines to me, is interesting in developing this as a pilot and making the design a publicly available resource. He definitely gets the message that critical success factors include reducing carbon, having a system which is bombproof and while smart it would have the option to manually control things. Currently our computer controlled boiler has decided it doesn’t want to talk to the net, can you imagine how frustrating this is when it doesn’t have any buttons to control it beyond a couple of on/ off switches?

In the meantime, I will definitely have a look at your link.

This is my first post. I have lurked here for a while and am calling this research rather than netbased prevarication!

We live in a large converted barn with solid stone walls a metre thick, double glazing and a thick insulated roof. The setting is rural but not excessively isolated.
The Welsh mountain climate is probably more like the Pacific North West: mild, damp and cool with warmish summers and generally mild winters. If it snows or we get frosts, generally minima are around -10 or -15/20C should the snow persist for a few days (rare, but not unknown).
We’ve mains power and water from a spring. We replaced the oil boiler. It was on its last legs and we don’t feel comfortable burning fossil fuels. Its replacement is a computerised biomass pellet boiler. This was an expensive, albeit subsidised, mistake. It is pointlessly complex, badly engineered and unreliable. This winter we spent more on repairs than fuel. It’s miserable being in a house where you can see your breath.
We have solar PV cells which are great. They divert spare power to heat our domestic hot water tank. This works fine from late March to early October. Building up a larger reservoir of heat for water based central heating in a thermal store would make sense. This would be heated by the boiler and the solar array.  It would also give us breathing room should the pellet boiler go off line.
We have woodburning stoves to provide back up heat, and I will install a rocket mass heater but this wouldn’t work in the side of the property that we rent out to holiday makers: in the UK they are still seen as niche and unlikely to pass local building regulations or insurance.
Commercial thermal stores are expensive. We are researching whether we could use stacked IBCs - intermediate bulk containers - as a practical DIY alternative. IBCs are sturdy, readily available and cheap. We would insulate these with straw bales. They’d sit on a wood framework on a hard standing with a damp proof membrane and clad with rough wood lapping (possibly even breathable lime plaster) and a roof to keep it all dry and pest free.

So here are my questions:
Has anyone got any hot tips on using straw bales as insulation? What sort of insulation do they give in the real world? Has anyone arrived at "U" or "R" values for them?
Are there any issues we should take into account using IBCs?
I’ve worked out that the house needs something like 26kw/ 89000btu to keep it snug.
Any thoughts on what sort of tonnage of water we should aim for?
Commercial boiler people are saying something around 2,000 to 2,500 litres of water. Given that another 2 IBCs would cost less than £100 delivered (+/- 130 USD) would we lose anything if we made this bigger? Space isn't an issue, we have land we can play with.

Sorry if this all sounds garbled, but I find the more I research and plan, the more questions I generate.
I am aiming for a system which is cheap, bomb proof and DIYable, avoiding C02 emissions and zero fancy tech just using with standard plumbing parts.

Any input or points to consider would be very welcome.