Thermal store or not?

[acorn]

I’ve spent weeks researching this and thought I’d made a decision but then someone threw a spanner in the works so hoping for some good advice on this forum!

I live in rural France and have NO heating source other than wood. At present I have a small woodburner in the kitchen and electric radiators in the other rooms we live in. The woodburner is alight from 7am-7pm throughout the winter so I thought it would be a good idea to distribute the heat produced to the rest of the house.

I have since bought a Villager AHI (14kw) integral boiler and have been contemplating the best way to plumb it in. I don’t necessarily need it for DHW as this is supplied by a mains pressure ‘chauffe-eau’. I do want it to heat approx 12 radiators throughout the house (total heat requirement approx 14kw). Relying on gravity-feed only isn’t an option as the pipe runs will have to run up-down-and back up again in some places.

I had resigned myself to a thermal store, but the only place for one would be where the ‘chauffe-eau’ is at the moment and size / weight restrictions limits me to a 300 litre thermal store. Because it would replace the ‘chauffe-eau’ means that the TS will need an electric element for heating DHW in the summer, or at a later stage I could add solar input into it. However the costs are mounting and I’m now looking at well over £2k for a 300 litre TS with electric element, solar coil, panels and Laddomat charging unit. I had thought the TS system would be great and would be sufficient to distribute the stored heat for quite a while before I would need to light the stove again but the answers I’m getting back at the moment suggest it would only distribute heat for approx 40mins – 1 hour before becoming cold. And of course if I’ve used that heat to warm the house up before I get out of bed it means there wouldn’t be any heat left in the tank to heat the DHW, so no shower first thing. I’d have to wait until the woodburner was relit and reheat the tank.

Do I really need to spend £2k or can I install something much more simple?

So now I’m re-thinking…keep it simple! Can I simply connect the woodburner to a pumped radiator circuit and if so, would a Laddomat still be an advantage to prevent cold water from entering the woodburner? I wouldn’t need DHW so there would be no tank / cylinder…just the radiators. Of course I will have to make way for 1 or 2 rads (without TRV’s) to be gravity fed in case of a power cut to act as heatsinks, but would I have to use all 4 tappings of the stove to do that or can it be incorporated at the start of the pumped CH circuit. I realise that the house won’t be warm and toasty first thing in the morning but the £2k I would spend on a TS would go a long way to pay for running a small electric rad in the bedroom for an hour before I get up!

My question then really is this…a simple but safe pumped CH system without DHW or gas/oil boiler back-up.

 

[peteheat]

Yes you can go simple but ensure the system is open vent instead of sealed / pressurised.

A 300 litre thermal store is really too small to be of any great help, we fit that size as standard hot water cylinders, one advantage is they can be used for solar, wood burner and an oil / gas boiler (three coils).

The thermal store really comes into its own when you have a large heat source and the store is 1,000 litres or more, it is possible to get as tank in tank type, the top used for hot water and the lower two thirds for central heating.

Laddomat might be a bit overkill, I would use an ESBE load valve 55c.

 

[unfinishedsweet]

Fit a buffer tank. Use biggest cylinder as you can fit, get simple direct hw cylinder commercial range with at leas 1" connections. Use tees on tappings to split primary and secondary circuit. Obviously open vent and you have the cheapest option. You need two pumps, one per circuit.

 

[acorn]

Yes you can go simple but ensure the system is open vent instead of sealed / pressurised.

A 300 litre thermal store is really too small to be of any great help, we fit that size as standard hot water cylinders, one advantage is they can be used for solar, wood burner and an oil / gas boiler (three coils).

The thermal store really comes into its own when you have a large heat source and the store is 1,000 litres or more, it is possible to get as tank in tank type, the top used for hot water and the lower two thirds for central heating.

Laddomat might be a bit overkill, I would use an ESBE load valve 55c.

Many thanks for that...here are my latest thoughts!

Anyway, the way I see it is that a Thermal store is really only beneficial if you have multiple heat sources - I DON'T.

I am very happy to continue using my 200 litre electric mains pressure water heater for my DHW, which cost less than 1 euro per night to heat up.

All I want is to distribute heat from the stove into some radiators.

So, bearing all that in mind why can't I simply use 2 diagonal tappings on the stove and plumb them directly into a radiator circuit? If that CAN be done then is it worth using a Laddomat (or similar) to prevent the cold return being too cold, already has a pump to circulate the heat and it will also allow self-circulation in the event of a power cut? Here is a sketch of the proposed radiator layout, but I'm not sure how the heatleak radiator should be plumbed in relation to the Laddomat or similar device.



A couple of things to note....
1) The heatleak rad is located in the opposite direction to the main CH radiators. Will that matter?
2) There will have to be 2 short (50cm) horizontal runs to the heatleak as the pipework has to run through stone walls.
3) The metal F & E tank cannot be sited directly above the stove but will be in fact 6metres horizontally from it but obviously at the highest point in the house. Schematics always show the F&E directly above the stove, but as long as it is within the primary pipework should that matter?
4) Should I use gradually decreasing pipe sizes the further I get from the heat source. e.g the furthest rads to have a 14mm run, working back to 16mm, 22mm and eventually the 28mm primary run to and from the stove?

Thank you in anticipation of helpful replies!!

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