Depends a bit on how auto is the chip-feed, presumably. If you wanted to operate it like a log batch boiler, burning hard and fast, then relying on the store till the next burn, then maybe 3000 ltr is not OTT. If an auger automatically feeds when temp drops, maybe significantly smaller is OK?

What Nick said, I don't know how responsive modern pellet boilers are to constant on/off demand but using it in that mode like a gas boiler may not be as fast as you would want therefore the batch burn and store route would obviously demand a buffer tank of some description, for e.g. DHW.

Without working out the numbers, if the pool is acting as the thermal store (which it can), there are evaporation losses to take into account. This will cause the temperature to drop, causing the heater to be called on, which will overheat the pool a bit. Then more thermal and evaporation losses.

Would it not be best to split the two systems, they have different heat demands, as does DHW and Space Heating.

Tom, do you know the heat loads that are needed for the pool and the office.

I suspect the 3000lt thermal store is more matched to the burner than the demand.

Work out your heat loads, then work from that.

That implies a heat load of 1.125 kW, split 60:40. Unless you mean kWh instead of kW a day, then it is 16 kWh a day for the house and 11 kWh for the pool. But that seems small to me.

Anybody else find this conversation weird on a number of levels?

First off, the original post asks about “our situation” without giving much clue as to the situation in question - general construction and size of house would be useful to know, for example. 130 kW boiler, even with a pool and offices, makes one think rather big and leaky, though.

Then Steamy pulls 1.125 kW out of somewhere. Where? All I can make match that is interpreting the 27 kW to keep the pool at temperature as 27 kWh/day then dividing by 24. But that's a) silly small (as he notes), b) ignoring the house and offices and c) not what TOM W said anyway (even where there's so much confusion, as between kW and kWh, it seems rude to re-interpret what somebody says without at a least querying it first).

Anyway, the volumetric heat capacity of water is a bit more than 1 kWh/(m³·K) - so taking 3 kWh out of a 3000 litre store will reduce its temperature by one kelvin (i.e., one degree Celsius). With heat loads of the order of 90 kW when the boiler is not running the temperature of the thermal store will be dropping at about 30 °C/hour or 1 °C every two minutes. Sounds like 3000 litres is pretty minimal to me if the circumstances really are as said.

Well I am very sorry to have troubled anyone. I was expecting the bit about kW but apart from that I'm none the wiser. Here was me thinking that growing our own timber to burn instead of oil was a good thing and that I would just ask for a bit of independent advice. Having built a house with double the insulation required and put up a turbine, I thought that after being a member on here for 4 years it was worth a go.

Tom W

I am also struggling to grasp the figures but again I have an old stone farmhouse on a 20KW system which replaced a 65KW oil fired system so insulation was a key element. Unfortunately there seems to be a breed of wood stove boiler salesman appearing whereby bigger is better especially in relation to RHI schemes even though they cannot be justified. No personal experience of Heizomat heaters but they do understand woodchip as I have a Heizohack chipper which consistently produces G30 spec chip unlike lesser quality chippers.