A stove with a backboiler can be used to supplement your existing heating system or to entirely run your heating and hot water. When we specify a large boiler stove we like to ascertain the heat demand of your house first so that we can be sure that the stove has the required heat output.
As a rough rule of thumb domestic hot water generally takes 2.3-3kWh/person /day (8-10,000 BTU), whilst an average radiator (3′ x 4′) takes around 1.5kW (5,000 BTU). This rule of thumb is no substitute for the advice of a good plumber / heating engineer. You can use our BTU to kW converter if you want to convert BTU to kW or kW to BTU, however please be warned that just adding up the outputs of all the radiators in your house will usually give you a total figure which is too high and so it is not a good basis for sizing your boiler stove.
Wood fired central heating > Thermal Stores
Put simply a thermal store tank is a large, well insulated, hot water tank, and forms the heart of your home heating and hot water system. A thermal store (or buffer tank) as the name suggests, stores up heat. Thermal stores are used extensively in solar systems where the heat from solar panels is stored in the large body of water, which then provides you with hot water during the times when the sun is not out.
You can also heat your house using heat stored in the thermal store. You might run radiators or perhaps underfloor heating from your tank: underfloor heating is ideal for use with thermal stores because of the low loop temperatures. This means that you can have the heating come on even if your log boiler is not lit.
The thermal store also lets you link up different heating systems, most notably it lets you link in a stove with a backboiler. A woodburning stove with a backboiler is the perfect companion for solar thermal panels because in summer when you wouldn’t dream of lighting your stove the panels provide your hot water and you don’t need the heating. In the winter the stove is lit and providing hot water and heating, and the solar panel is contributing a little by raising the temperature of the water at the bottom of the tank (to around 30-40 degrees or so in my tank ) – every little helps.
You can of course plug in just about anything else to the the thermal store: another stove, a wood pellet boiler, a conventional boiler for backup, electric heating elements (again as a backup source of heat), ground or airsource heat pumps, etc. The thermal store is the central point in your heating and hot water system – all your heat sources connect to it and all your heating is taken from it.
One of the big tricks of thermal store is to improve and maintain good stratification (just follow the link in to find out what this is all about). Put very simply the idea is to keep the water at the top of the tank hot, and the water at the bottom of the tank cool, with as little mixing as possible between the two layers.
A wood stove will work best when burning quite hard – wood likes a good supply of air to the firebox. But burning your stove hard can mean your house getting too hot. The other advantage of using a thermal store in conjunction with a relatively large boiler stove is that it lets you batch burn: you fill up the stove and burn it relatively hard and it heats up (or charges) the thermal store. You now have hot water which you can use as needed. Of course this can also let you use a larger stove than you might have before which lets you use longer logs (less time spent processing and moving your wood) and lets you burn the stove less often.
Thermal store are of course ideal for use with log gasification boilers – these are high output, semi-automatic log boilers which would normally live in an outbuilding. They have very large fireboxes and so you load and fire them up a lot less than a traditional boiler stove, which means more time putting your feet up, but they must be matched with an appropriately sized thermal store.