The best kind is one that has a sealed combustion chamber and an external heat exchanger.
How to heat both my floor and sepate domestic water.
The idea here is to prevent domestic water from getting contaminated by stale water that sits uncirculated in the heating system during the off season.
The traditional boiler water may also be used for domestic hot water by directing the water through a separate integrated water heating unit before routing it to a fixture such as a faucet or shower.
As you can see this allows the boiler to heat a tank of potable water which in turn can provide domestic hot water and floor heating in an open or closed configuration.
In the summer water will stagnate for the floor heating and if it mixes with your regular water it won t be good.
Hot water from the boiler is circulated through radiators or a hydronic heating system to warm the ambient air.
The reason for this is to have the two water uses separate.
A dual purpose system relies on only one water heater to supply both the hot water requirements for the home and the warm water needed for the radiant floor heat.
Normally the wood boiler is plumbed to a heat exchanger see drawing above.
The same water that ends up in your hot shower or dishwasher for example has passed through the floor first.
Even if only part of the home uses.
One option is to keep domestic hot water completely separate from water that s part of the heating system using a heat exchanger.