Stoves with a back boiler: how they work and what to check
A boiler stove, often called a stove with a back boiler, heats the room it sits in and also heats water for a hot water cylinder and, on larger models, a set of radiators. They have long been popular in rural Ireland. They also need more careful planning than an ordinary room stove.
How a back boiler works
Inside the stove, behind or around the firebox, is a water jacket: the boiler. Water from the heating system passes through it, picks up heat from the fire and carries it away to a cylinder or radiators. The rest of the heat warms the room directly through the stove body and glass.
Manufacturers usually quote two figures, for example a nominal output to water and a nominal output to the room. Those two figures matter more than the headline total, because they tell you whether the stove can realistically run the number of radiators you have in mind while keeping the room it sits in comfortable rather than overheated.
Types of system a boiler stove can connect to
A solid fuel fire cannot be switched off instantly the way a gas or oil burner can. Even with the air controls closed, the fire keeps producing heat for some time. The heating system has to be able to cope with that heat safely. Common arrangements include:
- Open-vented systems with a feed and expansion tank and an open vent, and usually a gravity circuit to the cylinder plus a "heat leak" radiator that can always take heat away, even during a power cut when pumps stop.
- Linking to an existing oil or gas system through a neutraliser, link-up unit or plate heat exchanger, which lets the stove and the boiler work together.
- Thermal stores or buffer tanks, large insulated cylinders that soak up heat from the stove and release it to radiators and hot water as needed.
Some boiler stoves are approved for use on sealed (pressurised) systems with specific safety devices; many are not. The stove manufacturer's instructions are the deciding document, and the design should be done by an installer experienced with solid fuel heating systems.
Safety essentials
- Never light a boiler stove that is not connected to water. A dry boiler can be damaged quickly, and a boiler that is isolated from the system can build pressure dangerously.
- Keep the heat leak open. Valves should not be fitted in a way that allows the stove to be shut off from its safety circuit.
- Plan for power cuts. If the system depends on a pump, there must be a route for heat to escape when the pump stops, typically by gravity.
- Carbon monoxide alarm. Under the Building Regulations Technical Guidance Document J, a carbon monoxide alarm should be provided when a new or replacement solid fuel appliance is installed in a dwelling.
- Chimney and flue. The flue must suit the appliance and be swept regularly; see our chimney sweeping guide.
Sizing a boiler stove
Undersized stoves get over-fired in an attempt to heat too many radiators. Oversized stoves overheat the room and are run slumbering with the air shut down, which is smoky and tars the flue. A sensible approach is to:
- Work out the heat needed for the room the stove sits in.
- Add up the outputs of the radiators the stove is expected to serve, plus the hot water cylinder.
- Choose a model whose output to room and output to water match those two numbers as closely as possible.
A home's insulation level matters a great deal here. The SEAI Building Energy Rating (BER) assessment is a useful starting point for understanding how much heat a house actually needs.
Fuel and Ecodesign
Boiler stoves are covered by the same EU Ecodesign rules as room stoves (see our Ecodesign stoves guide), and they must burn fuels that are legal to sell under the Irish solid fuel regulations. Multi-fuel models can burn approved smokeless fuels as well as wood; wood-only models are designed for logs. Dry wood is essential: wet wood in a boiler stove deposits tar on the boiler surfaces as well as in the flue, cutting heat transfer.
Running costs and expectations
A boiler stove can make good use of wood a household already has access to, and keeps a sitting room warm while topping up hot water. It is, however, a hands-on way to heat a house: someone has to light it, refuel it and clean it. It does not hold heat overnight the way a storage system does, and output varies with how it is fuelled. Many households use a boiler stove alongside another heat source rather than on its own.
Grants are a common question. SEAI does not currently offer an individual home energy grant for solid fuel stoves, including boiler stoves; see home heating grants and stoves.
Archived boiler stove and range models from the old showroom are listed in the stoves catalogue archive and cookers archive (historical information only).
Frequently asked questions
Can a stove with a back boiler run radiators?
Yes, if the stove's output to water is large enough for the radiators and hot water cylinder it serves, and the system is designed for solid fuel with a safe route for excess heat.
Can a boiler stove go on a sealed heating system?
Only if the manufacturer approves it for sealed systems and the required safety devices are fitted. Many boiler stoves are designed for open-vented systems or for connection through a heat exchanger or thermal store.
Is a carbon monoxide alarm required with a boiler stove?
Technical Guidance Document J of the Building Regulations provides that a carbon monoxide alarm should be fitted when a new or replacement solid fuel appliance is installed in a dwelling.
Is there an SEAI grant for a boiler stove?
SEAI does not currently offer an individual home energy upgrade grant for solid fuel stoves. Check seai.ie for the current list of supported measures.