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Boiler stoves that heat radiators: what are they?

When you first look at a solid fuel plumbing diagram it can, if you are not a plumber, look a little daunting. This section of the Stove Fitter’s Manual is designed in such a way that, should you read it step by step, you will gradually build up a picture of a circuit a little at a time. Then, when you look at a plumbing diagram for “a typical system” you will understand it (hopefully). It is really not complicated.

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What is a boiler stove?

Simple bolt-in 2 pipe stove back boiler. Looking at the stove from the front: the smaller flat panel on the left faces against the rear wall of the stove with the small protrusion passing out of the bottom left of the stove. The bigger protrusion would pass out of the top right of the stove. The angled large panel takes the full heat of the flame. The panels are hollow.

A wood burning or multifuel stove can, if it is fitted with a boiler, be used to heat a cylinder of water (for domestic hot water such as taps/bath/shower etc.) and/or one or more radiators.

A boiler is a metal box with water in it (it’s that simple) – it can be as simple as a cavity that is bolted within the stove.  This box will have two (or four) pipes that protrude through the rear of the stove ready to be attached to plumbing pipes. This style of boiler might be pre-fitted within the stove or sold as an add-on for the customer to fit themselves.

A stove might be designed with a “water jacket”. in this case the body of the stove has a cavity that can be filled with water (usually this cavity is in the rear and sides of the stoves and hence a common term for these boilers is a “wrap-around boiler”).

Stoves with boilers should never be lit without being connected to water.

Boiler stoves are connected to cylinders or radiators using copper pipe and usually supplied with water from a header tank (often in a loft).

stove with four port back boiler

Is a boiler stove right for my situation?

There are a number of things to consider and we will look at these briefly below:

Firstly: A simple boiler stove system (oft called a wet system) is, in my opinion, a wonderful way of heating a home. The technology is very simple and there is very little to go wrong. Adding self-sourced fuel to a cosy fire and having hot water and a few rads fire up is very satisfying.

There is no such thing as free energy: I often hear people say “well the stove will be running anyway so might as well have a few rads running off of it”. Well you cannot create energy from nothing. Each item connected to your stove needs energy and energy is created by burning logs (or smokeless fuel). If you put X amount of logs on per hour you will warm the room the stove is in. If you want to heat one radiator you will be adding X logs more, two radiators XX logs more, plus a cylinder XXX logs more. Stoves, radiators and cylinders eat fuel. If you have access to free wood (some landowners do) then things are looking good – but remember that it requires chopping and storing and drying. A house that has five or six radiators and hot water requirements can easily use a stacked wheelbarrow full of wood over a long cold day. I have fitted two boiler stoves to a property with 20+ radiators (the guy owned his own copse). I have also fitted a stove with no cylinder and just four radiators.

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Cost and upheaval: A typical wet system can take two people between one and two weeks to install (depending of course on many factors). Some floorboards often have to be taken up. A heat sink radiator usually has to be added (one rad that is always on if the stove is on). In my opinion cost is usually higher than people envisage. The easiest properties to deal with are small properties and those where one can start a system from scratch (e.g. a gutted property), especially properties with no existing heating system. Integration with existing systems is complex and will add difficulty and expense. Rarely have I fitted a boiler stove in a nicely decorated suburban home (maybe its the upheaval or possibly the mentality or maybe just the fact that they more often than not have access to mains gas?).

Can I integrate with my existing boiler? Almost always the answer is yes. But the cost and upheaval and space requirements will likely put you off (is the usual outcome in my experience). You can read more about this subject on this website.

Fitted incorrectly a boiler stove can be very dangerous. The main reason for this is that when water boils it turns to steam and increases in volume over 1600 times. If the steam has no escape route (suitably sized vent) then the stove or the circuit will explode. Another danger is if a system overheats to such an extent that water in a loft header tank boils and the tank collapses. All this is avoided if systems are correctly designed and safety features added.

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