Guide to installing a WOODBURNING STOVE CLOSER LOOK Woodburners for hot water & space heating
Nigel Griffiths takes a look at the benefits of woodburners for delivering efficient space heating and hot water, and how to get your new stove installed
Nigel Griffiths explains the benefits of this popular home heating solution and outlines installation considerations
Above: The striking, Ecodesign-ready Studio 3 (from £3,439) is the largest woodburner in Stovax’s range, offering an 11kw heat output and widescreen views of the flames. It can be hearth-mounted or seated on the optional 180 steel bench (from £509). Right: This Valiant two-blade fan, from £75 from Ludlow Stoves, gently and silently distributes air from the hot zone around the room to improve comfort and reduce fuel consumption
Wood has been used as a fuel for cooking and heating since the dawn of time – and there can be little better than enjoying the cosy, calming glow of a real fire during the colder months. These days, most of us look to a woodburning stove to achieve this. A stove is far more efficient than an open fire, as the heat can be largely retained within the building – with less of the useful warmth escaping up through the chimney. So what should you look for in a woodburner, and how can you get the specification and installation right?
Types of stove
The simplest form of woodburner is a space heater. In other words, it’s designed to warm the room it’s located in. Your installer will look at factors such as the size of the room and amount of insulation in the building fabric to calculate the heat output required. You can then match that up with the many high-quality designs on the market.
Many homeowners choose to add a heat-powered stove fan to their installation. These are a smart idea, as they require no electricity to run. Instead, they make use of the heat differential between the base of the unit and top of the fan to drive a motor that aids heat distribution, warming up the room in a fraction of the time.
Some woodburners can also be used for cooking, potentially boosting sustainability. Whether this is viable depends on what sort of building you live in: a very small dwelling heated solely by a woodburner is an ideal candidate, for instance. The heat used in cooking is simply recycled into the indoor atmosphere after it’s past through pots/pans and their contents (although sophisticated designs can even include an oven). In larger homes, it’s unlikely you’ll want a primary source of heat to be concentrated in the kitchen – so it’s more common to use a stove solely as a space heater in a lounge or study.
Stoves can also be fitted with a back boiler, which enables a contribution to central heating, hot water or both. It slightly reduces the amount of heat dissipated into the room, but this isn’t normally an issue in well-insulated modern homes. Back boilers can provide warmth to a domestic hot water cylinder or an accumulator. These work slightly differently, and it’s important to understand the difference if you’re considering a woodburning stove. See the box (opposite) for more on this.
Why choose wood?
One advantage of using wood as a fuel is that it can be an almost
As we have got better and better at reducing heat losses in new buildings, space heating demand is now very low. This means hot water now represents a much more significant proportion of household energy usage. If you want your stove to provide domestic hot water (DHW) and/or central heating, you’ll need some kind of storage tank where the water can be warmed and stored. There are two main options to consider:
Hot water cylinders
With this setup, the heat from the stove passes through a coil in the cylinder, transferring to the water inside the tank. This is known as indirect heating. Cold water enters the cylinder at the bottom, has its temperature raised and is drawn off at the hottest point (the top).
Usually, there is at least one more heat exchanger in the cylinder, which is powered by a fossil fuel boiler, heat pump or – even better, I would suggest – a solar water heater. A twin-coil cylinder takes up no more space than an ordinary one, but does cost a little more. The hot water in the body of the tank is the water that actually comes out of your taps and showerheads.
Accumulators
Just as with a standard cylinder, heat is transferred indirectly from the stove into the accumulator – but thereafter, the process is a little different. The hot water is provided by means of a further heat exchanger. This means the water that flows to your outlets passes through a coil, entering as cold and picking up heat as it goes. So the DHW is separate from the water that sits permanently within the body of the heat store.
Another way to look at this is to say that a traditional cylinder stores hot water, whereas an accumulator stores heat. The fact that it uses water as its heat store is incidental – it could easily use a different medium, but it just so happens that water does the job very well.
An accumulator can also be used to provide space heating. Again, the warmth is drawn off through a further heat exchanger – either for a whole building or to specific zones, such as a bathroom and bedroom. It’s an ideal solution where you plan to use more than one source for short period of time. This would be the case with stoves and solar thermal, which should each have their own input as they work in opposite seasons: woodburning in winter; and solar when the sun’s out. This can yield near year-round zero carbon hot water (with a little backup from the boiler or heat pump).
Bear in mind accumulators are larger than domestic cylinders, so you need to plan for a little additional space and perhaps some extra structural support.