Open Fires, Draughts and Chimney Dampers in the UK

If you’re reading this in the States, I’m probably preaching to the converted, but you will be surprised to hear that chimney dampers are all but unheard of here in the U.K. I’ve been involved in chimney/fireplace consultancy for nearly 15 years and I’m amazed this simple technology has not yet become a part of standard fireplace and flue design in my country.

Most people have never looked up their chimney; many have no idea that vast quantities of their expensively heated air are flowing through that fireplace, up the flue, and into the atmosphere 24/7 whether the fire’s lit or not. The fact is that leaving a flue open all year round is really no different to leaving an upstairs window open, come rain or shine.

Ironically, when the weather turns cold, people will often start to go round the house looking for the gaps around doors, windows, and even keyholes that are letting the draughts in, and trying to plug them, without much thought to where the draught is going to! Very often its the chimney that’s driving the draught, sucking that cold air into your centrally heated home.

In the U.K, building regulations specify that permanently open, dedicated ventilation should be provided for every open fire equal in area to half the cross sectional area of the flue. While homeowners are frequently appalled by the prospect of such a gaping hole in their living room, a fire does need to “breathe” and improvements in home heating efficiency such as carpets, double glazing, and draught proof doors mean we can longer rely on a purely adventitious air supply. Adequate ventilation need not be the cause of any discomfort if correctly located, especially if a chimney damper is fitted to the flue, preventing unnecessary draughts and heat loss when the fire is not in use.

When the fire is lit an appropriately sized vent will supply the air necessary for combustion, and to allow the chimney to draw; ideally it should not be within the fireplace, but on the same side of the room as the fireplace, so that the incoming cold air doesn’t cut across everyone’s ankles as it’s drawn to and through the fireplace opening and up the chimney. In fact, allowing the fire to “breathe” easily through this vent will tend to stop it having to suck air from further afield, through doors, windows or down other chimneys in the property, and improve comfort levels. Vents within the fireplace are less than desirable, as they may blow ash and smoke around and out of the fireplace; there is also a beneficial effect on the draw resulting from the incoming air coming through the fireplace opening, tending to draw smoke with it.

As the cost of heating our homes soars with escalating fuel prices, and the effect our wasteful habits are having on the environment become ever more evident, energy efficiency is no longer just an issue for green activists, but for all of us. For many, installation of a woodburning stove is the obvious choice, but in Great Britain we are lucky enough to have a rich architectural heritage of splendid open fires, and there is a good argument for preserving them, if we can minimize their negative impact on home heating efficiency. While woodburning or multifuel stoves have an important role to play, fitting them correctly very often involves lining the flue which is not only a costly operation for the customer, but can be irreversible, preventing use of the fireplace as an open fire in the future, and altering the character of the room forever. Those who have several fireplaces may well choose to have a stove fitted in one fireplace as their main supplementary heat source, and fit dampers to their other fireplaces, especially if the alternative is to permanently cap the chimney.

For fireplaces that are expected to be used on a very occasional basis, d.i.y. solutions can help. I often see plastic bags of fibreglass or bubblewrap stuffed into flues! There are also purpose made balloons and the like on the market but for more regular use, most would not choose to have to remove and store any form of sooty chimney plug every time they have a fire. It’s also worth noting that it’s good practice to allow a trickle of air to flow up the chimney, to prevent condensation, and/or a flue so cold it will be hard to re establish an updraught on lighting a fire.

Whenever possible, the ideal solution is to fit a purpose made chimney damper that the householder can instantly open and close at will, with no fuss or mess. The benefits in comfort and reduced fuel bills will make it an investment that pays for itself a lot faster than most in the home improvement sector. Dampers can be fitted at the top, or bottom of the flue, and there are pros and cons for both styles, but often the geometry of the fireplace and chimney, and the relative difficulty of access to the top of the chimney stack will be the deciding factor.

One reason the U.K. has been slow to adopt chimney dampers is undoubtedly the variety and age of our housing stock, meaning that off the shelf products may not be suitable for many homes, and it should be noted that if a poorly sized damper is fitted that, in its open position reduces the flue area significantly, it may lead to a smoking fire.

There are also many British fireplaces struggling to draw through the addition of a chimney pot. Although seen as “traditional” by many, they’re really a Victorian invention, suited to the smaller fireplaces popular from that period onwards. I’ve lost count of the times I’ve been asked to look at smoking fireplaces, and looked up the chimney to see a nicely constructed gather, and a good sized flue, which is abruptly reduced to less than ½ its area by an 8″ or 9″ pot, which itself is often partially obscured by slates or whatever other bearers the fitter has used during construction.

The combination of turbulence caused by the abrupt change in section and the physical restriction of the small outlet often causes these fireplaces to smoke unnecessarily. Another common “problem fireplace” is the 3’squarish opening revealed by keen homeowners who think they’ve peeled back the layers of history to find the original fireplace. What they’ve actually found is the builder’s opening, never intended to function as fireplace, but to accept a cooking range or Victorian style insert fireplace, built with a flue to match these more modest proportions.

In fireplaces where the flue outlet errs towards the undersized, I would not advise fitting a damper to the existing terminal. If access, and planning considerations allow, open it up, and extend the stack if necessary, or fit a bigger pot if you must, and fit a damper while you’re up there. Otherwise, try to fit a damper in the gather just above the fireplace lintel.

Chimney top dampers have the advantage of keeping birds and weather out of the chimney, as well as maintaining a warmish flue. On the downside are issues of access and working at heights, and the possibility of mechanical failure in the “remote control” operating system. (normally stainless steel cable or chain)

Fireplace dampers normally give you failsafe and visible mechanical opening and closing, and can be fitted without access to the top of the chimney, but are deceptively tricky to design and fit so they don’t foul the walls of the flue as they open, or overly restrict the egress of smoke from the fire below. Fitting is an awkward and sooty job…and if there isn’t a good bird guard up top, twigs and soot displaced by weather and bird activity can accumulate to get dumped on the hearth when the damper’s opened. By the way – mesh stretched across the top of the chimney is NOT a bird guard. It’s a perch/social amenity for our feathered friends to gather on while they keep warm, de-louse, defecate, and practice twig throwing! A good bird guard has a smooth, solid, ideally angled (to shed rain/snow and make perching a chore) top, and mesh sides.

I look forward to the day the majority of U.K. homes have dampers fitted to all their open fires, and predict that in years to come these devices will become as integral to responsible and shrewd home heating management as a well insulated loft, or double glazed windows.

Chimney dampers may not be fitted to flues serving gas fires in the U.K, nor may a gas fire be fitted to a flue or fireplace incorporating a damper unless rendered inoperable. The damper on a solid fuel/wood fire should not be closed unless the fire is out and cold!