Throats, Voids and Fire Lighting
Throats, Voids and Fire Lighting
Problems with Hooded Pots
Terminals are sometimes fitted to the pot which can both reduce the flue below the legal minimum as well as being unable to be cleaned. These are usually described in Building Regulations as being unsuitable for use.
A classic example of these is the hooded pot insert. The hooded pot is a curved tile on top of a ring which is inserted into the pot.
Where these reduce the internal bore below the 8" minimum, they should not be used for open fires.
As they cannot be cleaned in the normal process of sweeping, they should not be used over gas or oil appliances.
Finally, when fitted to unused chimneys they do not prevent the ingress of vermin like jackdaws which can then build nests in the flue. Sadly these are very common.
Throats and Voids
Fireplaces should be well throated. That is to say that the void of a fireplace (that transitional volume between the fireplace opening and the flue) should taper gently and smoothly so as to maintain a smooth, laminar flow of smoke into the flue. Anything that interrupts this creates turbulent, chaotic flow, and that will slow the flow and can do so badly enough to create backpressure problems.
Where the void is boxlike and without taper, especially where the flue pipe actually projects down into the box, these problems can be severe. They can lead to preferential deposits around the base of the liner, causing the build up of soot which will interfere with the proper function of the flue. A similar problem can happen at the top of the flue where the pot is markedly smaller than the flue, and lacks a smooth taper.
Lighting the Fire
Lighting fires is another problem area. Traditionally, we use paper, with twigs on top, and then we add larger pieces as we go on.
1) First things first; we need to stop using paper. Being mineralised, paper makes thick fluffy ash flakes, and these can obstruct the flow of air through the fire.
2) Build the fire upside down. Put the coal or larger wood at the bottom so that it forms a reasonably solid mass, and will catch everything that falls onto it. (This enables it to catch all the small embers that form from the burning of the kindling, and which would otherwise fall through the bars of the grate and be lost. By using this method, the embers will fall onto the wood/coal and create a hot heart to help the ignition process along.)
3) Then put the large kindling on base, the smaller kindling on top of that, and on the very top place a small fragment of firelighter (I use only a quarter of the firelighter) plus some very small kindling.
4) Light the piece of firelighter and the fire will burn down faster and cleaner than the conventional technique.
This method has one stunning advantage: We have all, at one time or another, lit a fire that has failed to catch light. We then have to demolish the fire and rebuild it form scratch. This is possibly the dirtiest job known to man, and usually results in creating a terrible mess, leaving one black to the elbows. Been there, done that and didn't like it.
Using the upside down method, if the fire shouldn't catch, then all is simplicity and cleanliness. Simply add a few more small kindling scraps, another quarter of a firelighter, and off we go again. No mess, no fuss, and no dirty hands.
THIS REALLY WORKS. Trust me, I'm a chimney sweep.