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A Few Reasons Your Masonry Fireplace Doesn't Work
Why fireplaces work and how best to build them has been a topic for centuries. From the first stone rings stacked around the campfire to the modern factory built fireplaces with carefully engineered dimensions has been a steady evolution of design parameters to make sure they draw well and provide as much heat as possible. Most of this evolution has been by trial and error and some designs work much better than others.
Fireplaces work mainly because hot air rises. When you start a fire, the air inside the chimney becomes warmer and less dense than the air outside the chimney and consequently it starts to rise. As the warm air rises, cooler air from the room flows into the firebox, fanning the fire and creating more heat in an ongoing cycle. There is also some pressure differentials produced as wind moves across the top of your chimney.
There must be many reasons why a fireplace may not function properly and will try to cover some of the basics here starting with the obvious solutions and working towards the more arcane. The following is a very simplified list of the more common reasons that fireplaces don't work as should. An understanding of fireplaces requires extensive knowledge of airflow patterns, pressure differentials, and actual fireplace construction techniques. If the following information provided does not help you solve the problem with your fireplace, you need to obtain the professional services of an experienced WETBC (Wood Energy Technician of British Columbia), certified inspector, installer and/or chimneysweeper in your area. Often a fireplace and/or chimney problem is obvious to someone with enough experience once they can actually look over the entire situation.
Is The Damper Fully Open Or Operating As Intended? Everybody eventually forgets to open the damper or clean the damper area. Many dampers will cease to fully open because of water damage (metal parts of the damper form rust and corrosion), or soot buildup behind them on the smoke shelf. A good cleaning can usually solve this problem.
Is The Firewood To Green Or Wet? The main reason the fireplace works at all is the heat inside the chimney. If the wood is not dry and well seasoned it makes more smoke than heat and there simply may not be enough heat for the chimney to work properly.
Is The Chimney Dirty? The gradual accumulation of black soot (creosote) can seriously affect the way your chimney performs. Thick layers of creosote can physically restrict the flue in that there is no longer enough free area within the flue liner to vent the smoke from the fireplace properly. A 1/4" to 1/2" inch buildup can make more difference than you might think. Consider that a 1/2" buildup will restrict the airflow by 17% for a typical masonry fireplace chimney and by 30% for the average prefab. In addition to a dirty chimney, small animals and rodents can nest within the chimney during the non-heating season. Sweeping often finds a chimney literally packed full of leaves, twigs and baby animals and the solution of course is a good cleaning before and during the heating season and a chimney cap.
Is The Chimney Tall Enough? For a chimney to function properly, the chimney should be at least 10 or 12 feet in overall height. Where it projects above the roof, the chimney needs to be at least 3 feet high and at least 2 feet higher than anything within 10 feet of it including other buildings, trees, etc.
Is The Flue Large Enough For The Fireplace Opening? There are many variables that can affect this which could be; - The overall chimney height. - How warm the flue stays. - The throat configuration.
The basic rule here is that the area of the fireplace opening can be no more than 10 times the area of the flue (12 times for round flues). An undersized flue simply can't handle the volume of smoke produced and some could potentially spill back into the room. Since there is no practical way to make the flue size larger (if existing), the solution may be to make the room opening smaller with metal smoke guards or some additional masonry work. In fact there are now some premanfactured refractory firebox retrofits that work well with a 15 to 1 ratio and deliver more heat then conventional fireboxes.
Is The Chimney On The Outside Of The Building? Warm rising air is the basic engine involved here. If you have a large masonry chimney on the outside of the house and it's cold outside, the air inside of the chimney will also be very cold and it will want to fall down the chimney instead of rising. This can even happen a day or two after it's warmed up outside. These chimneys may be hard to start and they may smoke as the fire burns low. To help get the fire started many people light some rolled up newspaper and hold it up near the damper to get that cold plug moving upwards. Keeping a moderate sized but bright, actively flaming fire can also help this situation. Remember that as the fire dies down, it will revert back to the original direction of flow.
Is The Home Too Air Tight? Fireplaces require large volumes of air to burn. Visualize a 12" x 12" column of air rising up your chimney and exiting the top the entire time your fireplace is working. This air comes from inside the living area and must somehow be replaced. With modern energy efficiency concerns most houses have been carefully insulated and weather-stripped to keep out the cold drafts but an undesirable side effect is that there is often nowhere for all that air leaving the chimney to get back in. This can lead to fireplaces that burn sluggishly and smoke. A temporary solution is to open a window to let in a little make up air, preferably on the windward side of the house. It can also lead to very dangerous carbon monoxide buildup if your fireplace and furnace must compete for combustion air, and a permanent solution needs to be found at once.
Is The Home To Leaky? A house that leaks too much air to the outside especially a multistory house that leaks air in the upper levels can actually set up its own draft or chimney effect strong enough to overpower your fireplace chimney, particularly if the fireplace is located in the basement on a cold exterior wall. Be sure the attic access door is in place and that all upstairs windows are tightly closed.
Is The Return Air Grill In The Same Room As The Fireplace? As the fireplace consumes air and cold air moves into the house to replace it, the furnace is likely to come on. When the furnace comes on, air is drawn into the return competing directly with the needs of the fireplace. There are other reasons your fireplace can smoke and could be contributed to design problems when the fireplace was built. Aside from the chimney being too short, or too small, the chimney can also be too large, too tall, too crooked, damaged, deteriorated, etc. Most of these details are fairly technical in nature and generally; a good sweep may only be needed.
WETBC (Wood Energy Technicians of British Columbia). WETBC is the provincial governing body of the Wood Energy Technical Training Program in British Columbia. WETT is Canada's only system for training and recognizing professional competence in the field of residential wood burning. The program was developed to promote knowledge of and adherence to, the safety regulations governing residential wood burning systems among those who provide professional services to the public.
Since the first courses were offered in 1988, more than 3,000 people from all parts of Canada have participated. The members include Chimney Sweeps, Installers, Retail Sales People, Home Inspectors, Insurance Inspectors, Fire Suppression Inspectors and Building Inspectors Upon completion of the selected courses and the required experience level, all participants of the Certification Courses provided by WETT and their Provincial Affiliates must send in to the Provincial Affiliate Governing them a Completed Occupational Analysis Form. This acknowledges that the applicant has achieved the necessary field training and experience as decided upon by WETT Inc
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