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Fireplace Repair and Chimney Maintenance
Fireplaces and woodstoves can be an effective secondary heat source for your home if energy-efficient equipment is used.
Although fireplaces were once considered a major source of heat for the home, they are now used mainly for decorative purposes and as supplementary heat sources. Unless your fireplace uses the latest energy-efficient equipment, it can only be considered an inefficient source of heat. It will also use a significant amount of the warm air from the house for combustion, defeating the purpose of using a fireplace as a supplement to your home heating system.
Good maintenance practices are essential to ensure safe, efficient operation of your fireplace.
The biggest hazard in any fireplace is creosote build-up. When wood burns too slowly and too coolly, gases condense m the chimney and form a creosote layer on the flue. Creosote is flammable and can be ignited by sparks from the fireplace. The amount of creosote build-up depends on the type of fuel used, how hot the fires are and the size of the chimney. Wet wood, slow combustion and oversize chimneys add to creosote build-up.
CLEANING YOUR CHIMNEY
You can clean your own chimney with a stiff-bristled chimney brush and extension handles. You’ll need to clean the flue down from the roof and up from the firebox A mirror and a strong light will help ensure that you’re removing all the creosote.
Masonry chimneys and fireplaces should also be checked regularly for cracks in the mortar and loose bricks. They’ll need to be repaired for efficient fireplace operation.
Improving fireplace efficiency
There are several ways of improving the heating efficiency of your fireplace as well as protecting against removal of too much heated air from your house. Since almost two-thirds of the heat from a fireplace is wasted up the chimney (along with almost four times more air than is necessary for combustion), it is wise to take some efficiency steps to save on energy dollars.
While a fireplace screen can be essential to keep live sparks from flying out beyond the hearth, the screen can also rob up to 30 percent of the heating efficiency of a fireplace. A way to correct the situation is to use a screen that is higher than the fireplace opening and to place the screen as far away as possible from the fireplace face. This will allow extra heat to escape through the opening created at the top of the screen
A damper that functions improperly can be a major source of fireplace inefficiency. Inspect your damper regularly to ensure a tight fit when closed. This prevents warm room air escaping up the chimney when the fireplace isn’t in operation. The damper needs to be open when lighting a fire, to provide enough draft for combustion.
If your damper needs replacing, you might consider installation of a chimney-top damper. As the name implies, this damper is installed on top of the chimney, keeping rain out, retaining chimney heat and lessening creosote build-up.
Check your chimney regularly for creosote build-up. Excess creosote can be ignited by sparks from the fireplace. To keep the flue clean, a chimney brush can be worked down the flue from the roof and up the chimney
from the firebox. Also make sure you vacuum the smoke shelf directly behind the damper to keep it clean. If your chimney has any bends, which is the case with many of the modern metal chimneys installed with new fireplace units, make sure a clean-out trap is located at the elbow of the bend to facilitate creosote removal.
If creosote build-up is persistent, start building smaller, hotter-burning fires to burn the creosote off the flue. A hotter fire is a roaring fire that needs plenty of air to burn. Keep glass fireplace doors open, if you have them, to ensure enough draft.
To retain more heat in the room in which your fireplace is located, try burning coal. It offers almost double the heat capacity of the usual hardwood fuel. However, make sure it’s coal and not charcoal. Charcoal will emit toxic fumes.
Another way to deflect heat into the room is by using a metal heat reflector or fireback. Firebacks can be aluminum or foil, but most homeowners invest in the decorative cast-iron type, which is about 25mm (1in) thick. To install a fireback, place it against the back wall of the firebox, with the bottom edge resting on the hearth. Use masonry anchors and steel screw hooks or lag bolts threaded through lead shields drilled into the masonry to fasten the fireback.
Although glass doors covering the firebox opening will help prevent heat loss from the room, they will not add heat from a burning fire to the room. There’s a bit of a catch-22 situation with glass doors. They do prevent heat from escaping, but they also prevent a constant supply of air to the fire. This results in a slower, cooler-burning fire that creates the potential for faster creosote build-up in the flue. Try not to consistently burn a fire with the glass doors shut. Every third or fourth fire should be a hot fire, with glass doors left open, to help minimize creosote build-up. With the doors open, you’ll be providing a supplementary source of heat to the room. If sparks from the fire are a concern, put a fireplace screen across the opening, but remember that a screen reduces heat gain in the room. Most glass door units have built-in roll-back screens for this purpose.
Glass doors are particularly useful when the fire is waning and there’s no heat being given off from the firebox. If the doors aren’t closed, you’ll simply be losing heat from the room up through the open damper.
A word of caution: always keep the damper open until the fire is extinguished. Flames and smoke from even a smouldering log can produce toxic gases. The only escape route is up through the damper.
To maintain your doors, check them regularly for defects, particularly cracked glass. Although the glass is tempered and can withstand high temperatures, a build-up of soot and creosote will reduce the ability of the glass to withstand temperature changes. Clean the glass with a cleaner recommended by the manufacturer. And after a fire, make sure you clean the doors only when the glass has reached room temperature.
Replacing your grate with a tube grate is one way of gaining more heat from the fireplace. These grates are composed of C-shaped tubes with both ends exposed. A fire is built on the bottom portion of the grate; air is collected in the openings in the bottom tubes and circulates through the rubes. As it circulates, the air picks up heat and is expelled through the top openings in the grate. Some units have blowers to force the heated air into the room. Whichever type you buy, the top tubes of the grate must be flush with the fireplace face and sit no lower than 5cm (2in) below the top of the face. Otherwise the heated air will not enter the room but will be circulated within the firebox instead.
Combination units are available that provide the benefits of a tube grate and blower along with glass doors. These are efficient units, since they allow warm air to circulate from the fire into the room Even with the glass doors closed, they allow for good combustion, minimizing creosote build-up while preventing heated air from escaping up the chimney.
In both the tube grates and the combination units, you’ll need regular maintenance of the interior of the tubes. Any buiid-up of soot or creosote will prevent an efficient movement of air through the tubes.
Fireplace inserts are a popular means of getting more heat from the fireplace. The insert has a firebox enclosed in another box. Air enters not only the firebox for combustion but also the secondary box, where it circulates around the outside of the firebox, picking up heat and discharging it into the room.
WOODSTOVES
A freestanding woodstove or fireplace stove is an efficient means of adding heat to your home. Airtight woodstoves properly connected can produce almost six times more heat than a masonry fireplace
Most modern woodstoves are airtight and contain baffles and fans for efficient operation. A baffle divides the firebox into two sections, minimizing heat loss up the flue. A baffle also provides control for secondary combustion. Air enters the woodstove from a low air intake for primary combustion. Unburned gases move toward the rear of the stove and, if a baffle is in place, will not escape up the flue but will move toward the front of the stove underneath the baffle. Where another air intake allows for secondary combustion to burn off the gases, creating more heat and minimizing creosote buildup.
Follow the maintenance procedures under fireplaces to ensure a creosote-free firebox and flue.
FIREPLACE INSERTS
A fireplace insert draws room air through the bottom grate and circulates the air around the firebox and out through a grate in the top of the unit. As the air circulates, it is heated. Combustion air is brought into the fire chamber through a grille located at the bottom of the glass doors. While this type of unit does heat your room, it also provides for a cooler-burning fire, creating the potential for creosote buildup on the flue. Frequently burn fires with the glass doors open. This makes for a hotter fire and helps burn off creosote.
AIRTIGHT WOODSTOVE
A baffle divides the firebox of a woodstove into two sections, minimizing heat loss up the flue and allowing secondary combustion to take place.