General

A Temp-Cast 2000 fireplace and brick facade weighs over 6000 lbs (2720 kg) in most installations, not counting the chimney and concrete pad. Proper footings and foundations are required and existing supports must be inspected by a competent person before being used.

In a new installation, a footing must be poured on undisturbed compacted soil. A concrete block foundation is then raised and a concrete pad is poured on top of the foundation to the level of the unfinished floor.

The chimney is connected at the bottom of the heater and is supported by the same pad which supports the heater. For this reason, the layout of heater and its chimney must be decided before the footing and foundation dimensions can be calculated.

Chimney Systems

Temp-Cast heaters require at least 18 ft (5.5m) of 8"x12" (200 mm x 300 mm) or 8" I.D. (300 mm) round chimney. Clay, refractory and stainless steel liners are suitable. Both masonry and HT (i.e. "high temperature") factory built chimneys are acceptable.

Masonry chimneys should have liners that are laid with refractory mortar and are carefully aligned so that a ledge is not formed from one liner to the next. In addition, a 1/2" (25 mm) space should be maintained between the liner and the brickwork, for necessary expansion. The best liners have overlapping or "ship-lap" joints.

Every chimney should have provision for cleaning, with a tight fitting door near the base.

An existing chimney should be inspected by a qualified chimney sweep and approved by the local building official.

The chimney can be connected on either side or at the back of the fireplace. You may also want a "balancing" false chimney on an opposite side for aesthetics.

Chimney Draft

Chimney draft, that unseen force that we trust will cause smoke to rise up the chimney and out of the house, is the single most important aspect of good chimney design and the most overlooked.

Hot air (i.e. hot gases or smoke) rises because it is lighter than the air around it. In a chimney, this rising warm air (i.e. "draft") draws in oxygen to feed the fire. Without good draft, good combustion is impossible and smoke spillage is inevitable. Unfortunately, there are several factors which can defeat chimney draft. The three most common are exterior chimneys, negative pressure and the stack effect.

Exterior Chimneys

The greater the temperature difference between the air in the chimney at the stove connection and the air outside at the top of the chimney, the stronger the draft. (This is why smoke spillage and hard starts are more common in early fall and late spring, when the temperature difference between inside and outside is the least.) In addition, the longer this temperature difference can be maintained (i.e. the taller the chimney), the greater the draft.

A tall and warm interior chimney produces the best draft, while cold exterior chimneys cause stubborn lighting, smoky fires and chronic smoke spillage. For this reason, we do not recommend venting our fireplaces (or ANY combustion appliance) to a chimney constructed outside the warm envelope of the home. If a chimney in an unheated space is unavoidable, then an insulated factory built chimney is best, since it will heat up faster and keep the exhaust gases warmer for a longer period of time, improving the draft. (Ensure that the chosen chimney system can be connected with an approved masonry adapter.)

Negative Pressure & "Tail-Out" Spillage

Compounding the cold chimney problem is the air-tight design of some homes. In these homes, the air usage in the home is very tightly controlled. If make-up air is not sufficient, exhaust fans can de-pressurize the home, causing a negative pressure condition. In this case, air is drawn into the house from unexpected sources - down the chimneys serving the gas furnace, the fireplace, the wood stove, etc. This causes varying degrees of chimney failure. This can range from the fireplace that is difficult to start, to the wood stove that spills smoke whenever the door is opened, to the most serious, when a complete flow reversal brings smoke and gases down the chimney and into the home.

Flow reversal is the most dangerous because it occurs most often when the burn rate is at its lowest, at the start of a fire or at the end, when the burn rate has been slowed to preserve an all night fire.

In a typical metal wood stove, during the final stages of the fire, the firebox temperatures are slowly dropping. With this drop in firebox temperature comes a corresponding drop in chimney temperatures. In masonry chimneys, this drop is gradual. In prefabricated metal chimneys, the temperature drops as quickly as the stove. Eventually, chimney temperatures drop to the point that chimney draft is stalled - smoke is no longer being drawn up the chimney and can easily spill back into the living space. This phenomenon is known as "tail-out" spillage & is believed to be a common occurrence, particularly in basement installations and exterior chimney systems. It is of serious concern because it most often occurs during the night - when it is likely to be undetected and when occupants are most vulnerable - while they are sleeping.

A Temp-Cast masonry heater is not likely to suffer from "tail-out" spillage. The masonry mass retains enough heat to maintain adequate chimney draft for long after the fire is out, particularly with the recommended, centre plan chimney/heater combination. And since there is no need to burn the Temp-Cast at night, if spillage of any kind occurred, it would likely be immediately noticed.

Breathing combustion gases, especially carbon monoxide, from a wood or gas appliance, is a serious health hazard and can be fatal. (Even that "nice woodsy" smell associated with wood fires, caused by mild smoke spillage, is unhealthy and should be avoided.) Make-up or replacement air may be required in some installations - consult your builder or architect.

The Stack Effect

In many 2 or 3 story homes, another phenomenon which effects draft sometimes occurs, called the stack effect.

A good chimney system, as we have seen, will be a tall column or stack, insulated from the cold outside air, with an opening at the top.

If the warm air in the home has an easy access out of the house in the upper floors, such as through leaky windows, then the whole house may become a chimney stack - a tall column of warm air with an opening at the top.

With the stack effect, cool air is drawn into the home in the basement, through leaky walls, and doors (i.e. a "drafty" basement) or down the furnace or fireplace chimney. The warming air flows up through the middle of the house and exits near the roof. The stack effect can be mild, causing occasional spillage or it can be strong enough to create a flow reversal in basement chimneys.

Footings, Foundations & Floor Pads

The footing dimensions are 4" (100 mm) larger than the foundation dimensions in all directions. Ideally, it should be at least 8" (200 mm) thick and reinforced with 1/2" (12.5 mm) steel rod, laid in a grid pattern, 6" (150 mm) on centre, starting at least 3" (75 mm) in from the outside edges. The footing must be built on compacted undisturbed soil or another stable material.

A non-combustible cap, such as heavy gauge steel roofing or "wonder board", must be used on top of the foundation, to act as a form for the floor pad. The supporting floor pad upon which a single heater is built must be at least 6" (150 mm) thick and ideally have 1/2" (12.5 mm) reinforcing bar laid in a grid 6" (150 mm) on centres, starting at least 3" (75 mm) in from the sides. Provision must be made in the concrete floor pad for an air intake hole and an ash drop. (See Section 5.)

The floor pad can also serve as the hearth in front of the fireplace, required 16" (400 mm) in front and at least 8" (200 mm) either side of the loading doors, as detailed in the plans included in Section 5.

Outside Air Supply

An outside air supply is required in most new homes in North America. If required, outside air can be provided with an optional air intake damper and locally obtained pipe. A 6" (150 mm) round smooth duct is built into the top course of foundation blocks, which will feed necessary air into a 15" x 2" (380 mm x 50 mm) hole located in the floor pad, directly in front of the unfinished core. The duct is vented to the outside wall under the floor joists and can be equipped with an optional electrically operated damper. Activating the switch opens the damper to provide outside air for the duration of the burn and is closed when burning is complete. (At least 8" of air is required for "See-Through" fireplaces, divided equally between the two doors.) The intake should be installed on the windward side of the house, at the lowest point available.

In a basement installation with outside air, the fireplace can be installed on a raised hearth, if ceiling height permits. Air is then ducted into the raised hearth and fed to the front of the fireplace and into the door frame. If ceiling height precludes this option, a raised hearth can be constructed around the front and two sides of the fireplace and air is then ducted into it & then to the door frame.

In a basement installation without outside air, an optional air supply door is installed under the fireplace doors to direct air into the air slot. This will permit combustion air to enter via the air supply door, travel up behind the facade and enter the door frame to feed the fire.

Double-Stacking

When additional heat beyond the capacity of one fireplace is needed, two fireplaces can be built, one on top of the other, on two different floors of the home.

Double stacking fireplaces in this way saves the expense of separate footings and foundations, since they share one footing and the lower fireplace masonry work acts as the foundation for the upper fireplace.

In addition, two flues can be contained in the same chimney, for additional labour and material savings. The fireplaces then work independently of one another and may be fired alternately or together (draft permitting.)

Footings in this case should be 12" (300 mm) thick, with 2 grids of 1/2" (12.5 mm) reinforcing bar 6" (150 mm) on centres. One grid is placed in the bottom third of the footing, and the second is placed in the top third. The lower fireplace facade is carried to the ceiling level, a non-combustible support such as metal roofing is placed on top, and the floor pad for the upper fireplace is poured over it.

Chimneys for Double-Stacked Fireplaces

When double-stacked units are being considered, each must have its own flue. Chimneys for double-stacked units can be placed on left and right sides of the two heaters, or can be located at the rear of the fireplaces. In each case, the chimneys are supported on the lowest level. The flues continue through the concrete floor pad of the upper fireplace but the brickwork of the lower chimneys stops just above ceiling level and the upper floor pad is poured on top of these bricks, around the flue tiles. This allows the lower chimney brickwork to act as the support for part of the upper floor pad and chimneys.

Furthermore, each chimney flue must only service one fireplace and may not be connected to any other appliance.

Ashes for the upper unit in a double-stacked installation can drop to a concrete ash pit on top of the lower fireplace. They are accessed by a recess formed by the mason in the top of the lower fireplace. It must be equipped with a tight-fitting door. Alternately, ashes can be removed by lifting out the fire-grate in the upper firebox.

Whatever method is chosen for handling ashes, care must be taken to ensure that the air intake function and ash clean-out are physically separated, to prevent excess air entering the firebox via the ash drop hole under the fire-grate. Excess air into the fire from below may increase particulate emissions, and defeat the door air-wash system.

Dampers

A chimney damper is recommended in all installations to maximize the heat-storing ability of the fireplace and to ensure strong chimney draft at start-up.

The most effective chimney damper is a "roof-top" damper. It is installed at the very top of the chimney, and is controlled by a stainless steel cable. The cable is routed down through the chimney flue and is attached to a bracket in a convenient location near the heater. Its main advantage is that it seals the entire length of the chimney, trapping warm air inside. This provides an extra boost for quickly establishing a strong draft. It also acts an impenetrable chimney cap to keep out rain, snow, birds and animals, and prevent down-drafts caused by strong winds.

We also strongly advise that a carbon monoxide alarm be used in conjunction with all chimney dampers, as an extra margin of safety if the damper is closed prematurely.

Clearances & Buildings Codes

Although Temp-Cast fireplaces are efficient heaters, they are also site-built masonry fireplaces constructed of refractory components and as such conform to national building codes in Canada and the United States.

We don't recommend that you enclose your Temp-Cast fireplace in any type of wall, since you will be hindering some of its radiant ability. However, if a wall enclosure is unavoidable, we recommend clearances of 4" (100 mm) to combustible construction on the sides and back of the fireplace and 10" (250 mm) clearance overhead. Combustible materials should not be placed within 48" (1200 mm) in front of the fire doors.

In most jurisdictions, masonry chimneys and most factory-built chimney systems require a clearance to combustibles of 2" (50 mm) from top to bottom.

NOTE: a combustible wall with non-combustible material applied directly to it without an intervening air space IS STILL A COMBUSTIBLE WALL FOR PURPOSES OF CLEARANCES. If clearances must be reduced, a simple method is to build a wall behind the fireplace, in the area of concern, constructed of "Wonderboard" (a 1/2" [12.5 mm] cement sheet) installed on metal studs. This wall section must extend 8" 200 mm) beyond the sides of the fireplace.

Wood Storage

Temp-Cast fireplaces perform equally well with softwood or hardwood, lumber scraps, branches, or bundles of twigs, up to 50 lbs (22 kg) per firing. The only requirements are that the wood be dry (20% moisture or less) and suitably sized. Ideally, the pieces should be approximately of the same diameter for maximum efficiency. Reserve larger pieces (up to 6" [150 mm] diameter) for adding when the firebox is fully heated.

Outdoor wood storage must ensure that the supply is loosely stacked (criss-cross or "log-cabin" style is best) so that air can circulate around all pieces. The wood supply should have a roof to keep off rain and snow and should also be open enough to allow good ventilation.

Improper storage may prevent the wood from drying to the proper moisture content of 20%. Wood that is not dried to this level of moisture may create excess air pollution and impair the heating ability of the fireplace.

Planning Summary

You should now be able to consider all these variables and sketch the fireplace, chimney, supporting floor pad, foundation and footing. (Keep in mind it is generally easier to build a rectangular pad than one that tries to follow the shape of the heater-chimney-hearth footprint.) For your convenience, we have included several of the most common plan designs and details.

Additional Sources of Information

"The Book of Masonry Stoves", by David Lyle, is considered by many to be the most comprehensive book written on masonry heaters. (click here to order it)

The Canadian Government also has an excellent publication, "A Guide to Residential Wood Heating", from Energy Publications, Canada Communications Group, Ottawa, Ontario K1A 0S9. (Fax 819-994-1498)

Involving Professionals
Many homeowners are able to successfully plan their own fireplace installations with this booklet and the included plans.

However, for special requirements, you may also want to consider the services of a professional. Your architect and contractor are experts in their various fields who can provide essential services.

Please contact us directly if clarification of any point is needed or if you would like to receive our installation and promotional video.

Due to variance in soil, seismic, and other local conditions, we recommend that you confirm all dimensions for footings, foundations, floor pads and clearances with your local Building Authority.

Section Summary

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