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Refractory Fireplaces
Install Them Correctly

By John J. Pilger

Maybe it started with a call from a customer who was having problems with his fireplace damper. When you pulled up in front of the house, you noticed that there was no cap on the chimney. The homeowner said he had just purchased the home, and when he went to start a fire, the damper wouldn't open.

The fireplace was a Heatform metal fireplace, and upon inspection, you found that the damper area had rusted out, leaving large holes in the fireplace's metal smoke chamber where the fiberglass insulation was exposed. You turned to the homeowner and told him the bad news: the fireplace had to be replaced.

Or it could have happened this way: A customer asked you to check out an old fireplace. She complained that the fireplace never worked that well and the room was always cold. When you arrived, you noticed that the old firebrick was deteriorated and needed to be replaced.

Or maybe you were called to a home built around the turn of the century, and when you inspected the chimney, you noticed there is no liner. No problem, you'd reline the chimney. However, after measuring the fireplace opening and calculating the square inches of the flue opening, you found out that you couldn't fit the proper-sized lining system in the existing flue because it was too small.

These are just three instances of problems that can be solved by installing a precast modular masonry unit, also known as a refractory modular fireplace system. There are different manufacturers and names for these units (Bellfires, Frisch-Rosin,

Firecrest, Firecast, and Heatforce to name a few) all based on the design of Dr. Peter Rosin. And in this article I'll refer to all of them as Rosin-design fireplaces.

First, Some History

The earliest fireplaces were nothing more than a large, open fire from which the smoke would escape through an opening in the roof. When chimneys were first developed, the fireplaces were very inefficient and produced little heat.

Around the turn of the 18th century, Benjamin Thompson, Count of Rumford, began to ponder the vast amount of smoke in the room whenever he lit a fire in the fireplace, and began a series of experiments to improve their performance.

After a series of trials, Thompson concluded that the exaggerated width of those early chimneys was a main cause of smoking fireplaces. He attributed the problem only to the width of the throat, and not the whole chimney. Using the knowledge gained from his studies, he modified the traditional fireplace design into a hotter, cleaner-burning fireplace that did not smoke.

That's how fireplace burning technology stayed for many years. In fact, it wasn't until after World War I that the next breakthrough occurred.

Around 1939, Peter O. Rosin conducted a series of scientific experiments for the British Coal Board. In his report, "The Aerodynamics of Domestic Open Fires," Dr. Rosin was able to observe air and smoke flow patterns. He also discovered that Benjamin Thompson had been incorrect when he assumed that the smoke shelf deflected downcurrents of cold air back up the flue with hot gases streaming up the front of the chimney.

Rosin observed that hot gases streamed up the back in stratified layers, and in fact, a smoke shelf disrupted the efficient flow by causing turbulence. Through his laboratory work, Rosin was able to design the ideal shape for a fireplace to be much more efficient and functional.

Today's Rosin-design fireplaces are precast modular masonry units that include the precast firebox back, firebox sides, firebox hearth, and the precast or stainless steel smoke domes or chambers. The fireboxes are precast with industrial grade refractory material.

Some manufacturers reinforce their casting with stainless-steel needles and have extra-thick castings for maximum thermal storage (Bellfires). Some also incorporate outside air into their design (Frisch-Rosin) while another uses smaller, modular pieces so cracks will not develop (Heatforce).

On the modern Rosin-design fireplace, the apex, located on the back wall, creates a hot spot that radiates a vast amount of heat back into the fire and out into the room. The casting also stores a tremendous amount of heat, allowing firebox temperatures to elevate well above the range of the conventional fireplace. These high temperatures produce a very clean, complete combustion with no visible smoke emitting from the chimney top. The complete burning of the wood leaves a light ash, and creosote is practically eliminated, reducing the threat of chimney fires and eliminating the odor from a problem fireplace.

Installation: Here's When. . .

There are a number of reasons why you would install a Rosin refractory fireplace, including the scenarios described at the beginning of this article. You can replace rusted-out metal fireboxes, and allow a reduction of the fireplace opening from a 10-to-1 ratio to a 20-to-1 ratio (that's firebox to flue size) to allow for proper relining of the flue. This is a great help when the interior chimney dimensions restrict you.

The Rosin design also allows you to refurbish old fireplaces, convert small coal-burning fireplaces, and correct dangerous or unsafe smoke chambers and fireboxes in order to bring them up to modern-day safety codes.

. . .And How

Installation is not too difficult assuming, of course, that you have a certain level of skill. There are special tools you may need: an oxy-acetylene cutting torch for removal of metal fireboxes (an absolute necessity if you need to remove a metal

firebox), an exhaust fan for dust control, a demo hammer for masonry firebox removal, a tile knocking system, a heavy-duty circular saw with a diamond-tipped blade, and a winch to pull up the smoke dome.

Proper preparation of the job site is essential to keep the customer's home clean. Before you start, take a Polaroid picture of the room. When you remove items from the wall or move enough furniture to have a clear work area, you'll know where they have to go back. Now, put some drop cloths on the floor, and add sheets of cardboard on top of the drop cloths for extra protection. Don't forget to put down rug runners from the entrance to the work area and from the work area to the bathroom, including the bathroom floor. Cover all remaining furniture with either drop cloths or 3-ml plastic. Place a 4-foot by 8foot sheet of 1/2-inch or larger plywood over the hearth extension so it won't get damaged, and also protect the fireplace face with either plywood or ridged insulation panels. Finally, hook up an exhaust fan on the chimney top to control the dust and smoke associated with the firebox removal.

A safety reminder: When torching out a metal firebox, be sure to have a 21/2-gallon pressurized water extinguisher on hand and a person to watch for wayward sparks.

The first step to remove a metal firebox is to remove the damper. I use a Sawzall for this because the smoke shelf is generally full of creosote and sparks from the torch may ignite it. To remove the damper, cut the pins at each end. When the damper is removed, vacuum the smoke shelf clean, stuff the heatform vent channels with fiberglass, and duct tape the fronts closed.

Start your cuts in the upper corners of the firebox, just below the damper and down to the fireplace floor. Next, cut horizontally across the firebox just under the damper and again about eight inches from the floor. Remove that piece of metal and then cut the tabs holding the outer and inner walls together and do the same with the sides. Use extreme caution when removing the smoke chamber because it may be supporting the flue tiles. If you are removing a masonry firebox damper it may be easier to use an angle grinder with a carborandium blade or a Sawzall.

When the firebox is removed, be sure to check for exposed wood; it's not uncommon to find wooden studs or plywood inside the smoke chamber area or the sides of the firebox.

If flue tiles have to be removed to make room for the chimney liner, you can do this now. Be sure to cover the fireplace front with a sweeps cloth and a piece of plywood if you are going to remove the tiles from the top. If you want to remove the tiles from the bottom, the exhaust fan will control the dust.

Place a piece of plywood across the bottom half of the fireplace opening to block any debris from entering the room, and position yourself three feet from the fireplace opening. Insert the tile knocker to the second tile from the top. Now, using short bursts of the drill to avoid jamming your tool, start removing the tiles.

Next check the fireplace floor to se if it's level. If repairs to level it have to be made, do it at this time, using quickset cement. Remove any protruding or sharp bricks in the smoke chamber area and brick up all four-vent channels from the inside, if applicable.

Now that the firebox has been gutted, use refractory cement to adhere a one-inch, foil-backed ceramic blanket to the firebox walls, making sure that the foil is facing out. Insulate the rear of the refractory fireback with one inch of foil-backed

ceramic blanket, using either spray glue or refractory cement to hold the blanket in place. Use metal tape to seal all seams. Be sure to leave about twelve inches of blanket overlapping on each side so the firebox sides will be covered after they are installed.

You insulate the fireback and sides to retard the heat loss through the rear and sides of the unit. You must also insulate the stainless steel smoke dome with one-inch blanket, sealing all seams and wrapping it with stainless-steel wire. If you are using the precast masonry dome, however, you don't need the wire.

Next, wrap the flexible chimney liner with a minimum one-half inch of foil-backed ceramic blanket. Be sure to seal the joint with metal seam tape, then encase it with the protective stainless-steel sock. One tip to installing the sock is to take silicone spray or WD40 and spray the foil--the sock will slide easily over the liner. Install the sock clamp on one end, pull the sock as tight as you can, and install the second clamp. Wrap the liner with the stainless-steel wire, again pulling the wire as tight as you can. This will really help if you have a tight-fitting flue. Move the liner into the home.

Now, attach the insulated smoke dome to the liner using stainless-steel rivets spaced about 1-11/2 inches apart. Rivet the liner end cone to the liner and drop the winch cable down the flue. Hook the cable to the end cone and pull the liner and smoke dome to a temporary position above the firebox connection to make sure it fits properly.

You should lay out the center line of the firebox and the front reference lines by drawing a straight line at the front of the fireplace opening, then finding and marking the center of that line. Take framing square and place it on the mark in the center and draw a line from the front to rear. The center line is very important; if you skip this step, the casting maybe off center when you install it and this is very noticeable.

Find the center line of the firebox back and mark it. Carefully position the firebox back at the fireplace opening and gently move it into position using a wonder bar for leverage. Place a level at the top and sides to check for level and plumb.

If it's not level or plumb, you will have to shim it using a piece of stainless-steel sheet metal. Attach the firebox sides with flare retainers. Or, some installers use bricks mortared together to the rear of the sides to hold them into position. Do not cement the sides to the firebox back-in time, this joint will crack due to expansion and contraction. Be sure to use refractory cement on the outside of the firebox sides to the fireplace shell.

Once the sides are in place the rear of the firebox back and sides must be insulated with either thermix or perlite. If you use perlite, be sure to use proper dust control.

The next step is to cut strips of ceramic blanket (minus the foil) to act as a gasket between the casting and the smoke dome. Lower the smoke dome into position and anchor it to the firebox back using the hold-down straps. Rivet the smoke dome lintel into place, spacing the rivets about two to three inches apart.

Now you can insulate the floor with blanket again to retard the heat loss, and you can measure the front of the two-piece hearth (if applicable) and cut to size. I use an angle copier from the side panels to the fireplace face and make a template

out of cardboard and copy it to the hearth. Finally, install the top hardware along with a top damper, and the job is complete. Some installers paint the unit black and install a log retainer too.

Seasoning the Fireplace

It is very important to teach the homeowner the proper procedure for seasoning their new fireplace. You must light small, break-in fires. If you make a large, roaring fire in the beginning, you risk cracking the casting due to the moisture content in it. Build short, small fires in the beginning and work your way up to longer hotter fires. Contact the manufacturer for these important instructions.

While the steps outlined here are complete, installation can be tricky and difficult at times. I would recommend you attend one of the training courses provided by manufacturers or state guilds to get hands-on experience.

John J. Pilger, a member of the NCSG Technical Committee and member of both the National and the NY Chimney Guilds technical committees and on the Board of Directors of the Chimney Safety Institute of America, owns and operates Chief Chimney Services Inc. in Suffolk County, Long Island, New York.