Hearth-mounted fireplaces are generally defined as those which are installed at floor level and set either within a stone or wood mantel or flush against a tiled, stone, brick or other non-combustible surface.

A hearthmount stove is an option for upgrading the performance of a masonry fireplace and is an alternative to a fireplace insert. Hearthmount wood stoves are mounted in front of or inside the fireplace and vented through the fireplace throat. They must also be vented through a stainless steel liner that is continuous to the top of the chimney.

Hearthmount stoves are usually more efficient than an insert as heat from the casing comes directly into the room. The certification label and installation instructions indicate if the unit can be vented through a fireplace.

History and Past Problems with Hearthmounted Wood Stoves

In the late 70s and early 80s, during another energy crisis where oil and gas prices were sky high, everyone thought they could  install a wood burning fireplace insert or a hearthmounted wood stove in their home and benefit from cheap heat.  Basically, hearthmounted stoves were “shoved” into the fireplace opening and vented through the existing fireplace chimney.

It was not until there was a dramatic rise in the number of house structure fires where fireplace inserts had been installed that the authorities decided to investigate this more closely.  It was discovered that there were some very large inherent issues associated with installing a wood burning fireplace insert in such a fashion.

In a nutshell, the flue of the fireplace was oversized to properly vent a stove.  When it comes to venting technology, bigger is not better.  In fact, it can be downright dangerous, sometimes resulting in deadly consequences.

A wood stove insert typically vents through an exhaust flue opening 6″ in diameter (some stoves may use an 8″ flue), which is 28 square inches.  A fireplace flue is built, at a minimum, with a ceramic or clay flue tile that is 11″ x 11″ inner diameter which equates to 121 square inches.  This is approximately four times the flue exhaust area that is needed to vent the stove correctly.

Temperature Variance within the Flue Stack

The hot smoke and gases that exit the stove at a normal temperature of 600-800 degrees are travelling through a much colder masonry chimney flue system.  Smoke travels upward in a spiral. A brick chimney’s flue is square or rectangular. Therefore, smoke is continually colliding with the flue walls on its journey to the outside. This is called “resistance to flow” and anywhere that the hot smoke touches the cold surface of the flue it will condense and stick.  This sticky mess is called “creosote” and is now the perfect fuel for a chimney fire.

Creosote in chimney

Since 1991, the Canadian wood burning installation code has required that a stainless steel chimney liner be installed from the flue collar of the wood burning insert and/or hearthmount stove to the top of the chimney.  The code permits alterations to the fireplace to let the installer create a clear route for liner as it passes through the throat and smoke chamber of the original fireplace.  For this reason, a good insert installation should be considered permanent.  Installed correctly, the insert should not need to be removed from the fireplace for many years because the liner and all the hardware supporting it is corrosion-resistant stainless steel.

Where the liner passes through the fireplace throat (the damper, smoke shelf area), it should be sealed to the masonry, either stuffed with mineral wool or with a sheet metal plate. A good seal in this location prevents cold, smelly air around the liner from migrating into the room.

This improvement in the design of insert installations has improved their performance to the extent that today’s best fireplace inserts can be almost as efficient as free-standing wood stoves. If you already have an insert installed in a masonry fireplace, the addition of a stainless steel chimney liner can improve performance and is mandatory per the fire code legislation.

In the 29 years since the Canadian code changed to mandate full liners for inserts and hearthmounts, they have become among the most trouble-free of all wood heating installations. This is because the liner runs almost straight up from the insert flue collar, which is the most desirable arrangement for reliable draft.  Cleaning the flue is a simple matter of removing the cap and running a brush down to the insert.

The reliability of an insert installation depends on a perfect installation.  If the liner connection at the insert flue collar is faulty causing the liner to fail, the results can be very messy.  Knowing all the ins and outs and pitfalls of insert installations is a job for professionals. Don’t make the mistake of thinking that installing an insert is a simple matter of running a liner up the chimney.  Contact the most experienced insert installer you can find. You won’t regret the small additional cost.

Words of caution regarding stainless steel liners

One thing of importance to note is that the stainless steel liner must meet the stove manufacturer’s recommendations for installation, clearance and proper venting.  That being said, certain older hearthmounted stove manufacturers have long gone out of business and it may be quasi-impossible to find user manuals.

Also, a majority of these older hearthmounted stoves are most likely not certified by a recognized safety authority such as ULC or Warnock Hersey.  If that’s the case, the best approach would be to upgrade the hearthmounted stove to a newer, certified model.

Lastly, older hearthmounted stoves, for the most part, had larger vent openings, i.e. 7” or 8” and current legislation (CSA B365) allows for a maximum 6” stainless steel liner.  Again, if a larger liner, say 8”, meets the stove’s recommendations for installation, clearance and proper venting with adequate draft, then there is no issue even though this conflicts with B365.  As there can be ambiguity between the manufacturer’s recommendation and the actual legislation, we strongly recommend that you seek the services of a professional installer to discuss your needs.

stainless steel liner attached to back of stove
Manufacturer data plate on lower stove front

What is the cost to install a stainless steel liner?

The average cost of a stainless steel chimney liner is around $625 for a ready to install, 6″ x 25″ foot flue liner kit and DIY installation. Professional installation of the same chimney liner kit with insulation is around $2,000.

Final Thoughts

Do NOT confuse these two different types of fireplaces when considering a hearthmounted stove:

Masonry fireplaces

Chimneys are constructed on-site from stone or brick and mortar and are part of the homes structural design. Typically, these fireplaces and chimneys are built as the house is built.  This type of fireplace can accommodate a hearthmounted stove AS LONG AS the stainless steel liner is installed to proper fire code AND meets the stove manufacturer’s recommendations as noted above.

Pre-fabricated fireplaces also known as a Zero Clearance fireplaces

Generally has a firebox of cast refractory panels, and usually some metal is visible in the room all around the firebox. If you look up past the damper, you will see a round metal chimney. And above the roof is more round metal chimney, sometimes surrounded by simulated brick housing. If you have a metal (zero clearance) fireplace and metal chimney, your options are very limited for a hearthmounted stove. Only a few inserts are tested for use in these pre-fab fireplaces. Check with your local Hearth retailer and confirm the installation clearances with the manufacturer’s literature. DO NOT TRY TO INSERT A WOOD STOVE INTO AN EXISTING METAL FIREPLACE!

Insurability

As mentioned earlier, many older hearthmounted stoves may not be safety certified by a recognized authority.  Certain insurance companies will refuse to insure a non-certified wood burning appliance.  We recommend that you check with your insurance company to verify what their criteria is for insuring a residence with a wood burning appliance.

Are hearthmounted wood burning stoves still available?

The short answer is yes.  Many of the older models found in upgraded fireplaces during the 70s and 80s have been discontinued as the manufacturers went out of business.  Today’s top three brands still available for sale are Majestic, Regency and Napoleon.  Again, it’s best to consult a professional to ensure that the new stove CAN be inserted into your masonry fireplace.

Looking for additional information on fireplaces and other wood burning appliances?  Take a look at our other articles on wood stoves, wood pellet stoves, masonry fireplaces, pre-fabricated fireplaces and Heatilator fireplace Inserts.