Frequently Asked Questions
Q - What is a masonry heater?
A - A masonry heater is a wood burning appliance used for home heating. It absorbs the heat energy from a short duration (about two hours average), very hot fire. This stored energy is slowly released in the form of healthy, radiant heat of a long period of time, up to twenty-four hours in some cases.
The Masonry Heater Association (MHA-net.org) defines a masonry heater as the following:
“A masonry heater is a site-built or site-assembled, solid-fueled heating device constructed mainly of masonry materials in which the heat from intermittent fires burned rapidly in its firebox is stored in its massive structure for slow release to the building. It has an interior construction consisting of a firebox and heat exchange channels built from refractory components.
Specifically, a masonry heater has the following characteristics:
- a mass of at least 1800 lbs,
- tight fitting doors that are closed during the burn cycle,
- an overall average wall thickness not exceeding 10 in.,
- under normal operating conditions, the external surface of the masonry heater, except immediately surrounding the fuel loading door(s), does not exceed 230′ F “.
Q - How is a masonry heater different than a traditional open fireplace?
A - A masonry heater differs from a fireplace in several crucial aspects. These differences produce a much more reliable, clean, and efficient wood burning appliance.
- Firebox – The firebox is smaller and the geometry is designed to reflect the fire’s energy back upon itself. The fire in a masonry heater is hundreds of degrees hotter than a traditional fireplace. A properly designed firebox can produce nearly complete combustion of the wood fuel, say 95-98% of the energy in the fuel is consumed (please note, this is not the over-all efficiency for a masonry heater).
- Air control – The air entering the firebox is tightly controlled by a simple slide damper under the firebox and another simple slide damper controlling the chimney draft. Unlike the large open door of a traditional fireplace, a heater’s firebox doors are air tight. The air entering the firebox carefully regulated and directed to promote good, optimal conditions for clean combustion. The goal is for just enough air for clean burning without extra air to cool the fire and masonry.
- Heat exchange channels – Unlike a traditional fireplace where the energy from the combustion exits directly into the chimney and out of your home, a masonry heater is built with internal channels that direct the hot exhaust gases throughout the heater before exiting into the chimney. These channels absorb the heat energy from the fire before they exit into the chimney and out of your home.
- Thermal mass – A heater is built exclusively out of masonry materials. The internal high temperature core and outer shell have a very high mass, up to 10 tons of masonry material. This large mass absorbs and stores the energy of the fire.
- Chimney location – Unlike a traditional fireplace, the exhaust chimney for a heater is not always directly above the firebox. The chimney for a heater is sometimes placed on either side or to the rear of the firebox loading doors. The energy of the fire is not sent directly up and out of the house, but directed through heat exchange channels first. It also isolates the core of the heater from the weight of a masonry chimney.
- Clean burning – A masonry heater is designed to burn cleanly. The hot firebox and internal shape of the heater are designed for nearly complete combustion of the fuel. This produces very little particulate pollution and nearly no contribution to greenhouse gases. The clean burn also prevents the creation of creosote or tar inside the chimney. Burned properly, masonry heaters need almost no cleaning, just a yearly removal of fine fly ash from the internal channels.
Q - Will a masonry heater produce enough heat for my home?
A - The amount of energy needed to heat every home is different. The total energy needed is called the “heat load” of a home. The heat load of a home is affected by such factors as the number and placement of windows, insulation R values in the walls and ceilings, or how tight the home’s envelope is. You can determine your own home’s heat load by reviewing heating bills from previous years or calling a local service for a home energy audit.
The heat provided by a masonry heater is entirely determined by the amount of wood burned. Generally, masonry heaters burn approximately 50lbs of wood every burn. With one burn a day this is equivalent to about 240,000Btu or 10,000Btu/hour over twenty-four hours. Burning the heater two times a day doubles the output to about 480,000Btu or 20,000Btu/hour over twenty-four hours.
As a radiant heat source, a masonry heater is most effective heating the areas it “sees” – rooms within direct line of sight of the heater. There is of course additional heating throughout the house, in the rooms above the heater for example, but the primary energy will be in the area open to the heater.
Anecdotally, there are modern, well-insulated, 2000-2500 sqft homes using masonry heaters as the primary heat source. Fire Works Masonry has two masonry heaters acting as the only heat source for the clients’ homes- our heaters in Rockhill, NY as well as Kutztown, PA.
In larger homes, or older homes with less insulation, a heater can create a warm, reliable comfort zone in the house. A secondary heat source is always needed in case you leave the home during the heating season and are not actively burning the heater.
If you would like to review the possibilities of lowering your own home’s heating bills, please feel free to contact Fire Works Masonry for a review of your home’s specific heating needs.
Q -Can a masonry heater be built into an existing home?
A - Yes, a heater can be built into an existing home. About one-third of our heaters are built into existing homes. It is however, obviously a large scale complicated remodeling project. A heater requires a significant masonry foundation underneath and a chimney (either a masonry or a metal pipe chimney) that will run over the roof-line. The decision to put in a masonry heater takes careful, detailed planning.
Q - Where is the best place to locate a masonry heater in the home?
A -The best place for a masonry heater is where the family spends the most time. A masonry heater is very pleasant to around. The fire is entrancing and the radiant heat is warms a body deeply.
A central location is also advantageous. It improves even heat distribution throughout the house.
Heaters are often used as room dividers. A heater between the kitchen and living room is a popular option. This provides the option for a bake-oven on the kitchen side with the loading doors on the opposite side in the living room.
The location is often influenced by the home’s existing design. The heater needs a large sturdy masonry foundation to support its large mass, so consider what is under your proposed location for the heater. For example, will a foundation disrupt a finished basement?
The heater also needs a chimney approved for wood burning appliances. Ideally, the chimney will remain inside the home’s envelope until it exits the roof. A chimney inside the home performs better and lasts much longer than one built outside the home on an external wall. So consideration must be given to venting the heater. Will the chimney location interfere with living space above the heater or conflict with the home’s load bearing members above?
Q - Can my existing, traditional fireplace be modified into a masonry heater?
A - Possibly. The best case scenario, the existing chimney can be used to vent the masonry heater. The large size required for the heat exchange channels as well as the fundamental need for a big masonry mass prevents a heater from being “inserted” into a fireplace like a metal stove.
Often modern traditional fireplaces and chimneys are located on an outside wall. The presents additional problems. Ideally, the heater and chimney as well as all the heat they retain are kept within the building. Fireplaces exposed to the outside present a challenge to insulate and keep the energy in your home.
Generally, there are two options with an existing fireplace;
1) Demolish the existing fireplace facade and build a masonry heater in front of the fireplace opening utilizing the existing chimney. If the chimney is in need of repair or unlined, a steel insert may be required for safety. The ne masonry heater will require a load bearing footing and foundation underneath to support the weight.
2) Demolish the entire existing masonry fireplace and chimney to the floor level. A masonry heater is then built on the existing foundation and a new (often metal pipe) chimney vents the new heater. The new chimney is run through the void created by the demolished chimney.
Q - Does a masonry heater require blowers or fans?
A - A masonry heater relies entirely on natural principles. Fans are not used to distribute heat and the heater relies only natural draft for combustion so no blower is used. A masonry heater works without any external power. A warm heater in daily use develops a reliable draft with every fire- the energy in the masonry from the previous day’s fire quickly creates a draft as soon as the chimney damper is opened.
With a masonry heater and bake-oven a family can always cook and be warmed by the radiant heat with no external power.
Fire Works Masonry