Pellet Stove Hearths

Pellet stove hearths do not have the same requirements as for other stoves such as wood and coal burners. The way that a pellet stove works is different in that the stove body does not get as hot as other free standing stoves that rely on radiation and convection to transfer the heat.

The other main difference is that the fuel is fed internally from the hopper, so the stove door does not need to be opened when the stove is operating to feed it which reduces the size of pad needed in front of the stove

These factors result in less stringent requirements for a pellet stove hearth pad than for other stove boards

If the pellet heater is being installed on a floor of concrete, stone, brick or another non-combustible material, no stove board is needed at all except for decorative purposes to highlight the unit or for framing, separating it from any combustible floor coverings.

The area around the pellet stove that the pellet stove hearth pad needs to cover will typically be six inches at the front and sides, less at the rear although it should extend under the vent pipe. The manual for your heater will give precise dimensions, which local building codes may exceed. Always go for the larger dimension in the interest of safety.

Another aspect that will determine the size of your hearth pad is the unit dimension of the decorative tile or stone it is to be covered with. Good planning will reduce the amount of tile cutting you have to do.

A hearth pad, ( also known as a stove board ), should never be placed on top of a floor covering such as carpet or linoleum. Floor coverings should be removed under the area of the pad, which should be placed directly on the floor itself.

If you're fitting an insert or a free standing pellet stove to an existing fireplace, you may need a hearth extension depending on the size of the existing hearth, and the amount of space the pellet heater takes up.

Pellet Stove Hearth Pad Insulation Values

Typically, manufacturers guidelines for a pellet stove hearth pad only say that the stove should be installed on a non-combustible surface. If the manual for your appliance says different, that's the figure you should use. Some pellet stoves are supplied with a built in steel hearth pad that relies on creating an air gap between the pad and the floor.

When looking at the 'R', (insulation, the higher the 'R' value the better), values of various materials, some surprising results can be found. Most natural stone has an R value around 0.1 for a one inch thickness, while a horizontal dead air space of 1/8 in. has a value of 0.92. increase the depth to 1 in. and the R value of a horizontal dead air space only goes up to 0.97. Ventilate the one inch horizontal air space and the value goes up to 1.43.

Cement board and ceramic board a quarter of an inch in thickness has an R value of 0.1, similar to natural stone. 2.25 inches of brick has a value of 0.45, while one inch of sand or gravel works out at 0.59. Ceramic tiles have a low R value of 0.01.

By sandwiching different materials in the hearth pad, the R values for the materials used can be added up to arrive at the total insulation value of the hearth pad.

The relevant UL Standards for hearth pads are:
UL-127 Standard for Factory-Built Fireplaces,
UL-1482 Standard for Solid-fuel type Room Heaters,
UL-737 Standard for Fireplace Stoves,
Fireplace inserts complying with the applicable requirements specified in UL-737 and UL-1482.

Building Your Own Hearth Pad

Pellet stove hearths need to be able to support the weight without bending or distorting which could cause cracking, as well as providing heat insulation for the floor.

If all you need is a hearth extension for a pellet insert, which doesn't have to support any real weight, this can be made virtually flush with the surrounding floor by removing the floor down to the joists, packing between the joists, and building up again to floor level with non-combustible material.

If you want a flush pellet stove hearth, the timber packing between the joists will have to be a lot more dense to support the weight of the stove.

Most pellet stove hearth pads are set onto the existing floor. Commercially made pads will usually have a plywood base, and be put together with latex modified cement. This construction is mostly to avoid damage in transportation. Plywood is definitely flammable. If starting on your own floor, cement sheet is a good base for tiling or flagging.

If using dry build techniques, it's recommended that a sheet of 24 or 26 gauge steel is included in the sandwich to avoid the possibility of sparks working down through any cracks to the combustible floor. If laid using cement, a steel sheet is not necessary.

When using fastenings between the layers, stagger them and don't penetrate more than the layer immediately below because long through fastenings could provide a path for heat transfer.