Mr. Heater MHT 45 Air For Combustion Residential, Outside Combustion Air Supply, Vertical Venting

Vertical Venting

Air For Combustion (Residential)

If indoor combustion air is to be supplied for a tightly enclosed area, one square inch of free area opening shall be provided below the heater for each 1,000 Btu/hr of heater input.

When outside air is used, the opening below the heater shall be one square inch of free area for each 4,000 Btu/hr of heater input. In contaminated atmospheres or high humidity areas, optional outside air for combustion is recommended.

Adequate clearances around the perforated fresh air plate must be maintained at all times. In larger open areas of buildings, infiltration normally is adequate to provide air for combustion.

Direct Outside Air For Combustion (Residential)

Outside combustion air should be supplied directly to the heater when the building is subject to negative pressure or contaminants are present in the building air. These contaminates include paints, solvents, corrosive vapors or any other foreign particles that may cause damage to the heater or result in poor combustion.

Outside combustion air can be brought directly to the heater by a 3 inch diameter duct less than 25 feet long or equivalent. This is attached to a 3 inch starting collar that is fitted on inlet side of the control cabinet. An approved vent cap must be placed directly to the end of the outside combustion air inlet pipe. The combustion air inlet should be a minimum of 3 feet, either vertically or horizontally, from the flue vent termination. The air intake terminal must be located not less than one foot above grade. It is good installation practice to supply combustion air from the same pressure zone as the vent outlet.

In colder climates, where necessary, insulate the fresh air duct. Avoid locating the fresh air duct directly above the control box. Provide a capped cleanout T as necessary.

VERTICAL THROUGH THE ROOF

Vent Cap

(Leslie VersaCap)

	3" Dia.
3' Min.	Single-Wall Pipe

6" Min.

Flashing
3" Starting Collar	¼” per ft.
	downwards

Intake Vent

Outside Combustion Air Supply

The MHT tube heater is approved for installation with an outside air supply system. Some compounds such as halogenated hydrocarbons or other corrosive chemicals in the air can be drawn into the equipment and cause an accelerated rate of corrosion of some of the heater components. The use of such chemical compounds near the enclosure should be avoided.

IMPORTANT: If the building has a slight negative pressure or contaminants are present in the air, an outside combustion air supply to the heaters is strongly recommended.

For an outside air supply a three (3") inch O.D. single wall pipe may be attached to the heater. The duct may be up to twenty five (25') feet maximum length or two (2') feet minimum length with no more than two (2) elbows.

The air supply duct may have to be insulated to prevent condensation on the outer surface. The outside air terminal should be securely fastened to the outside wall by drilling four (4) holes in the outside flange; wood screws or bolts and expansion sleeves may be used to fasten terminal.

Non-Pressurized Outside Air Supply Duct

Mr. Heater Gas-Fired Low-Intensity Infrared Heater 16 Operating Instructions and Owner’s Manual