Fire Chief® / Shelter® Filter Box Assembly Instructions


The optional return air filter box is designed to filter the air returning to your out - side wood furnace from inside the house. The filter box comes with one (12”) start - er collar and one pre-cut plate and screws to seal one of the (12”) round openings to allow the air to be drawn in from the rear or top.

Instructions for installation:

This filter box is designed for interior use only. Do not install outside the home.

A return air duct is crucial to a balanced air flow for your furnace and must be installed or the furnace will not perform. Caution: Never reduce the return air duct size less than 12” round or (113 sq. in.). Reducing the return air flow will restrict the hot air flow and will cause excess strain on the blower motor.

The filter box can be placed in a basement or in the living area of the home.

If the living area is your choice, the filter box should be placed in the center of the home. This will allow air to be pulled from the heat ducts in an even flow.

If the basement is your location choice, the filter box can be placed on the floor or attached to the floor joist.

Install a 12”round backdraft damper to the return air filter box to keep air from reversing when the furnace isn’t in use. Always change filter every thirty days or sooner if needed. A dirty filter will restrict air flow and could overheat your outdoor furnace or damage the blower motor. Filter size is 16” x 20” x 1”.

HY-C Company LLC – 10950 Linpage Place, Saint Louis, Missouri 63132 For a look at HY-C’s complete catalog of chimney and fireplace accessories, visit us at


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