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1.6 Planning Ahead
Important to note:
1. Observe proper combustion air requirements.
2. Provide a firm support system for the chimney fan.
3. Determine the type of system involved.
4. Observe proper safety measures are taken to assure system will shut down in case of insufficient
draft in vent system.
Combustion Air Requirements:
Provisions for combustion air must be in accordance with applicable
local codes.
If the heating system is installed in an unconfined space,
adequate air will be available via normal
infiltration.
If the heating system is installed in a confined space,
(a space with a volume of less than 50 cubic feet
per 1000 Btu/hr of input for all fuel burning equipment) or building construction is unusually tight, adequate
air for combustion must be provided by two openings: one located about 6” below the ceiling, the other
about 6” above the floor.
Each opening must have a minimum free area as follows:
1. One square inch per 4000 Btu/hr of input when communicating directly with the outside or through
a vertical duct.
2. One square inch per 2000 Btu/hr of input when communicating through horizontal ducts to outside.
3. One square inch per 1000 Btu/hr of input when ventilation air is provided by openings in doors, etc.
to adjoining spaces having adequate infiltration.
Warning:
Adequate fresh air must be provided for combustion; otherwise, improper operation and inadequate
venting of deadly flue gases may result.
Support system for the chimney fan:
Prior to installation of the chimney fan, it must be assured the
chimney can safely carry the weight of the chimney fan.
A steel chimney should be well supported at the roof penetration point. If the chimney extends more
than 20’ above the roof, the chimney and the fan should be secured by wires attached on the chimney
and on the roof at 2 to 3 different points.
Brick chimneys usually do not need any kind of support to carry the weight of the chimney fan.
System Type
To determine the type of system is important in order to understand what to expect from the system.
Direct connect oil or gas appliances (no draft hood) normally do not require any mechanical draft
adjustment. However, if there are long horizontal breechings and far between the appliances, it is a good
idea to install mechanical vent-dampers, so adjustments of the draft can easily be made.
Draft hood systems should generally speaking have vent dampers installed. The vent dampers are used to
balance the system and assure that only a minimum of dilution air is pulled through the draft hoods.
Safety Devices
Local codes usually require installation of safety devices, when mechanical draft is provided in an oil or
gas fueled system.
Make sure a differential pressure switch (fan proving switch) is installed to assure that no appliance will
fire unless there is a proven draft.
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