ENLARGING THE GROUND FLOOR--Supplying Heat to the Room

You can usually extend heating ducts to an addition if your house has a conventional forced-air system. The average American house furnace is at least 20 percent bigger than necessary, providing ample capacity for the extra demand. For best results, have a heating con tractor help you plan the job.

An addition located against a part of the house that tends to be too cool poses special challenges. Extending the heating system may be possible if the added ducting will be relatively straight, allowing efficient air flow. But if several ducting turns are required, an electric heater will be more practical.

Duct Types: Ductwork comes in round and rectangular versions. Unless you plan to run ducting through a wall—a tricky installation that requires a gap in the subfloor and sole plate—choose round duct. Because both types are too big to pass through a header joist, you will have to make a hole in the masonry foundation to reach the addition; check a painted foundation for lead.

Ensuring Proper Air Flow: To achieve maximum air flow to the addition, attach the new supply duct to the main supply duct if at all possible: Tapping a room duct generally works only for a small addition. Provide return ducting as well as supply, building it in the same way (although where you tap into the existing return duct is not critical). If you need additional sup ply and return registers, run separate ducts for them.

Dampers are lacking in many home systems, but they are easy to put in and greatly simplify the task of balancing a forced-air system. Add dampers wherever supply ducts branch off the main duct.

Raising the Blower Speed: For more direct boosting of air flow, you may be able to increase the speed of the furnace blower. On most models, speed is adjusted with a switch or by changing wire connections. On any belt-driven blower, speed can be increased by replacing the motor pulley wheel with a bigger one or the fan pulley wheel with a smaller one.

If the furnace blower is already operating at the maximum desirable speed—very high speeds cause objectionable noise in the ducts— you can install an inexpensive booster fan inside the addition’s supply duct. Such a unit is wired in parallel with the furnace blower so that the two operate together.

TOOLS:

• Punch or electric drill
• Screwdriver
• Hammer
• Cold chisel
• Keyhole saw

MATERIALS:

• Round ductwork
• Damper
• Sheet-metal screws
• Duct tape
• Duct elbows
• Trim collars
• Masonry nails
• Metal straps
• Register boots
• Register covers
• Take-off collars
• Duct insulation

1. Installing a damper.

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Place a damper in the sup ply duct section that will be closest to the furnace.

• In a common model (photograph), the damper is held in place by two shafts, one of which is spring loaded. Drill or punch holes for the shafts on opposite sides of the duct, at least 6 inches from the plain end—that is, the end that is not crimped.

• Set the fixed shaft into one of the holes. Depress the spring-loaded shaft and push the damper into place. Release the shaft so that it extends through its hole.

• Attach the damper handle, following the manufacturer’s instructions.

SAFETY TIPS --- Work gloves protect your hands from ductwork’s sharp edges; add safety goggles and a dust mask when cutting through masonry.

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2. Assembling the duct run.

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• Slip the plain end of one section over the crimped end of another; plan the run so that the crimped end points away from the furnace.

• Punch or drill a hole through both sections on each side of the joint and fasten the sections together with sheet-metal screws.

• Cover the joint with duct tape.

• Continue adding sections until the run is complete. Turns—there should be as few as possible—can be made with simple elbows or short sections of flexible duct.

3. Cutting a path into the addition.

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• Chisel out a hole the size of the duct through the foundation wall and into the addition’s crawlspace, positioning the hole just under the sill plate and between two floor joists.

• Fasten sheet-metal trim collars to both sides of the hole you have chiseled, using masonry nails.

• Run the duct through the collars and hang it from the floor joists with metal straps .

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4. Completing the run in the addition.

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• Working underneath the addition, mark the opening for a register on the underside of the addition subfloor, using the rectangular end of a 90-degree register boot as a template.

• Drill holes at the corners of the out line, then cut the opening out from above with a keyhole saw.

• Bend the flanges of the boot flat and insert the boot through the hole. Nail it to the floor.

• Fasten the round end of the boot to the end of the duct run.

5. Tapping into the main duct.

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• Turn off the furnace and, using the rectangular end of a take-off collar as a template, mark and cut out an opening in the main duct.

• Push the tabs of the collar into the opening you have cut, and fold them back against the inside of the duct.

• Drill or punch holes through the flanges of the collar. Fasten it to the duct with sheet-metal screws.

• Fasten the round end of the take-off collar to the duct run.

• When all supply and return ducts are complete, turn on the furnace to check for air leaks at the joints. Wrap the finished runs with duct insulation to prevent heat loss.