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Energy Saver: Furnace, Boiler & Woodstove Combustion
(continued ...) joints with aluminum tape.
I've talked about duct in a number of previous paragraphs. Let's quickly go through some good practice items if you're the do-it-yourselfer. First, 'duct' means rigid galvanized metal duct; no flexible duct is allowed. Everything you need can be bought at your local home center. Stay with round duct except where it is just not possible. Round is the most economical shape. Square is next most economical but harder to work with. Rectangular de-rates capacity versus the area of duct. Plan your route.
Each fitting adds the equivalent resistance of 10 linear feet (300 cm) of duct. Keep fittings to a minimum. If your equivalent length (with fittings) appears to be more than 100 feet, you should probably increase up one size from what the Building Department official told you. Joint construction should be with 1/8 inch (0.3 cm) diameter by 3/16 inch (0.5 cm) long pop-rivets. Rivets are better than any type of screw. Drill three into each joint roughly equally opposite. Wrap the joint with 2 inch (5 cm) aluminum tape. Fabric 'duct tape' is for fixing lawn chairs and golf bags; not ducts. Carefully press all the air bubbles out. Be sure to cover your rivets. Be sure to cover every joint including articulated elbow joints. Alternatively, you can use duct mastic to seal all the joints. In comes in a small bucket or caulk tube and dries to flexible and air tight. Support the duct about every 10 feet (300 cm) with wire or punched metal tape.
The last thing to reduce energy, related to combustion, is maximizing heat exchanger performance. Again if you are reading this, you are ...