Q - I am concerned about having adequate combustion air for my furnace and the hazards due to backdrafting. How can I check it, and how can I supply combustion air to it? G.P.
A - Providing adequate combustion air (preferably outdoor air) to your furnace and water heater is very important for several reasons - furnace efficiency, potentially deadly indoor air, and your comfort.A 100,000 Btu/hour gas furnace running continuously for seven hours would consume all the air in a 860 square foot house. If your house is airtight and you are operating your clothes dryer or kitchen or bathroom vent fan, your furnace and water heater may not get enough combustion air.
The operating efficiency of your furnace drops when it is starved of air. Some common symptoms are yellowish flames, non-uniform flames that seem to "dance" on the burners, and soot around the opening of the furnace burner.
A lack of adequate combustion air may also cause deadly carbon monoxide (CO) to form. If it's severely short of air, the negative indoor pressure can draw the CO back down into your house. Inexpensive CO testing tablets for your house are available. Stick them up near your furnace and water heater and perhaps in your bedrooms. Check them often for color change.
To efficiently supply combustion air, you can build an enclosure around the furnace and water heater and duct outside combustion air to it. This not only solves the combustion air problem, but it reduces chilly drafts in your house. This is effective for a basement or first floor utility room.
A rule of thumb is that, for a vertical duct, you need 1 square inch of UNRESTRICTED free vent area per each 4,000 Btu/hour input rating. For a horizontal duct, you need twice that much. A coarse screen vent covering is acceptable. If you add metal louvers or grill, increase the overall vent area by a factor of 1.33. For wood louvers, use a factor of 4.0.
You can also use a combination of indoor air wall vents from adjacent rooms and a smaller outdoor vent pipe, 1 square inch of area per 5,000 Btu/hour Check with your furnace dealer about recommended clearances around the furnace when sizing the enclosure.
Don't just run an outdoor duct directly to the furnace opening. This can cause drafts into the furnace and combustion inefficiencies. The furnace may not operate properly with cold outdoor air ducted into the opening.
You can write to me for UTILITY BILLS UPDATE No. 259 showing schematic diagrams of enclosure layouts for providing all outdoor or out-door/indoor combustion air, a worksheet to determine if you already have adequate combustion air, and a list of suppliers of CO testing tablets. Write to James Dulley, The Deseret News, 6906 Royal Green Drive, Cincinnati, OH 45244. Please include $1 and a self-addressed business-size envelope.
Q - I am replacing my old deck. Can I burn the old and scrap pressure-treated wood in my fireplace without causing any problems? H.T.
A - You should never burn any type of pressure treated lumber. It has been impregnated under pressure with special chemicals to resist rotting and insects. Many of the chemicals can be dangerous to your health.
Proper handling of the wood shouldn't present problems. However, smoke from burning the wood and any airborne sawdust can release the chemicals into the air that you breathe. Also, repeated contact with your skin can be bad, especially from the penta and creosote preservatives. CCA-treated wood can give off arsenic fumes when it burns.