If the furnace is located in a garage or closet, and the building has a crawlspace, the return is generally above the furnace and the supply is below. In other words, air is being forced down from above, into the crawlspace-duct system, and then into the home.
This is what we call a "downflow" or "downdraft" system.
Conversely, if the return side is physically at the bottom of the furnace, the cold air enters from below, the furnace heats it, and the hot air is propelled into the supply side above the furnace. Basement furnaces are configured in this manner; this is called an "upflow" or "updraft" furnace.
Both up and downdraft furnaces are mounted vertically. But what if the furnace were mounted in the attic or crawlspace? These require horizontal mounting. (An older furnace engineered to run vertically could not be installed in a horizontal position. It would start a fire. ) A furnace pulls air across the filter, through the blower, around the heat exchanger, and into the exhaust system. It has to be in that order.
But, again, traditionally, the burners were always located below the exhaust system, allowing the exhaust products to vent upwards through the heat exchanger. Because of this need to always vent exhaust products upwards, each furnace had to be specifically designed for the application intended. You could not turn over an updraft and use it in a downdraft configuration.
With newer induced-exhaust systems, and "shot" burners that force air through the heat exchanger rapidly, the exhaust system can be physically located beneath the burner (incidentally these newer "shot" burners are part of the reason many less expensive newer furnaces are so doggone loud).
Question is, is this good for the consumer? These convertible furnaces are usually the cheaper basic furnaces, so the cost can be reduced, but not likely enough to be significantly noticed by the end user.
I feel that these furnaces with exhaust at the bottom will be prone to more exhaust-inducer motor problems, condensation issues, blockages and so forth. But they are designed and approved to be completely convertible to any configuration.
Q: I am having my shower stall remodeled. Would you please tell me about the pros and cons of different materials for the shower pan, in particular about durability, leaking, etc.?
A: Fiberglass/acrylic pans are easy to clean, and relatively inexpensive. If not installed correctly they can squeak, or in rare cases get a hairline fracture.
A "mud-set" pan is labor intensive, but obviously very attractive when covered with tile. These can leak at the plumbing joint and corners when not installed correctly. The older lead-pan liners (beneath the cement) had a life of 20 to 40 years, while newer PVC models have had an unlimited lifespan thus far. Copper-impregnated mesh and other styles are also available, with mixed results.
Pans are also custom-fabricated from cultured marble, Corian-type materials and so forth. Relatively rare and expensive, they should hold up well if made of a material that is not overly brittle. Some of the more porous materials may not be the best choice as they may be difficult to clean.
Darrell Hay answers readers' questions. Call 206-464-8514 to record your question |
