Question: My son lives in a 100-year-old house. The main floor is 769 square feet and the second floor is 348 square feet. The second floor is not used or heated. At some time a 10-foot square basement was dug under the centre of the house to accommodate a furnace. There is no heat vent in the basement, but the cold-air return duct has a vent at the furnace. The heat duct runs through a two-foot high crawl space to the living room area, but there is no return vent in the living room or anywhere in the house. It may be covered by the carpeting. Last year, the furnace was replaced with a high-efficiency furnace with a continuous-running fan. The furnace contractor said it did not matter if the cold-air return vent in the living room was exposed, but I am not convinced. Should we lift the carpet to expose the vent? Should we leave the basement door ajar so the cold air can be sucked down into the basement? The furnace seems to be operating well and heats the house well. I enjoy reading your column and your advise will be appreciated. -- Helen Lymburner
Answer: Modifications to older homes, whether newly completed or in the past, often pose logistical dilemmas not found in newer construction. It may be fairly simple to add a return-air register in your son's home, but access to the crawl space may be the key to successful installation.
Forced-air heating systems in homes typically have two sets of ducts and registers. One is for the warm air, which is forced through the ducts by the furnace blower. Every homeowner will be familiar with those, as they feel the heated air emanate from the registers in various rooms. The second, often misunderstood set of ducts and register is for the return air, often called the cold air. This system is less obvious because cool air near the floor is automatically drawn into the registers, which may be partially hidden by furniture or other items. The return air improves the circulation of the heating system by supplying the furnace ducts with replacement air for the next cycle. If there are not enough return-air registers and ducts, the furnace will draw air from other sources, namely the basement and crawl space. That may pose some concerns, not only for performance of the furnace, but health issues as well.
Since there are limited return-air supply mechanisms in your son's heating system, the furnace must draw this air from some location. Some of it will undoubtedly leak into the existing ducting through gaps or cracks in the home's floor or walls, but most may come from the area below the main floor. Especially with the register cut into the return-air duct adjacent to the furnace, the majority of this replacement air will come from the basement and crawl space. If this area is clean, heated and the crawl-space floor is well sealed, there may not be much of a concern. If the crawl space still has exposed soil, contaminants contained in the soil will likely be drawn into the furnace to be circulated through the home.
These contaminants may include moulds, fungus, dust, bacteria and other potentially harmful items regularly found in soil. Moisture from the exposed soil may also raise the relative humidity of the air entering the heating system, adding to any potential mould-growth issues. Leaving the basement door or hatch open may allow more air from the living space to enter the furnace, but may not prevent unwanted basement products.
Installing additional return-air ducting will be beneficial to improve air circulation and reduce circulation of contaminants, but a couple of other repairs can be done, regardless of that upgrade. Installation and regular replacement of high-quality furnace air filters will help trap some of the airborne particles and prevent them from circulating through the home. This will only be effective if the filters are changed regularly to prevent blockage and strain on the furnace blower. The other area to address is the crawlspace soil, if not already well sealed. Installation of a continuous layer of six mil, or heavier, polyethylene sheathing over the entire crawl space will prevent excessive moisture and other products from entering the air in the crawl space and subsequently, the living space. This poly should cover the grade beam or perimeter walls of the crawl space, and be caulked to the floor joists and underside of the floor with acoustical sealant. It should also be caulked around any partitions or support structures within the crawl space. This step will be tremendously helpful, even if it is not practical to install return-air ducting.
Installing the return-air system may be fairly straightforward if there is enough room beneath the main floor to work in the crawl space. The return-air ducting is normally installed between the floor joists, or often uses that cavity as the duct, so the direction they run may also have an impact on the ease or difficulty of installation. Ducting can be run below the joists, but that may be tricky with limited room above the floor of the crawl space. Installation of registers in the living room, and other rooms on the main floor, may only require cutting holes in the floor or bottom of the partition walls, to create openings to the new ducting.
Installation of return-air registers in all the rooms on the main floor of the house in question will undoubtedly improve warm-air distribution from the furnace. The degree of difficulty will depend on ease of access to the floor above the crawl space, but sealing the soil in this area may be the most important factor in improving indoor air quality in the home.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and president of the Canadian Association of Home & Property Inspectors - Manitoba (www.cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at www.trainedeye.ca.
trainedeye@iname.com
