QUESTION: This is a question on furnaces. Do we need a cold air intake to the furnace with forced air electric heat? Most of the questions you receive pertain to gas furnaces.
Thank you, Doreen Backer
I am currently building a 1,000-square-foot bungalow cabin. I have done all of the work myself, but have come to a point where I need some help. I would like to put in electric forced air heat with an HRV unit, which is requested by code. The problem is, I have no real expert knowledge in this field. I have looked on the net to find information regarding installation, code, etc, but have not found any. If you could forward me information as to where I could find the answers to my problems, or answer my question with your own expertise, I would greatly appreciate it.
Thank you, Ken Jakilazek
ANSWER: Both of your questions relate to buildings heated with forced air electric units and proper ventilation associated with this type of heating system. While they are not identical, I will address both issues of fresh air intakes and HRV installations for this type of system.
Fresh air intakes, for the provision of combustion air for heating appliances, are not necessary for electric furnaces. These are normally installed near an older natural-gas furnace or hot-water heater to ensure adequate air for combustion. These intakes are usually composed of long, insulated, flexible ducting installed with a loop near the bottom. This loop is designed to provide a partial trap, reducing the amount of cold air intrusion until it is needed by the heating devices.
In newer, high-efficiency units, the fresh air intakes are directly connected to the furnace combustion chamber with a plastic pipe to provide outside air without cooling the entire room where it is situated. Since electric furnaces heat using a series of electric elements, with no combustion of gases, no fresh air intake is required.
Regardless of the lack of necessity for combustion air for homes heated with electric furnaces, bringing in a good source of fresh air may be equally or more important than for homes heated with gas. Homes with older, naturally aspirated furnaces and water heaters have large chimney flues or vents installed to remove the products of combustion from the living space. These vents operate by automatically mixing a large amount of dilution air from the home with the exhaust products from the heaters.
This warm house air will normally contain a lot of dissolved water vapour, which exits the home along with the flue gases. Because of this loss of large amounts of moisture up the chimney, there is less chance of high relative humidity in the home during the heating season. With electrically heated homes, either forced air or other types, high relative humidity can be a problem because of the missing chimney.
The reason to install a good method for proper fresh air intake into a home of this type is to prevent excessive moisture and to allow stale, house air to escape. Installing a fresh air intake duct, similar to that mentioned earlier for gas appliances, directly connected to the furnace return air ducting is the traditional method to accomplish this.
If your home is older, with leaky windows and doors and good bathroom exhaust fans, that may be all you need to provide adequate ventilation. In the case of newer homes, as in the second question, a more aggressive method of ventilation may be required.
Heat Recovery Ventilators (HRV) are mechanical devices designed to accomplish proper ventilation, while reducing the amount of heat loss associated with regular intakes and exhaust fans. These units provide an excellent method for proper ventilation and may be a good choice for both of your homes, but may have limited capabilities in older homes where ducting is partially enclosed in walls and floors.
The reason little information is available to the general public on HRV installation is because it should only be attempted by qualified personnel. Proper installation of a ventilation system is complex and should not be attempted by amateurs, for the same reasons as forced air heating systems. Detailed measurements and calculations are required to ensure adequate heating and ventilation without oversizing requirements. Proper ducting, controls, wiring, intakes and exhausts are necessary for the safety and health of the occupants of the home. While you may feel confident enough to complete the majority of the construction requirements of your new cabin, HVAC should not be one of those attempted.
At the risk of insulting you and some members of the HVAC trades, I will let you in on a frequent observation during many of the home inspections I have performed over the last decade-plus.
The majority of the HRVs I have seen are installed improperly or with malfunctioning or disconnected controls. Some of these defects can be attributed to amateurs, but many are done by licensed HVAC technicians who are supposed to be trained on proper design and installation.
If these professionals are confused by installation of these systems, what chance do you think you may have to do a proper job? I think this issue can only be attributed to the same lack of information you have noted, which may limit the knowledge of installation personnel. This does not excuse the poor installations seen, as good courses are available through colleges and HVAC training institutions.
The good news is that every year, as installation of HRVs become more and more popular in our area, less defects are seen with installations.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the 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
