Proper venting of Heating Equipment

February 14, 2017

Proper furnace and water heater venting is important not only for optimum performance of gas and oil-burning equipment, but for the health and safety of those living in the home. Many times when visiting a customer’s home to service or replace an aging piece of equipment, we find an improperly installed venting system. A customer will say, “It’s been that way for 25 years, why change it now?”

Because it’s wrong, and it’s unsafe.

Improperly assembled or terminated vent pipes, poorly sized or deteriorating flues, and other venting shortcuts can cause equipment failure, deterioration of building materials, fire, and even death by asphyxiation or carbon monoxide poisoning.

When gas is burned to make hegas-furnace-proper-ventat, waste gases are created and must be removed from the equipment. This is the job of the venting system. In a typical case, a smoke pipe connects the furnace or water heater to the chimney. Assuming the chimney is in good condition, the warm exhaust gases will rise up the chimney and escape into the atmosphere. The rate at which these gases move out is called draft, and under normal conditions, there should be enough draft to pull those gases up and out. If the chimney is falling apart, maybe bricks have fallen inside or the flue liner is cracked, or if maybe a bird has decided to build a nest in your flue over the summer (a common occurrence), there will be little or no draft in the chimney, and exhaust gases will try to escape elsewhere. Newer furnaces will have a spillage switch, which will shut down the furnace if it detects exhaust gases leaving the furnace in a location where they shouldn’t. Older furnaces don’t have this feature, and you could be inhaling exhaust gases if you weren’t aware of the problem. (Another reason to have your heating system serviced annually by Adirondack Mechanical’s trained service technicians!)

Modern high-efficiency gas furnaces have much different venting requirements than furnaces of even 20 years ago. A condensing gas furnace (any furnace with AFUE, or Annual Fuel Utilization Efficiency of over 90%) will create exhaust gases of about 130 degrees, or about the same temperature as your clothes dryer’s vent. This tem13fogged_up-highefficiencyperature is much lower than the condensing point of water (212 degrees), so water vapor changes into liquid water in the vent. When combined with the mildly acidic byproducts of burning fuel, this water becomes corrosive and would eat through any metal vent piping. This is why such furnaces are vented using a small fan and plastic pipe, often through a wall. Additional piping (and often a small condensate pump) are added to the venting in order to carry away the water collected from the vent. Depending on how the venting was installed, it may be necessary for you to keep snow and ice away from the vent termination on the exterior of your home. Snowbanks and ice buildup can clog the pipe, thereby restricting the passage of air in and exhaust gases out. These furnaces are very susceptible to even minor fluctuations in draft, and their venting systems must be installed in strict compliance with the manufacturer’s recommendations. Because of the many interdependent safety systems on a modern furnace, and in order to maintain utmost operational efficiency, it’s a good idea to have your condensing furnace serviced annually by Adirondack Mechanical’s trained service technicians.

Often when an older, inefficient furnace is replaced with a modern high-efficiency unit, there can be a problem with the existing water heater venting that didn’t exist before. Because an older furnace makes so much exhaust gas, and because that gas is so warm (sometimes over 300 degrees), there is usually little trouble getting a draft in an old chimney. Once that big lunk is removed, melted-plastic-at-draft-hood2however, the relatively smaller water heater isn’t large enough to heat the chimney and sustain a draft. You can see this if you look at the plastic rings around the hot and cold water connections on the top of the water heater. Do they look like they have started to melt? Then you have a draft problem with your chimney. The hot gases cannot be drawn quickly enough up the chimney, and they are escaping from around the draft diverter and into your home, melting the plastic around the piping as they travel past. This is an unsafe condition. It can be corrected by installing a chimney liner, which artificially shrinks the size of the chimney to a size adequate for the water heater. Depending on the age and condition of the water heater, you may want to consider a power vent model, or even a tankless wall-mounted model, either of which use a different venting method that does not use the chimney. Call Adirondack Mechanical’s office at 518-883-3077, and we will give you all the information on all of your options.