Question: We have a seven-year-old Rheem modulating furnace. Twice now we have had failure of the manifold gas valve because water from the air intake line dripped on the valve and corroded the contacts. The air intake line is right above the manifold valve. Would insulating the intake line remedy this reoccurring problem, or is there another solution? — Fred Soukoreff
Answer: Despite the many items in homes that can be successfully maintained by a diligent homeowner, difficulties with furnaces should be dealt with by a licensed heating, ventilation and air conditioning (HVAC) contractor. Modifications to HVAC systems can cause other problems or serious safety issues. Your focus should be on finding a competent technician with enough experience with your brand of furnace and a willingness to find a solution to your leaking issue.
There are many items and systems inside a home that require minor to moderate homeowner maintenance to keep them in good working order. Some of these may include regular painting, cleaning, adjustments and lubrication of doors, windows, flooring and other components. This should also include regular changes or cleaning of your furnace air filter and visual inspection of the heating system. Normally, looking for signs on the outside of the furnace housing of corrosion, leakage, moisture stains or unusually noisy operation is the extent of this task.
Since you have already had an issue related to moisture, you may also want to periodically remove the upper door on the front of the furnace enclosure to look for leakage. If water or excessive stains are seen on the components behind the removed cover, then further action may be required.
Anything past this point should be completed by an experienced, licensed gasfitter, due to the complexity and danger involved. Because your furnace is a natural gas-fired appliance, there can be serious consequences to malfunctions that could be life-threatening. That is why gas lines, meters and other associated natural gas components are the only major system homeowners are not allowed to modify or repair, even in their own home. If modifications are done incorrectly, the risk of natural gas, carbon monoxide or other dangerous products of combustion entering the living space is possible. This can make occupants very ill, or even lead to lethal situations in extreme conditions.
While it may seem like your idea of insulating the combustion air intake pipe is fairly benign, damage or blockage of this duct may lead to serious malfunction of the furnace. While it may seem like a bit of a stretch, numerous cases of homeowner harm over the years have been linked to seemingly minor items like that. Regardless, I will hazard a guess at a possible solution, but will caution that this should only be explored by a licensed professional.
All newer high-efficiency furnaces have small, plastic drain pipes due to the need to remove condensation from the units. These normally will terminate in a basement floor drain nearby, or in a small pump mounted on or beside the furnace cabinet. Because this drainage system is already in place, many newer furnaces that I see also have a second pipe, or set of lines, draining from the furnace. This second set is often to drain condensation associated with the exhaust or fresh-air intake piping. Because the exhaust from the furnace contains a large amount of water vapour, condensation is often a result, as it is blown out of the home to the cold exterior. The pipes may be sloped upward from the furnace to allow this moisture to run back downward, sometimes to a drip leg, or trap, that will allow drainage of the condensate. If this is not in place in your unit, it could be the actual culprit for your corroded components. I also regularly see evidence of leakage at the location where the exhaust pipe connects to the exhaust fan, often due to a loose clamp or deteriorated sealant.
If your problem does originate from the fresh-air intake pipe, it is likely that the air is very cold when it enters the basement, cooling the pipe and allowing the warm air from the home to condense on the pipe surface. This will normally occur on the exterior of the pipe, but could run toward the furnace if the slope is in that direction. Insulating the section of the pipe nearest the outside wall may help prevent this from occurring, but could also move the area of condensation closer to the furnace, as the insulation helps keep the pipe colder, further into the basement. Other possible solutions may include re-sloping the pipe, relocating the intake hood or location outside the home or sealing the pipe inside the furnace housing. There are likely other minor modifications that will prevent this issue from reoccurring, which are beyond my limited knowledge of the subject.
Quick fixes and small maintenance may apply to a number of components or systems in your home, but gas-fired appliances like your furnace do not fall into that category. Rather than attempting any of these for your problem, channelling your efforts into locating an experienced HVAC technician for your brand of furnace, who is willing to spend the time diagnosing and repairing your leakage issue, will be a more productive and safer use of your time.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home & Property Inspectors — Manitoba (cahpi.mb.ca). Questions can be emailed to email@example.com . Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.