Question: We’ve had many warmer winters since 2008 and the HRV intake frost problem described to you then was not always apparent, but in 2017, we happened to be home all winter and the old problem reared its ugly head again. This was long after your advice was followed to have the furnace/HRV installer check all fittings for the intake and exhaust hose. No air leaks were found, but hose connections were all resealed with tape.
I removed the quarter-inch wire mesh from the HRV intake hood and enlarged the mesh openings to a half-inch, to no avail. I then purchased mesh with three-quarter-inch openings and installed it, also without success. Eventually, I installed mesh with one-inch openings, with the same results. When the temperature drops below the -25 C range, the mesh plugs up solid with ice crystals within 24 hours after cleaning it.
I made a much larger rodent mesh with half-inch square openings. I don’t know what the smallest proper size would be to make this work, so I chose to make it bigger instead of smaller. And when the temperature was -25 C with over 50 per cent humidity outdoors, there was no sign of buildup of ice crystals anywhere on the rodent guard. I also added spray foam around the HRV intake hose between the joists, even though that had been done professionally at the time the house was built in 2007.
Now, on to the next tough question: what is your opinion about furnace floor-vent filters to reduce dust in the house? We had one bad experience with furnace duct cleaning and don’t relish the idea of doing that again. Are there other ways to reduce the floating and circulating dust in the house? We have an electronic air cleaner that is cleaned regularly, which doesn’t seem to be adequate.
Thank you in advance.
— Lawrence Klippenstein
Answer: It is always nice to hear an update on advice from a previous column. Also, using floor-vent filters may help a little in reducing dust, but the best option is to replace your electrostatic filter with high-quality disposable pleated filters, which are changed frequently. That will be a lot less effort and should work just as well, if not better.
I suspect changing the mesh size on the HRV intake-vent hood may have had some benefit in reducing or preventing frost accumulation, but the upgraded insulation may be the true saviour. If the existing fibreglass insulation, wrapped in plastic, was wet, damaged or had holes, warm air from the home may have leaked into the duct. If this warm, wet air contacts the incoming cold air, condensation is almost certain. Blowing foam insulation around the duct in that area may have helped prevent any warm-air leakage, minimizing the moist air that causes the frost.
As for installation of individual filters in floor registers for your heating system, I don’t think there would be much opposition from HVAC contractors, as long as you did not want them to install these items. There are no pre-manufactured filters that I know of and all would have to be retrofitted by cutting some form of filter material or fabric to fit each register or heating boot. During the course of regular pre-purchase inspections, I have seen some homeowners attempt this, presumably by themselves, but I don’t know if they have been effective. On the other hand, if you have a small electric air filter, which slides into a standard one-inch slot in the return-air ducting, then changing that may be the simple answer.
Most of the one-inch-thick electrostatic filters I see are not functioning properly or effectively. This could be due to poor maintenance and cleaning by the homeowners, but more likely, it is inherent in the products. Any type of furnace filter designed to be cleaned may be subject to poor performance over time, due to typical wear and tear or just a lack of attention to detail. Once dirty and plugged up, these filters may never regain their original performance. So, unplugging your unit and replacing it with a high-quality disposable pleated filter should be the simplest and least costly option. You will have to remove, discard and replace the filters every couple of months, but that may be a small cost for the improvement in dust management.
Putting individual filters on all the registers in your home will be a very time-consuming effort, at moderate cost, especially if you replace them regularly. You are probably much better off tossing out your old cleanable electrostatic filter and using regularly replaced, inexpensive pleated filters to prevent excessive dust in your home.
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 the address below. Ari can be reached at 204-291-5358 or check out his website at trainedeye.ca.