Question: My house was retrofitted with a heat recover ventilator (HRV) system a number of years ago. Both of the home’s bathrooms had ductwork retrofitted at the time to connect to the HRV system.
The two bathrooms also have ceiling exhaust fans, vented to the outdoors, that were original to the house. The fans are still in place and functional, but have not been used since the HRV retrofit. From time to time, especially in winter, the air in the bathrooms is noticeably cooler than the rest of the house, as well as having a fresh air scent, as if a window has been opened. There are no windows in either bathroom. The cool air in the bathrooms doesn’t seem to be related to whether or not the HRV is running.
Is it possible that the existence of the ceiling exhaust fans has put the HRV out of balance, resulting in outdoor air being drawn into the bathrooms? Would it be advisable to remove the ceiling exhaust fans and their ductwork entirely? — Allan, West St. Paul.
Answer: Periodic balancing of your HRV is a very good idea, to maintain proper operation, but keeping the older ceiling fans in place may be a more likely cause of the cold air intrusion in your bathrooms. Removing and/or sealing these may help warm the cooler rooms, but regular cleaning, servicing, and balancing or your HRV should be done, regardless.
There may be several factors that are causing your bathrooms to be colder than other rooms in your home. These may include location of the rooms, proximity to the furnace, uneven attic insulation and ventilation, or an improperly functioning HRV. The first item to address, which is quite normal, is that bathrooms do not typically have return air registers or ducts installed. Because these are not present, airflow may be more restricted than other rooms, especially when the door is closed. Because the warm air coming from the heat register does not have a direct path back to the furnace, warm air circulation may not be as good as elsewhere.
Also, most bathrooms have at least one exterior wall, which may be on the north or west side of your home. These are the walls that are typically the coldest, due to the lack of direct heat from the sun, and the prevailing cold winter winds. These two factors combined could make the bathrooms colder than others, even without any of the other variables taken into consideration.
The possibility of the ventilation system being imbalanced may be a factor in colder bathrooms, but other malfunctioning components of that system may also be to blame. Especially with retro-fit units, I often see controls that are improperly used or not proper set up correctly.
In my opinion, the HRV controls should only be used by setting the dehumidistat for a desired relative humidity (RH), and manually when a shower or bath is taken.
The manual controls in the bathroom should be simple, with the HRV turned on by a simple finger touch. These may be automatically set to run for a specific length of time, or have optional timed buttons to select.
The main control, often installed beside the thermostat for the furnace, should have a functioning dial or touch control with variable settings based on RH. These should typically be set around 30 per cent at normal room temperatures, for a typical Manitoba winter. When the RH in the home exceeds this setting, the unit should run until the humidity drops below your chosen level.
Many HRV systems have controls with multiple options, especially newer models. These include timed cycles such as 20 minutes on and 40 off. They may also have several speeds and an option for continuous ventilation. If these are overused your home may be come too dry, or other problems can occur, like uneven room temperatures. If your system is not well balanced, and the HRV is running too often due to a timed setting, the interior of the home could become depressurized.
This can cause cold air to be drawn in through small openings in the building enclosure. The solution to any of these issues is to call a heating, ventilation, and air conditioning technician, who has lots of experience with your particular brand of HRV. They should measure and balance the system, as well as ensuring the dehumidistat on the main control is working3.Once completed, try setting the control around 30 per cent, plus or minus five per cent, and see if the bathrooms warm to your satisfaction.
If the HRV servicing and resetting does make any difference in bathroom comfort, then dealing with the older ceiling fans is warranted. These units became redundant as soon as you had your HRV installed. Because of this, sealing or removing them should not affect anything significant in the indoor air quality in your home. Because these units have not been in use for some time, there could be some damage to the components, which is letting cold air infiltrate your bathrooms.
The first suspect would be the vent hoods, which typically are mounted on the roof or the exterior wall near the bathroom. These have dampers which function to keep cold air from entering the ducts when the units are not blowing air out. These can easily become damaged, warped, or dislodged, which would certainly allow cold air intrusion.
The ultimate solution to this potential problem is to remove the hoods, ducts, and fan housings and properly seal and patch the openings in the ceilings and the roof or exterior walls.
An improperly set up or operated HRV could certainly cause a negative pressure inside your home that would make the bathrooms feel cold and drafty, but abandoned ceiling fans may be a more likely cause, especially if the vent hoods or dampers are damaged. Proper HRV servicing and settings, combined with removal and air sealing of the old fan components should ensure your bathrooms are as comfortable as possible.
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.