Question: Could you please advise on the following dilemma? I have a Keeprite high efficiency furnace and a heat recovery ventilator (HRV) installed in my home, built in 2014. The HRV is connected to the furnace and both have a separate control. When I turn the HRV on, via its control, the furnace fan starts running at the maximum possible speed. The furnace motor speed is extremely high, blowing the air very strongly. The HRV runs only when it is turned on, not constantly.
My concern is that this high furnace fan speed affects the furnace motor. I’ve changed the motor because the previous one died after three years of seasonal operation. I suspect that this HRV operation, which triggers such a high speed, was a contributing factor.
Thank you in advance, Henry.
Answer: Sometimes when an element of a home system fails there is no direct connection between its demise and other connected systems, even though it appears there might be. The furnace blower should be connected to the HRV control and should run at high speed when engaged, to help it effectively operate.
Some of the most common questions I receive are related to proper use and set-up of heat recovery ventilators (HRV). Especially since these have become a mandatory part of new homes in our area, in the last decade, inquiries are frequent. These fairly simple mechanical devices are often misunderstood, mainly because homeowners are not shown how to properly operate the system. Sometimes they are also not properly installed, or more commonly have the controls not fully engaged. In those situations, a regular service call by an experienced HVAC technician normally solves the problem. In your home, it appears that the HRV is properly set-up, and may have nothing to do with the short life of the furnace blower motor.
The reason that the HRV is cross-connected to the furnace blower control is to help move air through the entire home, once the HRV turns on. This is beneficial because that ventilation system has limited ducting and only a few intake registers in the entire home. There should be an intake in each bathroom, one near the kitchen, and often one in the laundry room. That is much different than the fresh air intake registers for the furnace, which has at least one register in each room of the house.
The HRV should have one duct that is connected to, or in very close proximity of, an opening in the furnace return air plenum. In this way, some of the air circulating through this small box will mix with the house air moving through the heating system. Even without the furnace blower running, this could help air distribution. The problem is that the HRV blower is very small, in comparison to the furnace fan, so it is not capable of efficiently circulating all that air by itself. Once the furnace blower engages, it will easily make up the shortfall and help the ventilation system move the conditioned air through the entire house. That will prevent the HRV from running too long, which can cause it too frost up in very cold weather.
It is also proper that the furnace blower run at maximum speed when the HRV engages it, due to the relatively cool temperature of the air being moved. The warmer the air the easier it is to blow through ducts. Because the HRV exhaust air is mixing with the incoming outside air it can be fairly cold when it enters its components.
A modern high-efficiency furnace is designed to have a blower that will last the entire life of the unit, with minimal maintenance and lubrication. It is designed to run almost continuously on the coldest or hottest days of the year. As long as it is cleaned and serviced regularly, it should not become deteriorated for more than two decades. The only thing that may prevent this longevity is infrequent replacement of the furnace filters. If left in too long they can become so dirty that airflow through is severely impeded, so change them as required.
Having your HRV control engage the furnace blower when it comes on is a proper set-up and should not affect the longevity of the motor. Your original one probably had a premature death because it was a defective or poorly made unit, not because the HRV caused it to work too hard.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and a Registered Home Inspector (RHI)(cahpi.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.