We read your articles every weekend in the Free Press home section and may I say that they are very informative and resolving.
My wife and I continuously discuss whether it is best to leave the furnace fan running all day so that it keeps circulating the air in the house, keeps the warm air moving, draws the cold air from the basement etc. Why would we do this if we also have a Heat Recovery unit installed in the house? Your thoughts?
The practice or running a furnace fan on continuous operation is a good one to help circulate the air in a home and help provide more even heat distribution. This may work directly in conjunction with your Heat Recovery Ventilator (HRV) and I will explain this further.
Ideally, if all homes were a simple square box without any dividing walls or furniture, heating and cooling would be a simple matter. Because our homes have several rooms, with varying uses, sizes and configurations, even heat distribution and air movement is a challenge. One way to help prevent cold spots or areas of little air movement and moisture build-up is to attempt to have the air in the home constantly moving. If the air is constantly circulating, it will help dry areas of condensation that may form on windows or basement storage areas prone to poor airflow. If the air only moves when the thermostat calls for heat and the fan engages, there is more chance of damp, musty areas developing in hard to reach areas in the home.
The majority of modern furnaces have a 2-speed or variable speed fan motor that can be set for low pressure air circulation continuously. Most newer thermostats also have a switch to turn this fan on and off at will. Setting this fan switch to the on position should engage the furnace fan to the low mode, which will move the air through the ducting at a moderate rate. Once heat is required, and the thermostat calls for the furnace to fire, the fan will automatically move to full speed and the heated air will move across the heat exchanger and through the ducts with greater velocity.
A Heat Recovery Ventilator is a mechanical ventilation system that is designed to expel stale house air and replace it with fresh air from the exterior, without significant heat loss. This is done with a small heat recovery unit inside the mechanical box. The main purpose of this ventilation system is to reduce the humidity in the home by bringing in cool, dry outside air to replace the heated, humid air that is created by normal household activities in the heating season. The short answer to your question is that the furnace fan running on continuous should only serve to improve the performance of the HRV.
Most HRV’s are installed with flexible ducting that is connected to the metal ducting in the home’s heating system. Also, they are typically wired to the furnace controls, as well as their own, so that the unit will be powered up once the furnace fan engages and vice versa. In this way, the house fan helps to circulate the air in the home when the HRV turns on. This provides much increased airflow to the HRV and allows better operation and dehumidification. The HRV’s have small fans and ducting which cannot handle the volume of air in an average or larger sized home, on their own.
If you run your furnace fan on low speed continuously, it should only serve to increase the airflow to the HRV and provide a very regular rate of air exchange in the home. This may significantly limit the number of cycles that the HRV will go through from its own Humidistat controls, but that should be of no consequence. The goal of improved indoor air quality with minimal heat loss should be closer with this scenario.
There may be a couple of small drawbacks to this method of continuous fan usage. Firstly, the furnace air filters and the HRV filters and components will have to be changed or cleaned on a more regular basis, due to the increased air movement across their surfaces. Fortunately, this should help reduce the dust and airborne particles and further improve air quality. This may be especially beneficial for home occupants with allergies or with pets in the home. The second drawback, which may be your wife’s concern, is the feeling of cool air emanating from the heat registers. This can feel cool to the skin, as the air is not heated continuously and will be circulating at room temperature rather that at the familiar warm temperature we associate with central heat.
Regardless, the few small negative aspects of continuous fan usage should be significantly outweighed by the advantages. One thing to keep in mind is that HRV’s will only run at optimal performance if they are regularly cleaned and balanced. Balancing the amount of air incoming and outgoing from the unit is important to proper operation and should be done on an annual basis. This servicing and balancing can be done by most licensed heating technicians, often at the same time as annual furnace service.