Older ducts may not move air efficiently
Q. This summer we had trouble cooling our second-floor bedrooms. I had a window unit installed, but it takes away from the charm of my older home. However, I can remove it in the winter. I tried opening the vent on the side of the furnace hoping to draw some of the cooler air from the basement, but that didn’t help. Do you have any insight into this problem?
A. Moving cold air from the basement to the upper floors has always presented a problem for homeowners and installers. Cold air is more dense or heavier than warm air, because when the air is heated, the atoms move farther apart, so warm air is thinner. Cold air is compact and cannot hold as much moisture as warmer air. As the basement’s furnace fan attempts to force cold air to the top floors, the air will gain heat as it travels through the restrictions of the ductwork, so the air coming from the higher-floor registers will be warmer and contain more moisture molecules.
Adding dampers to the supply ducts would allow you to choose which floors receive the majority of the air from the fan, but opening a cold-air return right next to the fan may not be a good idea. If the basement door is closed, the fan will pull air from every opening in the basement including sump pits, laundry and floor drains and could increase the amount of radon gas buildup in the home. For more information, visit www.epa.gov/radon/.
Before adding a second air-conditioning unit, have the ductwork inspected by a trained and qualified HVAC (heating/venting/air-conditioning) expert. Note I did not say “technician,” because the sizing and installation of the ductwork requires a great deal of technical knowledge and design work using manual-D calculations published by the Air Conditioning Contractors of America.
With some states adopting new energy codes, and with Energy Star 3.0, all new HVAC installations must be installed using manual D for the ductwork and manual J to size the equipment.
In older homes, the ductwork will likely be undersized and will have major air leaks at joints and seams.
If you have flexible ducts in the attic or basement that carry the air to the register, the corrugation inside the pipes will restrict airflow and bends such as 90-degree elbows further restrict airflow. Air restrictions inside the ducts heat the air and overwork the fan and air conditioner.
If the vertical ductwork is accessible, it would be energy-wise to have it replaced. Even if some wallboard inside the home has to be removed to access the ducts, the value of energy savings and the comfort levels you will experience would be to your advantage.
Ÿ Dwight Barnett is a certified master inspector with the American Society of Home Inspectors. Write to him with home improvement questions at d.Barnett@insightbb.com.
Scripps Howard News Service