Jim Wheeler: Why is that room uncomfortable?
Almost every house has one — the uncomfortable, stuffy room that usually is too warm and uncomfortable.
There are several causes for this. Usually, the main source of the problem is poor layout, design and installation. However, changing solar and seasonal loads also are important factors.
Unfortunately, especially when it comes to new homes, the HVAC contractor on the project usually gets the job by being the lowest bidder, so cost-cutting often is considered essential in making a profit.
Typically, an important part of the residential system where cuts are made is done by minimizing the ductwork and then failing to balance the airflow to each room after the system is installed. As a result, I have been in luxury new homes where the air noise is quite noticeable, the rooms are drafty and some rooms are very uncomfortable. A well-designed and -installed central system shouldn’t be noisy; the occupants shouldn’t feel drafts and all the rooms should be comfortable.
The problem with most residential new-construction systems is there usually is no plan to balance the airflow into each room because nothing was put into the budget to install balance dampers in the ductwork or to have anyone adjust them after the installation.
So, the balancing often is left to the homeowner or a service tech who must partially close discharge grilles in cooler rooms to force air into the warmer rooms. And, unfortunately, partially closing the discharge grilles is the poorest option since that creates the most noise and it changes the airflow distribution pattern into the room. Also, on a marginal duct design, closing off too many dampers can cause the system to freeze up (Yep, ice cubes!).
The common myth that many residential HVAC contractors design around is the belief proper air balancing is accomplished through a good choice of duct sizes, which isn’t true. That helps, but not many residential duct installations are really sized with complete consideration given to duct length and the losses through bends, twists and curves (especially when flex duct is used).
Of course, the other almost unsolvable problem that causes room discomfort is the changes in solar load on each room as the sun travels from sunrise to sunset. Also, there are differing needs between hot and cold weather and day and night temperatures. For example, if you plan to send extra air into a south-facing room to cool it in the summer, that puts more heat into the same room on a sunny day during the winter. And satisfying daytime cooling needs in a south-facing room might make it too cold during the night.
Are there solutions to these problems? Well, proper design and balancing are an important part of the job. However, new technology can be employed (at a higher cost) to make any room more comfortable. By installing electronic dampers in the ductwork, contractors can give each room its own temperature control.
Until now, that usually involved a lot of low-voltage wiring. Yet, recently I received a brochure from one company (HiberSense.com) that now provides wireless dampers for discharge grilles (as well as the controlling electronics) so each room can have its own temperature control. Therefore, with new technology it is becoming much easier to end the problem of uncomfortable rooms.