Many homeowners find that they have hot and cold spots or rooms within their homes, when heating and/or air conditioning with forced air furnaces, as shown in Figure 1.
Figure 1 - Forced air furnace
The basic problem, providing the furnace was originally designed to provide adequate heating or cooling of the home, is air circulation. Poor air circulation, especially in older homes is not uncommon.
Causes Of Poor Air Circulation:
- One of the simplest causes of poor air circulation is a clogged air filter. Furnace air filters need to be changed regularly, at least every three months. If you are using one of the more modern furnace air filters that remove a lot more dirt and dust out of the air, they will clog faster and hence, will need cleaning or replacement much more often.
- In order for a forced air furnace to work properly it is necessary that the amount of air leaving the registers is returned in the same quantity as the air going into the furnace - the cold air return.
- As children become older, it is not uncommon that bedroom doors remain closed for most of the day. Generally a cold air return is not placed in each bedroom and with the addition of wall to wall carpeting, a closed door seals the air inside the room, preventing it from exiting the room and finding the cold air return duct.
Cold air returns are usually placed in a central location in the home, such as a common hallway. Over the years people renovate and modify their homes to a point where the cold air return is no longer in a location that can exhaust air from all the rooms evenly. Walls and doors are added and walls are removed without any though or adjustment to the cold air returns in the home.
If the cold air cannot exit the room via a cold air return, the air will not be circulated within the room and hence, the room will be colder than other areas of the home.
- Changing windows and doors and/or installing excessive amounts of weather stripping can change the air flow in a home. Older windows and doors may have provided an exit for the air within a room or an intake path into the furnace of return air.
Figure 2 - Wrapping an air duct with aluminum foil tape
- Duct work, will over time, leak more air than it did when originally installed. Older duct work was not sealed well at joints and continuous vibration will create loose joints. Adding aluminum foil duct tape> (not the grey tape that you buy at your local big box retailer) to the joints, will keep the air within the ducts, where it belongs, as shown in Figure 2.
- Thermostat location can also have an impact on proper heating and cooling. Thermostats should be mounted on interior walls away from any drafts or sudden changes in temperature due to the opening of windows or doors. Heat generated by kitchen appliances or fireplaces in relatively close proximity to the thermostat can also upset its value as a home temperature controller,
Sealing the duct joints will also provide energy savings, as escaping air does not heat of cool a home properly.
Before you run out and invest in a new furnace it may be beneficial to have the HVAC system inspected to see if a minor investment in some duct repair and/or modification may solve your problems. A new furnace with old air ducts will probably not solve the problem of cold and hot spots throughout your home.