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Here's How: Have the Ductwork Properly Sized for Your House

James Dulley on

Dear James: The bedrooms on the north side of our house are always chilly. We are planning a new house now. What causes this and what should we do to avoid the same problem in our new house? It will be two stories. -- Ron H.

Dear Ron: There are several possible causes of the chilly conditions in these bedrooms. They are on the northern side of your house, which exposes them to the coldest winter winds typically from the northwest. Also, the wintertime exposure to the sun is minimal on the north side.

It sounds as though the heating duct system may not have been designed properly. Since two northern rooms will have great heat loss and will need more heat to stay warm, the ducts from the furnace should have been sized accordingly.

There may be just one main duct leading to those two rooms. Inspect this duct near the furnace for a small handle. This will be the handle of a duct damper. If you are lucky, it may have just gotten turned, which blocks some of the heated air going into the duct. Usually the fully opened damper position is when the handle is parallel to the duct.

To avoid this problem in your new house, make sure the general contractor hires a competent HVAC (heating, ventilation, air conditioning) contractor. The HVAC contractor, considering the building plans, insulation levels, windows, etc., can determine how much heat each room will need during the winter.

These calculations for the rooms will allow the contractor to determine the overall heating capacity required from the furnace and the size of the ducts leading to each room. There can be a significant variation among the heating requirements for different rooms in a house.

You may hear them talking about "static pressure". This refers to the resistance to the heated air flow in a duct. A duct that is long with many bends, such as one leading to a second-story bedroom, will create a lot of resistance to air flow. Air, like water, will naturally follow the path of least resistance, so more of it will flow out into another room.

Talk this over with the HVAC contractor to let him know you are knowledgeable about this. Ask to see his computer printout of the recommended duct sizes. You may see quite a range of different duct sizes, particularly in the main branch ducts. Also, make sure duct dampers are installed in the ducts so you can fine tune (balance) the system.

Instead of installing just one large furnace for the entire house, you might consider installing two smaller ones with two separate duct systems. This is commonly done in many parts of the country. The smaller furnace for the second-floor runs only when the bedrooms need heat and the hot air cannot blow out into another room on the first floor instead.

Your final option for your new house is to install a zoning system with motorized dampers built into the ducts. With several wall thermostats mounted throughout your house, they tell the dampers which rooms need more heat. The system responds by closing dampers to room which are already warm enough. This forces more heated air to the chilly room. It works in reverse with your central air conditioner during the summer.


Send your questions to Here's How, 6906 Royalgreen Dr., Cincinnati, OH 45244 or visit To find out more about James Dulley and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at

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