Chilly house after renovation.

We put a small addition on our house (about 10x13) We heat with forced air gas. The addition is professionally built and properly insulated. It is closed off by folding French doors with a one inch gap between the door and the floor. The furnace is in good condition and the filters are changed regularly. The heating ducts in the basement were extended and a register installed in the new room. However we notice that end of the house is noticeably cooler (68F when the thermostat is at 71F) and the new room itself is very cool when the French doors are closed. The thermostat is on the other side of the house which is fine. My suspicion is that we need an extra cold air return but I don't want to go to all that work without being sure. All input and suggestions much appreciated. ds
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We put a small addition on our house (about 10x13) We heat with forced air gas. The addition is professionally built and properly insulated. It is closed off by folding French doors with a one inch gap between the door and the floor. The furnace is in good condition and the filters are changed regularly. The heating ducts in the basement were extended and a register installed in the new room. However we notice that end of the house is noticeably cooler (68F when the thermostat is at 71F) and the new room itself is very cool when the French doors are closed. The thermostat is on the other side of the house which is fine. My suspicion is that we need an extra cold air return but I don't want to go to all that work without being sure. All input and suggestions much appreciated. ads
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A few things to investigate along with the cold air return are:
- was the forced air system rebalanced after the extension? - does the existing furnace have enough additional capacity for the new addition? - were all the joints between the foundation and wall headers properly sealed to prevent the ingress of cold outside air? - were all the window and exterior door frames (if any) sealed with an expanding foam insulation appropriate for windows and doors?
The ingress of cold outside air may also be a contributing factor along with a properly balanced forced air heating system to provide comfort in the new addition.

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My suspicion is you had a moron do the heating. Of course you need a return. If the cold air does not move out, the hot air cannot move in. You can be cheap and do a hack job, but you can't change the laws of physics. Get the contractor back to do it right. It was not professionally built as you state.
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DS wrote:

What you need is someone who really knows what they are doing to evaluate the situation and decide first if the existing heating unit can handle the additional load, and second how to properly modify the existing duct system to accommodate the changes.
They should do some measuring and several calculations before they can make a suggestion. If someone comes in and just looks around and says this or that, ask to see the Manual D they did. If they don't even know what it is, pass on that contractor. If they know what that means and try to say they don't need that or do a quick one without doing a Manual J dump them as well. The Manual D is used to compute the duct design and the Manual J the heat load. You will need both.
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Joseph Meehan

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Don't be a moron. Add a return and increase the duct size to the addition by 2 inches (7 to 9). With an adjustable vent you should be able to obtain a perfect balance between old and new.
It is NOT rocket science!
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DS wrote:

If the insulation is properly done on all dimensions, even without heating the room temp should be reasonable. Tony
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