Gas and Oil Home Heating Furnaces - Air Volume Or Velocity Question

We do not get enough velocity out of our ducts the unit is 20yrs old but the duct work is 50 yrs The outside unit is 4yrs old Could the problem be due to the size of the ducts.The house is 1100 sq ft the main trunkline is 10"x24''x23' meatal and the ducts to the rooms are 7"x 16' and there are 7 of them not sure of the blower size either . This is the first season for us to run the air the air is very cold but no air volume. same as with heat. today is first time to run ac and im not to happy Going to check tomorow for leaks and things of that nature I just wanted to know if I can reduce the hole duct system to get more air or what thanks Jim

1) Check the air filter first.
2) Then inspect the indoor coil. A dirty coil will also restrict airflow.
3) Check the blower wheel vanes for dirt also.

It sounds as though you have weak air everywhere. Is the blower a belt drive? I think you are going to have to clean 20 years of dirt out of this air conditioner.

Hello Jim and Welcome to the Heating and Cooling forum and our Do-It-Yourself Web Site.

There are several possibilities for an air flow restriction.

Dirty Air Filter
Restricted Air Return---something like furniture, etc blocking the return register.
Seperated Ducting
Slow Fan Speed---could be caused by a defective and or dirty fan blower motor.
Restricted A/C Coils...restricted by years of accumulated dust etc.
Reducing the ducting size and or any part of the air flow system will not cure the problem. It will only make matters worse.

Several other resident heating and cooling professionals on this type of system, replying within this forum, could have additional helpful information, suggestions, advice. Check back on your question several times for additional replies.

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Hey thanks had not thoght of the coil being dirty and yes it is a belt drive as i said going to check all that stuff tomorow after i buy knee pads Ha Ha cant work like i used to thanks again Ill let you know how it turns out

hi sealed all ducts today, Checked blower and coil for dirt, must have been cleaned recently hardly dirty at all. Have a little more are velocity not much tho. The motor is a belt drive,can the speed of blower be increased ? Can this be done by a pulley change ( if so motor or blower pulley) or is there another terminal on the motor to increase the speed . Thanks looking forward to your advise

I would hope after 20 yrs of running, you checked the coil WITH a flashlite to see if it was plugged up deep indide the fins. Is your blower wheel also clean ? You may only need yto change the belt, since it operated ok over the years. If you change the belt, or increase motor speed with a larger motor pulley, you don't want to overload the motors' amp rating! Are all the registers and returns open, including any dampers? Your duct sizes are in the ball park for both volumne and about 800 fpm. at the trunk.