Half the vents in my house have poor air flow. How can I DIY and fix?

Look for ''balancing valves'' which will be found near the air handler. These have the appeance of small handles attached to the side of the ductwork. They control flow to the vents they feed, & allow u ''balance'' flow from one place.

Since u DO have strong flow from some vents, the problem is not the air handler itself. If no balalncing valves r found, best thing (only thing, really) is to close or partially close vents in strong flow areas, which will force more air into the sluggish areas.

partially close the vents going to the basement,you don''t need them open all the way due to basement is cool in summer,and open the upstairs or first floor all the way its called air distribution.

You have a lot of variables here. There may be something blocking a portion of the ductwork. There may be dampers closed or opened that should be otherwise. There may be issues about how far one part of the house is from the source. Since u have access to the basement, go down & trace the ductwork. Take a magic marker & mark the vents that do not seem to produce much air flow. Do they all seem to be on the same trunk (branch line) of the ductwork? If so, check the point where this line branches off the main & ten out to the first bad duct. There could be anything in there from that pair of undies u lost last year to Jimmy Hoffa is corpse. (Are u missing any pets?) No obstruction? Try closing the vents or the dampers supplying the vents that produce lots of air flow. Does the flow improve in the bad areas? If so, it is just a balancing issue. This is most likely since the problem started after someone took everything apart & cleaned.

booster fans suk! they r junk unless u spend $$ to get good ones.. get ur camera out & look down into the vents.. make sure they didnt come disconnected. also sounds like system is out of balance.. also there might be dampers down near the furnace that have been moved.. its also the way u balance it.. vents that exit closest to the furnace should be turned down (cut flow) if u have dampers look near the furnace for small levers on the ductwork.. if u look close enough u will see a flat end.. that flat end is in line with the damper. if the 2 rooms r sharing a vent.. close hers some

close the vents to rooms u do not go into often & close the doors (laundry room for example). My thermostat upstairs is in the master bedroom. Usually my room cools before my sons rooms at the other end of the house & the A/C shuts off. I kept toying with the vents in my room until there rooms were cool like mine. Now that side of the house is pretty close to the same temperature as my bedroom at all times.
It sounds like whomever ran the ducts for the basement tapped into the same A/C ducts that were only meant for the main floor. A/C units r listed as tons. I have a 1700 square foot rental that I just installed a unit into. It was a 3 ton unit but I increased it to 3.5 tons. Either close all the vents to the basement or get a separate unit for each floor.

Good Luck

I am not a home heating/air professional by any means, but, here is what I've done in my home. My livingroom vents r farthest from the furnace & that is where the thermostat is located. I got the same results as yours in my livingroom. My system has ''dampers'' in the air supply pipes. I closed them to 3/4 shut in the rooms closest to the furnace. Two of them I closed completely (still get enough cold air as damper is not 100%)The ones to the livingroom I removed completely. This allows more airflow to the room.
Also: I know there r fans that can be installed in the weak lines that will push more air into these areas. They r activated by the thermostat along with the furnace.
Hope this helps!

There r ''booster fans'' that u can get at home depot & lowes, or at least they can tell u who to go to, unfortunatly u have to wire them up. I had them in all the rooms of my last place & it was nice because every room was the same temp due to increased circulation. Also ensuring u have clean filters is a good simple thing. When u change ur filter, see if there is dirt & dust behind it, if there is, u may want to have ur vents cleaned, which is honestly best left to professionals.

make sure pipes are tightly sealed and vents are in good condition.make sure stuff is clean and free from debris