Hello. I've been having some HVAC issues and this site has been a tremendous resource in learning about HVAC and diagnosing my problems.
Based on my observations and research, I believe I have a problem with insufficient return air ducting. (More below, for those who are curious.)
I'm looking for a good HVAC ductwork contractor near Basking Ridge, NJ who could confirm (or refute) my diagnosis, and who could propose a solution that would not involve ripping my house apart.
Thanks for your help.
P.S. If you have any thoughts or suggestions based on what I've written below, I welcome your comments.
- House built in 1981
- Forced air (two zones - upstairs/downstairs - about 1400 sq. feet per floor)
- Two new Lennox 70K BTU furnaces (94% eff) located in the basement, two older Trane condensors (XL1200?) at 2.5 tons each, Air Bear 5 inch media filters, April-aire 550 humidification systems
- Duct trunks (rectangular metal) extend the length of the basement
- Most supplies are 6 inch round metal ducts
- Most returns are joist bays, panned in the basement, which feed into the return trunks
- Finished basement, with sheetrock enclosing the trunks and a drop ceiling almost everywhere else. This has made tracing the ductwork very time-consuming...
- When it's hot, the upstairs does not cool from setback at 2-3 degrees per hour as many say should be expected. When we had 95+ degree weather a month ago, it took 8 hours to drop 6 degrees
- The upstairs AC is on a lot. The downstairs AC hardly comes on
- The upstairs has 13 supply registers and 6 return registers. Downstairs is 14 and 6, respectively. They're about 6"x10" registers.
- The upstairs rooms have positive pressure - you can feel the air "push" on the doors
- There is little to no air draw at the upstairs return registers, especially in the rooms furthest from the air handlers.
- There is strong air pressure at the 1st floor door leading down to the basement - the air is pushing its way into the basement
- The panned returns are leaky. For the ones I can reach, I've started sealing the gaps with mastic, fiberglass tape, and foil tape
- The return duct (plenum?) leading into the air filter measures 7"x25". The opening at the filter is large - 20"x25" I think. At its narrowest, just above the coils, the supply plenum(?) measures about 19"x19".
- The upstairs return trunk narrows to about 8"x17" just a few feet away from the air handler. (This is from memory.) It's visibly smaller than the downstairs return trunk. It's also smaller than the upstairs supply trunk.
- The Air Bear 5 inch media filters are a little dirty. But I had all these air flow issues even when they were new. (And also when I had 1" Filtrete filters with the prior system.)
- When the basement was finished, the contractor cut holes in each of the four trunks and installed supply and return registers in them. Thus, the finished basement is served by both of the systems.
- I don't know my static pressure.
- I believe the furnace, AC and blower sizings are appropriate for the load.
- The refrigerant pressure in the ACs tested OK in April 2008.
- It's clear the preferred return path for the upstairs air is into the upstairs hall, down the stairs, and then down the basement stairs.
1) Insufficient return registers
2) Leaky return ducts (panned bays)
3) Insufficient return ductwork sizing
I'm sure #1 and #2 are contributing to the problem, but I think #3 is the real issue. This is why I need a contractor - how do address this issue, and how much will it cost?