Are Duct Booster Fans Crazy? Or will they solve insufficient cooling air reaching 2nd floor?
2nd floor of my Kansas City 24yo home (bought 3 years ago) is consistently 6-12 degrees (F) warmer in summer than first floor. The problem I noticed from Day 1 is simply that the 2nd floor does not get enough air from the HVAC system. With the house fan on full blast, you can barely feel any air coming up through the floor registers in the bedrooms, while the registers downstairs are blasting out cold air.
Supposedly, a duct booster fan isn’t a good idea. However, after everything else I’ve tried that is supposed to address the problem, I think a duct booster fan is by far the least expensive and most effective solution that would directly address the problem. In fact, I’m coming to the point where I think everything else is stupid.
So if there’s a reason that I may be delusional, please convince me otherwise. But this is my throwdown challenging the “conventional wisdom” of building science on this one.
Here’s the situation as it stands:
A. All the ducts are inaccessible. Don’t tell me it’s a duct/supply sizing problem. Of course it is. I’m not going to spend $$$$ tearing apart the house to let an incompetent contractor try to fix what the original inept contractors did, if a <$200 solution will fix my problem. B. Supply trunk line to 3 bedrooms on the 2nd floor is smaller than to the 1st floor, and has a much longer run, with more bends, and crosses over the unconditioned garage. So a long, hard push for cold air to get to the hottest rooms; instead, the air follows the path of least resistance to rush out of the easy, short, huge trunk path of the 1st floor. C. Professional air sealing performed, R49 attic insulation (though I’m convinced insulation is a very minor factor for cooling concerns), solar attic ventilation fan. New low-e double glazed tinted argon windows. AC recently repaired (kink in coolant line, leveled, cleaned, recharged). Added a return vent in finished portion of basement. Old PSC blower, but still seems to function well. My potential solutions: 1. Install a duct booster fan (with pressure switch or linked to main blower) on the vertical rise of the trunk line that supplies the upstairs rooms — should pull more air upstairs and give it the extra push it needs to overcome the distance, rise to the second floor, bends, and undersized ducts and still throw the air into the rooms to mix well. 2. Install manual dampers in the trunk lines and adjust seasonally — best done in conjunction with the duct booster, to restrict 1st floor airflow that steals the lion’s share right now. Duct booster may correct the air pressure problem of cutting off the majority of the vents via the damper. 3. Use AeroSeal to seal duct leaks internally throughout the system and try to reduce loss of cold air and increase flow (at likely >$1,000 for a 10 year life, not sure this is worth it, or if it even works as marketed).
4. Install EcoBee or similar thermostat with multiple sensors to average out set temperature vs. actual with upstairs — problem is, without correcting supply, this will just freeze out the 1st floor while it tries futilely to bring down the 2nd floor temp (already keep 1st floor thermostat at a cold 72/70 at night just to try to keep the upstairs from getting too hot).
5. Replace old PSC blower with Evergreen ECM — still must overcome the draw of the 1st floor trunk line, and if it runs in lower speeds, will likely only exacerbate the problem of not pushing sufficient air upstairs, UNLESS combined with 1-4 above
6. Install a heavy curtain across stairwell to slow cold air spillage downstairs and hot air rising (the powerful chimney effect going on here); works for my in-laws in their split level, holding heat in at the lower level, not sure how well it will work to keep cold air in, particularly if we’re just not getting enough cold air up there in the first place
7. Complete redo of HVAC system (too expensive):
a. Access, resize ducts per Manual D, seal and insulate (but still have the same problem of long runs, bends, and vertical height to overcome);
b. Replace single stage AC with higher efficiency dual stage (same air flow problems at low speeds, however);
c. Add automatic zones (expensive, difficult to access ducts, still may have pressure problems, but perhaps an automatic system would be able to detect and correct, signaling the blower to blow harder for the upstairs zones when those zones are active)
d. OR Add a second heat pump unit dedicated for the upstairs — would have to figure out how to get an air handler access to the trunk lines and separate it from the garage
e. OR Add a ductless minisplit system for the upstairs — expensive, poor room-to-room balance of air, unlikely to extract sufficient moisture from air
I think 1 and 2 are my best bet by far, followed up by 4 and 6 as cheap options, and possibly 3 and 5. If I thought I could easily dedicate a new heat pump to take over the upstairs supply lines per 7d above, I’d probably do that, but new air handler in the garage = bad idea, and probably against code, so I’d need to enclose and finish a new mechanical room to code and probably reroute/do significant duct work.
So, why SHOULDN’T I install a duct booster and manual dampers?
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