Manual J is supposed to be the gold standard, but I swear there’s always a fudge factor.
- Manual J is great in theory, but in practice? Depends who’s running the numbers and how honest they are about insulation, windows, etc.
- Short cycling in shoulder seasons is almost inevitable unless you go with multi-stage or variable speed. Single stage just can’t throttle down enough.
- HRV/ERV—totally agree. If your house isn’t sealed up like a submarine, it’s mostly just another thing to maintain. Mine’s been more hassle than help some months.
- Honestly, I wish more pros would spend time on blower door tests and less on “rules of thumb.”
Getting The Right Size Heating And Cooling System Without Losing Your Mind
Manual J is great in theory, but in practice? Depends who’s running the numbers and how honest they are about insulation, windows, etc.
This hits home. I’ve seen two different HVAC subs run Manual J on the same house and come up with almost a ton’s difference. One guy actually walked the house, checked wall thicknesses, window labels, attic depth—other just plugged in “typical” values from his truck. Guess which one was closer to reality.
Short cycling in shoulder seasons is tough to avoid with single-stage gear, yeah. Ever try pairing a smaller air handler with a bigger coil? Sometimes you can fudge it a bit for better part-load performance, though it’s not perfect. Multi-stage definitely helps but isn’t always in the budget.
Blower door tests are underrated. Surprising how many folks still don’t bother—maybe because the results can be humbling? I’ve had clients shocked at how leaky their “tight” homes are even after foam and caulk everywhere.
HRVs/ERVs...honestly unless you’re really sealed up, they’re often more trouble than they’re worth. I end up cleaning mine more than using it some months too.
- Manual J is only as good as the person doing it. If you’re not getting someone who actually inspects the house, you’re basically paying for a guess. Seen it too many times—numbers look official, but they’re just “best guesses” from a spreadsheet.
- Short cycling drives me nuts, especially in open-concept spaces. I’ve had clients complain about hot/cold spots and it’s almost always traced back to oversized units or lazy duct layouts. Multi-stage is great, but yeah, not everyone wants to pay for it.
- Blower door tests should be standard, honestly. People are shocked when I show them how much air leaks through their “sealed” homes—especially around recessed lights and outlets. It’s eye-opening.
- HRVs/ERVs... mixed feelings here. If your house isn’t super tight, they can be more hassle than help. I’ve seen people install them because “it’s what you do,” then never maintain them or just leave them off.
- My advice: push for a detailed Manual J, get the blower door test, and don’t let anyone talk you into bigger is better. Comfort beats bragging rights on tonnage every time.
