Is Following Manual D Expensive?
Builder here. Heard something today I had not heard before from an HVAC contractor and soliciting feedback from all.
My HVAC contractor told me that following the process of a Manual D resulted in duct work that was expensive. It seemed from what he said he was implying material costs, but in this tight labor market, I could assume that meant labor costs as well.
I’ve never performed a Manual D myself, but have worked with other contractors that I know did do them. I’ve not noticed anything cheap or otherwise appearing different/cost-effective about the duct work with this contractor than those other contractors
Apart from comments along the lines of, “not doing it right is always more expensive” – is there any basis in this statement, or is he just not doing the Manual D correctly?
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Replies
It may be expensive compared to the default installation standard, which is to do whatever in the field to make it fit with flex. The cost differential between how he fabs/installs now vs fab/install per Manual D is probably directly related to how poorly / far from Manual D standards he currently fabs/installs....
Thank you for the reply. Actually, flex is rarely used in our homes, only in cases where a jump outside the envelope is required, and that's avoided if at all possible. Tons of sheet metal and long runs are common. That's why this answer surprised me - I don't know how it could get more expensive, unless it required larger profiles.
Following a Manual D design will often suggest using less common sizes of ductwork. There is a bit of a price (as well as availability) difference between these less common sizes and those most frequently manufactured - especially for fittings. It also means the installer needs to carry a larger inventory with them for dealing with unexpected on-site challenges. When we did our ductwork, we had to special-order a number of fittings that weren't available from the local suppliers.
That said, the Manual D recommendation is the minimum size for the necessary delivery. You can always upsize the ductwork to the next more standard size, and use dampers to adjust flow back to balance (though it our service area, very few installers bother to balance ductwork).