I have a 28" x 16" x 6" deep AprilAire 2400 on my (ridiculously oversized) 5 ton system that's pushing ~1800cfm. It's possible to get media as tight as MERV 17 that fits, but I'm usually running MERV 11 to MERV 13. I haven't measured the static drop across the filter in recent memory, but IIRC it was low enough that it was the least of my concerns. Even with MERV 13 filter media it's moving enough air that the AC coil never ices up. The replacement filters are a few 10s of dollars, but I only replace them every 12-18 months.
I really like this idea but can this type of filter work in my existing furnace or does it require some type of air purifier? I see there's some sort of a frame kit but I'm not clear on what exactly that's for.
That's right. The 0.8" spec should be considered an upper bound from a system design. If it's anywhere near that high when the filters are clean it's going to go over 1" if the filters get ignored it can easily go over 1.0", with ever decreasing flow.
I've got a handheld manometer that I use to check pressure differential across the filter and I'm wondering if you have a favorite inexpensive mechanical one that I could mount on each of the units so I can see pressure when I walk by? This would also be handy to use initially after whatever changes are made to the system to monitor the system pressure drop under various conditions to be sure something stupid wasn't done. Anyway, one that is mounted seems like a good idea. I see Dwyer makes both a metal type of gage and the plastic type with the red fluid. Both seem pretty reasonably priced.
Zoning has zero effect on Manual-J, which only calculates the load. Manual-S is used for selecting the equipment (and where the cfm requirements get spit out, based on the calculated heat & coolth requirements from Manual-J. Ducts are supposed to be designed using Manual-D to guarantee that the requisite cfms can be delivered to each room.
There is a lot of judgement calls when selecting equipment and designing ducts, and the design tools are just that- tools for the designers to use. Tools have become better, but they're not idiot proof. (Even if they were, the more idiot proof you make things the more creative the idiots become.) Some designers are clearly better than others, and most systems work well enough that most clients don't complain (clearly not the case here.)
Many times the ducts can be hacked in using crude rules of thumb (not Manual S & D) , then tweaked into reasonable balance using balancing vanes when commissioning the system. The success rate of rule of thumb methods is far from perfect.
Ok so I think what you're saying is that whether a separate zone is necessary as with my bedroom 3 is a judgment call? It seems to me the Manual J is a rate of flow but says nothing about how long or often that flow needs to run in a given space. I gather the assumption in a given manual J is that the design conditions of the various room are close enough to be be controlled by a single thermostat. I can't recall if I mentioned the ASHRAE FAQ I came across that sort of discusses this and makes it pretty clear at least when a separate zone is necessary. Here is the specific answer and a link to to the FAQ page if you want to look at the rest of the document.
"Areas or rooms having dissimilar load characteristics or different conditions should be controlled individually."
https://www.ashrae.org/File Library/Technical Resources/Technical FAQs/TC-02.01-FAQ-54.pdf
Thanks again for this information as it's all very helpful. I am told that I should be hearing something back from the builder today so we'll see what happens. This has been going on so long I know better than to get my hopes up.