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I wouldn't worry.

There shouldn't be a gap between drywall and vent boot. Attic air,insulation and dirt will come in through gaps. The boots are supposed to fit cutouts but all you can do now is fill gaps with foam.

If the supply air vents fit tightly into the ductwork, you're not losing conditioned air.

However, the return (first photo) is pulling in air from inside the walls as well as from the rooms. So seal that as suggested.

Sealing might help a bit with reducing sound transfer. But don't expect much of an improvement.

Where do you live? California and some other states require that air duct systems have leakage less that a specified amount. Those gaps would not meet that requirement and the builder should correct that..

I would doubt that there would be any gaps in a party wall/ceiling, or something went terribly wrong with inspections, so there's probably much more to the story about hearing your neighbors. The workmanship of those 2 close-up pictures of the sheetmetal looks suspect though. More information would be needed to understand the what and where to offer pertinent advice. If something is to be done, it does not look like foaming the heck out of those gaps will be successful.

This is easily addressed. Buy some mastic backed tape and run strips along the perimeter of the opening, one side on the sheet metal, the other side on the wall. This will effectively seal the gaps.

I think such gaps are typical with hastily done work.. An energy rater who used to be active on this site provided the simple instructions and photos of how to do this. I don't have the photos handy but I used her suggestion to do this very thing at my house. It did make a difference.

Ahah! I found a thread and the photo it contained:

A big Shout-out to energy rater la (houzz.com)

I miss Energy Rater, truly a well of knowledge.

"California and some other states require that air duct systems have leakage less that a specified amount. Those gaps would not meet that requirement and the builder should correct that." I respectfully disagree. Ductwork is typically leak tested by sealing off supplies and returns and pressure testing. The test measures leakage at duct seams and seals. Void spaces between the exterior of ducts and ceiling, wall or floor penetrations won't affect the measured duct leakage. They will, however, permit either conditioned air to flow into unconditioned spaces or unconditioned air to flow into conditioned spaces so they should be sealed with foam sealant to minimize the consequences of the air movement.

I'm not sure your description is accurate, please tell me where my understanding is in error.

My ducts were tested as you described - thick plastic sheets were taped over all supply duct, leaving no gaps in the tape along the perimeters. A duct running to an air pump pressurizing machine was sealed against the return grill.

Consider one system with one well sealed return and one supply. Supply #1 is 4x8 and has a 1/4 inch gap between the boot and the wall all around = 4x8x 1/4 equals an 8 square inch opening. Take a second system, seal the gap but cut an 8 square inch opening in the metal duct where it passes through the crawlspace.

I believe each system will show the same air leakage when pressurized.

HI, Elmer,

The point of leakage testing is to verify that the application of mastic and/or tape has adequately sealed the duct seams and joints to minimize leakage. To that end, your return grill should have been removed and the test connection taped to the actual metal duct work. Leakage around the perimeter of ducts at penetrations is not the same as duct leakage. It would be detected via a blower door test of the building envelope using a smoke pencil to detect specific leaks. Here in Virginiaboth blower door testing and duct leakage testing are required for all new construction. The voids should be sealed as described above to prevent the above transfer of air to/from conditioned spaces.

That's not how my Cal building code-prescribed independent HERS testing was done, which was submitted to and accepted by the municipal code enforcers and confirmed with an onsite inspection. There was no blower door testing. It was strictly duct leakage, not envelope tightness.

Whatever was done in Va isn't particularly relevant to what I was describing from my own experiences, in two different Cal jurisdictions and locations.

Hi, Elmer,

The point of duct leakage testing is to prove that the leakage rate is within an acceptable limit. If the evaluator takes a shortcut, but the test nevertheless reveals an acceptable leakage rate, it passes; the "true" leakage rate becomes academic. In my area, duct leakage testing is performed in new construction to verify the leakage rate is less than 4 cfm/100 sq. ft. of conditioned floor air which is the code requirement. Blower door testing of the structure is performed to verify that the air leakage rate is less than 5 air changes/hour (ACH) at 50 Pa.

The sealing between duct work and penetrations may be in the mechanical contractor's scope of work or the insulation contractor's scope of work, but the lack of it doesn't suggest poor construction and sealing of the duct work itself.

Your response to sktn about what's required here in California wasn't correct and that's what I was responding to. My understanding is that duct leakage testing, and only duct leakage testing (not blower door testing) is required when any equipment install or replacement work is done to a system where a portion of the equipment is outside the conditioned envelope. Which here, for what I'm sure is all but newish fancy custom homes, and even for many of those, is almost always. 90+ percent.

Yes, Elmer, I gathered that. I'm aware that CA has a duct leakage testing requirement when replacing HVAC systems. The point of my response was to differentiate duct leakage from building envelope leakage. Gaps around the perimeter of a duct won't contribute to measured duct leakage if the test procedure properly isolates the ducts. The gaps will contribute to building envelope leakage, but that's not part of a duct leakage test nor should it be.

I would think the connection between the duct and the register (not shown in OP's images) would be most important. If that connection is perfect, the space around the duct termination would be irrelevant. As it sets, an imperfect connection between the duct and the register would lose some conditioned air to the wall or floor cavity; not a total loss in that the interior of the house would be indirectly heated.

not a total loss in that the interior of the house would be indirectly heated.

The argument used by every sloppy HVAC installer who can't be bothered to seal joints, holes and gaps in their installation. I've seen my fair share of them!

Apologies to our indigenous demographic. But HVAC is long past long house technology. Perfect HVAC.

" an imperfect connection between the duct and the register would lose some conditioned air to the wall or floor cavity; not a total loss in that the interior of the house would be indirectly heated. "

In my one story house, the unconvered ground in the unsealed crawl space is visible through the gap. Would you still say that the loss is not a total loss? I think it would be and worse, the gap is an unsealed passage for outside, unconditioned air to come into the house. Just like a window left open

"Would you still say that the loss is not a total loss?"

If there was a .001% heat retention, it would not be a total loss. There are innumerable details that are not shared by the OP in the OP's situation, and impossible to accurately evaluate; so in essence we are talking theory to assist the OP evaluate the OP's concern with the OP's project. Your house is not the OP's.

I agree the information provided is incomplete but your comment was absolute and without caveats. If the situation is similar to mine, that the perimeter of the boot leads to unconditioned space (whether above or below, I believe your comment too is incorrect.

Do you know Loudermilk?

I don't know what you're referring to.

The majority of issues with gaps around HVAC supply boots installed in the first floor of a home over a conventional (vented) crawl space are associated with air from the crawl space being drawn into the home via stack effect and any negative pressure inside the home. I don't want air from the crawl space entering the conditioned living spaces of my home. Sealing around those gaps addresses the problem. The issue with gaps around HVAC supply boots installed in a ceiling with conventional (vented) attic space above is similar. In my (mixed-humid) climate zone that results in warm, moist air being drawn into the home, moisture condensing on the surface of the drywall around the HVAC supply and creating favorable conditions for mold and mildew growth. Neither is attributed to duct leakage.

I agree with Worthy about air leakage in conditioned spaces being dismissed as of little consequence because the leakage is into a conditioned space. The problem is that any amount of leakage reduces the amount of conditioned air being directed into spaces by design.

Exactly

The OP's space the OP's conditioned air would leak into is unknown. The likelihood of the OP's conditioned air leaking into the unsealed crawlspace of an ugly creature depicted as a dwarf is absurd. The OP has made no mention of where the air would go or if it would travel to such creature's space. Fabrication of other spaces effected other than those mentioned by reasonable commenters is ludicrous.

Energy star has a standard for duct leakage even if to conditioned space. That tells you something. But the degree to which it matters is certainly variable and it would not be as bad as leaking to an unconditioned space

In my area, they test duct leakage with boots over the registers - so it would catch this I would think. Also, in my area, townhomes are on slabs - nearly always - I can't find an example where they weren't despite crawls dominating in SFHs.

The orginal question was - is this normal? I would say that townhome construction is typically horrible and whatever can sneak by an inspector would be normal. Whether inspectors care about something like this is regional. I had a 2018 construction townhome rental and the air leakage from the garage was so bad - daylight under a door. Thankfully, we were EV only but that was unsafe by any measure.... And there must have been other leakage since the p[lace was obvious negative pressure when the HVAC ran.

"They test duct leakage with boots over the registers"

Hopefully that boot covers only the register and not the floor or wall or ceiling around the register. The connection between the duct and the register is part of the duct system that is being tested. If the boot covers an area more than just the register, it is also testing the air tightness of the house, not just the duct.

The issue of space around the duct at a grill is not an issue of HVAC, but of carpentry or drywall or other trades. It remains an issue for the home owner.