What are you expecting to fit in the chase?

HVAC ducts may take up the entire thing, leaving no room for plumbing lines, especially larger DWV lines.

Cam, I think this works fine. If it needs to be larger, just spare 1/2 of your hall closet there (or even chop off the back bathroom corner of that closet). Just be extra doubly sure your toilet area is large enough.

That powder room layout looks similar to how our plan is. However, since we are building a ranch, we added the "cubby" for small appliance storage in the pantry. Same overall powder room shape though, which works fine, IMHO.

what does hvac company say about this layout?

Kirkhall, I'll have to go measure some hall closets and see if an opening off less than 3' seems acceptable. You're right that this would be clearly comfortable if the closet only intruded a few inches, rather than a good 18".

Energy_rater, HVAC hasn't had anything to say, I'm going off of what my builder told me. If we have to go with a larger chase, there are contingency plans, which involve putting this either in part of the desk or part of the counter in the pantry (both of which also will take up part of a laundry room above, so they are doubly undesirable).

My hall closet is 24 inches... It seems sized right, especially if it isn't your only closet. In your case, you have a good-sized mudroom.

How does the sink drain without DWV in the chase?

This is heading towards disaster status.

I don't have a chase in my house. And, I have sinks and toilets that drain... So, it entirely depends on how that is all planned to be built. 6" plumbing walls can take care of the DWV, right?

equipment is in attic or basement?
isn't in info posted.

if this is a return chase make sure it
is sheetrocked & made airtight.
return leakage is a concern.

getting hvac company's input may help
to clarify install..for them, builder
& you. and they may point out any issues
you & builder may have missed.

I'd get their input also.

and yes..if you go to high efficiency gas
furnace..these are selfcondensing & do not
need venting like 80% furnaces.
in may of 2013 80% furnaces will only
be sold south of the mason dixon line.

for hvac industry to make this kind of mandate
backs up the savings of the more efficient
furnaces. once you upgrade to two stage heat..
you'll never be happy with single stage again.

lots of changes comming from hvac industry in
the next few years. for them to realize what efficiency
experts have been saying for years..is a good thing.

best of luck & Happy Thanksgiving.

brickeye,
Good point--I didn't think about that we need space for a vent. I imagine this can be done by making the wall to the chase 6", as kirkhall mentioned, or by making the chase larger. The rest of the plans have 2x6 walls for vents, I just didn't think about it here. Ultimately, this plan will be reviewed by my builder, who should catch these things--I'm trying to figure out the best placement now, and as I've mentioned, I have a few inches of wiggle room to accommodate things like a 2x6 wall instead of 2x4. So hopefully we're a ways from disaster status...

energy_rater, the equipment will be in the basement. Good to hear that high-efficiency is becoming the norm. This is the last major change before I get these plans to the builder, and we can go over these things in detail. I don't know who he is going to use for HVAC, but during the first meeting going over these plans, he got them on the phone to double check that we can do a single unit with dual thermostats for this plan. So we can verify these kinds of details, too. Thanks for your thoughts.

The chase size your contractor gave you is probably the inside dimension. I suspect the chase carries ducts to the attic for distribution so there are many other issues involved.

An alternate layout:

I think the toilet alcove will be too tight and needs to be switched with the sink in order to have enough room to access it properly.

I don't know why anyone would need a toilet space larger than 3 ft x 5 ft in a powder room. Often these dimensions are 6" smaller.

There are other layouts that would make the toilet less viewable from the hall but you would need to find out from the HVAC designer what the main duct size will be instead of relying a guess from the GC. Don't forget to leave space for insulation.

Here is a link that might be useful: min sizes

Renovator8, I appreciate the sketch. That definitely makes sense to put the sink as you have it, so I can make that wall 2x6 and put the vent there. As I've said, we can change the dimensions by a few inches by moving other things around as necessary. I was mainly looking to make sure this design generally worked--it's obviously not ideal, but it preserves some other aspects of the house that are more important to us than a particularly spacious half-bath.