The insulation of the spaces should already have been determined by the building designer and the HVAC system should already have been designed with that information as a given. This is not the time to be adding insulation.

Similarly, the number and size of supply air registers and return air grilles should already have been determined by the HVAC system designer. Your task, I suspect, is to help decide where they should be placed in order to avoid conflicts with furniture, etc. although there usually aren't a lot choices if you want the system to work properly.

It is sometimes important to have return air grilles in large private rooms so the return air doesn't have to pass under a closed door.

The only piece of advice I was given is that since we are planning on having a freezer in our pantry we should have a return grill in there.

It is important to have a return, jumper duct, or pass thru grill in any room that has a door with close fitting carpet beneath it. The supply air needs to have a way out of that room in order to prevent pressurization losses.

I placed a return in every bedroom. I also had my returns low with my registers high -- only used for AC -- radiant heat system.

If you live in a cold climate, and your bathroom & MBR are on the north side of the house and have more than 2 exterior walls, be sure you have sufficient ducts.

We put a lot of thought (and insulation) into our bonus room, to the extent that we even had an entire heating duct routed through conditioned space along an interior wall which made a long bench, but missed the boat on the master suite (2-3/4 exterior walls plus a garage wall).

Also, I knew exactly where I wanted most of my furniture, so was able to direct the HVAC guy to mark an adjacent set of joists to put the registers in in several places, instead of the ones he originally chose.

Anne

The HVAC designer will take into consideration the heat loss from each room when designing the size of the ducts. Don't try to size the ducts yourself.

macv, our HVAC designer is the one who determined one toe kick register would be sufficient for our bathroom that is about 10'6 x 10'6 and split into 2 parts. The register doesn't even keep the 5'6 x 10'6 part on the ICF north wall (with the tub on the ICF garage wall) warm enough. He never showed us a plan--just walked around with me and pointed to where he thought the registers should be.

DH was the one who had all of the discussions with the HVAC people as to everything having to do with the geothermal. I remember lots of discussions about heat loads(?), and sizing the furnace due to our extra tight construction, and about other parts of the house, but don't remember them talking about the master suite.

As with many subs, things can get missed. I'm mentioning this to give a heads up that people need to think about as many aspects of their new house as they have time for in order to avoid misses like this one. If I had just thought about the fact that all of those walls were exterior, I would have asked questions that probably would have resulted in more ducts in this part of the house.

Anne

if you seal the walls of the bonus room on the attic side it will be affordable to heat and cool, and comfort will not be an issue.
we use a foil faced foam sheating board to do this.
this creates an air barrier which allows the thermal barrier (insulation) to perform.
the temp gain from attic space on the other side of these rooms usually result in oversizing of hvac or adding more supply grills, when actually treating these as exterior walls is the key.
temps are much more extreme in attic space than outside temps, but are usually insulated
but not sealed.
you would never leave insulation exposed on ambient walls..
why do it in a space with more extreme temps?

best of luck.

jimandanne_mi
You are confusing an HVAC system designer with the system installer. Get a designer who will determine the heat loss from each room and size and locate the ducts, grilles, and registers appropriately.

Our geothermal guy had a number of people in-house, including their guy who went around with me and marked where the registers should go. They subbed out the installation to someone else.

The geothermal people did the heat loss calculations for the whole house; I would assume this means they went room by room. Their final number was very close to the one DH came up with. But he never saw the room by room calculations, and didn't see a need to look at them at the time. They're professionals, right? Their total agreed with ours, so why would we ask to see how they got it? But that's the point of my earlier post.

Anne

It's not the room heat loss/gain numbers that you need when locating the grilles and registers but the size of the air ducts supplying and returning air for the room that have previously been sized to meet the heat loss/gain needs. I wouldn't accept any HVAC design without duct diagrams in order to avoid conflicts with other trades and to prove it had all been carefully thought out nor would I walk around in the house making decisions without that information. Trying to tune a poorly designed duct system after it has been installed saves no money and is a pain no one deserves.