You'll have to dig the footings so deep that you will be more than halfway to a basement. Do the basement.

You could insulate the rafters and put the furnace and the ducts in the attic.

Do you intend to trey every room and hide the ductwork in treys? Or run ductwork and cover it up blown in insulation?

Whatever you do, I would avoid furnace, AC coil in the attic. If it leaks and it always does you will be replacing the ceiling.

Have you explored geothermal heated floors?

Live_wire_oak: water table is very high as we are ocean front. We plan to build three feet above grade and backfill 1'

Reno: The furnace will be in the mechanical room and many sites say even with good insulation duct work shouldn't be in attic. We get temperatures of -30F+ in the winter.

Brian: We were thinking 8' ceilings in hallways and trays where needed.

Mama Rachel: Our neighbor just did geothermal and it was very expensive as he had to drill a well, I believe, 200' down.

?water table is very high as we are ocean front. We plan to build three feet above grade and backfill 1'. ?We get temperatures of -30F+ in the winter.

So your slab will be 3' above the grade? vs 10"?

Pro: 2' after 1' of fill is added. The garage will be 20" lower and the front of the house that is exposed will have a deck for the full width. The sides are on wooded areas and the back, water side, will also have 1' of fill added with a full deck.

Plan "B" would be the same as above with a 3' mechanical only crawl space. (see other posting"

If the insulation is in the rafters the attic would be conditioned and the ducts would be insulated. The advice you read about not putting ducts in the attic assume the attic will be cold.

In the Boston area I've never done it any other way. Its a much cheaper alternative to a dropped ceiling.

Renovator8: Interesting, no one has given me any hope of an easy solution. Could you elaborate a little more on how this is done ie where is the moisture barrier and insulation installed in relation to the back of the ceiling gyproc?

For your climate I assume there will be a steeply sloped roof hopefully consisting of rafters rather than trusses.

It is possible to insulate between the rafters by either sealing the attic with foam (unvented attic) OR provide a ventilation space between batt insulation and the roof sheathing with vents at the eave and ridge.

If the attic is not habitable there would be no reason to finish it with gypsum board or provide a vapor barrier for either of the insulation options. If the space has mechanical equipment that will need servicing, an intumescent coating might have to be applied to foam insulation to meet a thermal barrier requirement. The weather/moisture barrier would be some kind of roofing over underlayment.

x2 on foam insulation in rafters for unvented attic.

or if layout of house allows, you may could
locate the return & furnace centrally & fur down to
each room. works well if you have a hallway
with rooms off the hall & family areas at end of
hall.

post your plans so we can see.

best of luck.

energy_rater_la

Floor plan attached. The mechanical room is in the upper left above the stairs to an unheated storage area.

Thank all for the advise. I may have confused a few people by not explaining that the heat pump will be in a conditioned mechanical room.

I got some feedback on how it is usually done in this area. It is recommended that you get an HVAC expert to sec out your system and the location of the ducts. You would then order your trusses with "duct chases" cut out of them. The contractor then builds open boxes out of plywood for the chases and the ducts are installed. The attic is then insulated, the HVAC system is tested for leaks etc and then the ceiling material is installed.

If there are tray ceilings or rooms with lower ceilings in those areas the duct chases would not be required.

What are your thoughts on this solution? It sounds similar to what several of you have suggested.

Sorry, my other discussion on "Three Foot Crawl Space" has ended up as a duplicate posting.

Yes, the duct chases are built into the bottom of the trusses and insulation is blown in on top of them and on the attic floor.

That is not what I was recommending. It involves special trusses called PLENUM TRUSSES.

Here is an explanation of the Plenum Truss concept from Green Advisor:

I don't buy the claim that the ducts don't need to reach the outside walls in a cold climate.

It seems like something a builder would use to increase profits. I wonder if you would benefit if you were not acting as the GC.

renovator8: Thanks very much. Your plenum Truss is the same as my "duct chase. I guess I was not explaining well, a box built into the bottom of the truss.

So you are saying that the ducts should reach the outside wall? That's what I would like although some suggest it is not necessary in a well insulated home. I will have 6" insulated walls, lowE argon triple pane windows and 3" of XPS under slab.

It might work but I would recommend a tall ceiling with ceiling grilles that throw air toward the outside wall. I confess I have a strong dislike of HVAC grilles in the middle of ceilings.

Perhaps the difference in our approach is due to the fact that none of my clients has ever been willing to give up the space in the attic and has therefore been quite willing to pay the relatively small price for making it useful. A lot of my work when I first started out was converting attics into bedrooms. Maybe their attitude its due to old-fashioned Yankee frugality. None of my clients has ever been willing to give up a basement either.

If you're on a slab, you could have radiant heat in the floor fairly affordably and efficiently. You say AC is not that important, so you could just add a mini split or two as needed. I had a house with a slab and radiant heat served by a standard water heater. It worked very well for me, and avoided duct work altogether.

Folks,Thanks for all your advise.

mermanmike: I am going to do more research on the infloor/mini split option. I had that as one of my original ideas but was thinking at that time that the mini split would be my primary source for heat. We get a lot of drifting snow and I was worried the outdoor unit would be plugged and stop working so I scraped that idea. The fact that we spend our winters south made that option even less interesting.

With your suggestion I would use ductless mini splits for air and also heating but shut them off when we are away in the winter.