Why should you expect a stale basement smell if you have a properly constructed foundation?

I think leaving the fan on at all times is a bad idea, and a waste.

Two things for you to consider about the basement. Are you in a radium area? If so, the basement may have low levels even though tests say it is acceptable. Is there a thermal barrier between the basement and the next floor? If so, heat transfer between floors may be quite high compared to heat transfer through the house envelope making the air circulation that you describe superfluous.

Thanks for the comments....the problem is that our current house does indeed have a musty basement, and I am trying to avoid that with this new construction. In the new build, the walkout basement has ICF and insulation under the slab, so it is my hope that it will not have higher humidity and a musty smell. I was hoping that the suggestion to circulate the air throughout the house would help to assure a more even climate in the house.

Is there a scenario that you can see where I can accomplish a non-basement-like "lower level"?

Mechanical room and all HVAC equipment should be in the center of
the lowest level for best/even
distribution – not at the far ends of the house! Employ proper heat gain/loss
calcs, zoning, HRV/ERV and constant circulation
of air with variable speed fan coil unit or gas furnace.

IMPO

SR

Thank you for the answer. That answers my question regarding the continual fan operation to allow the air to circulate. Should I be concerned with the idea of having each unit having a zone on different floors?

In other words:

Unit #1 serves the right side of our rather long house, with a zone for main level and a zone for lower level.

Unit #2 serves left left side of house, same zoning.

( Lower level has 10'6" ceilings, main level rooms vary from 10' on up, with open kitchen and great room going up to 16', and open staircase to lower level.)

The heating and cooling loads for the two levels are going to be very different. It would seem to make sense to me to have a system per floor. The one for the lower level would be smaller than that of the top level. Both systems should be in the center of the house so the max length of the duct work would be about half the house length.

I hope you can find someone who can design a proper HVAC system. So far I have not been impressed with the proposals you have gotten so far. Your house is unusual, but it shouldn't be this difficult to come up with a plan that makes sense.

If you have concerns about the basement having a musty smell, then you should consider installing a dehumidifer.

Thanks again for the advice. We will keep looking at options.

Unfortunately I don't think that placing the HVAC in the center of the house is an option due to the layout of rooms. And I would prefer to not go the attic space, because it would cost much more to insulate the roof deck than the planned attic floor.

The take-home lesson for those planning your build: make sure you plan your HVAC during the design stage.

Two systems each with two zones (4 zones total) might seem inordinately complex if the same thing can be done with two systems without zoning. I think that is what Mike is trying to get at. That expressed, you need to zone because the demand in different areas is different. Maybe you really need 4 zones because demand is very different in each of the 4 areas. If that is the case, it can be split up a number of ways and saying what is best would require eyes on the plans and your plans for use of the house. If the lower level won't be used much, dividing it up so the whole right half of the house and the whole left half are served by separate systems would make less sense than an upper/lower system divide with old-school systems. With premium variable speed compressors and blowers, maybe it is better that way because they run more efficiently at partial capacity.

Guys, is having the air handler in the middle really such a big deal? Longer ducts mean more resistance, sure, but making the longer ducts higher cross section and the shorter ones lower cross section should work.

Yes, Ionized, you are right.....it seems likely that there is a need for 4 zones due to the overall length of the house (-110').

Will use the main level mostly, with master suite area taking up 1/3 of the level, great room/ kitchen taking up the remaining 2/3 space.

Lower level has 2 bedrooms, bath and storage under the master suite level, with a family room, bar, theater and another bedroom under the great room/kitchen. Open staircase centralized, going from great room to family room. Bedrooms here are for when the grown kids come to visit....a couple times a year. However, I am sure that we will use the bar and theater more often.

While the load for the lower level is smaller than the main level, it still seems like we would want separate zones on each level to address the needs of the far reaching rooms.

If anyone wants to throw out any other thoughts, I would greatly appreciate them!

Ionized mentioned radon and nothing was said. Do you know the radon level in the basement? Do you have mitigation? It is better to test and mitigate than to ignore it and be exposed to radiation in your home for years on end. You wouldnt ignore it if you could smell or see the radon would you? Houses with basements are at increased risk, and it does make its way up to the main floor from a basement.

http://www.epa.gov/radon/pubs/citguide.html

We have a lot of shotgun houses in New Orleans :-)

You are right, I forgot to mention that we will have a radon control system installed at either end of the house.

The two systems can each of two zones. That should not be difficult.

The systems should be installed as close to the center of the house as possible. Installing them at the ends of the house would be a mistake in my opinion.

Mike, I wonder what your opinion would be for a "2nd best scenario". The center of the house is not available to place the HVAC system. I would not have to place them on the extreme outer wall. I could maybe locate unit #1 about 35' from the outermost left-hand wall, and unit #2 about 17' from the outermost right-hand wall. (110' length of house)

Assuming this placement, what do you think about having each unit serve both floors. Or should I try to have one unit for main level and one unit for lower level, with rather long ductwork?

This is a difficult question to answer without a thorough analysis of the building plans. You want to minimize the length of the duct work. I suppose each unit could be zoned for the upper and lower levels. You also have the added complexity of varying ceilings on the upper floor. Moving the systems towards the center improves the distribution.

Thank you for the feedback. It helps.

We will definitely keep evaluating our options.

For a house that large you also need to consider how to break it out into frequent vs. infrequent use areas, and design the zones accordingly. For example, if you have times where some parts of the house are not occupied you can put them on a different A/C unit or zone and leave the temps set to a more moderate level.

We built a relatively small single story (2600 sq ft) and they put the main part of the house (great room, kitchen, dining, living) and the master BR on the large A/C unit. The other 3 bedrooms were on the other (smaller) unit. When our kids were old enough to move out we were able to have the MBR and the main house area at one temp and set the 3 unused bedrooms at another temp.

Bruce

I vote for a 3200sf house with 1 hvac unit.