Since this is new construction, I will assume that building and insulation qualities will be way above average.

In the South, it is quite common to locate a furnace and ductwork in a crawlspace. You should have good ventilation and the ductwork should have R8 insulation or better. Furnace will be leveled and placed on cinder blocks off the ground. Of course crawlspace should have poly covering. Builder and HVAC worth his salt should know all of this.

If ductwork to be placed in attic, I do recommend it be conditioned. Regardless attic should have good insulation and ventilation probably a ridge vent along roof line.

For your location, cooling is more important than heating. The South has relatively moderate winters.

If 80% eff furnace, I would add a high eff heat pump.
If 95% eff furnace, then I would add high eff AC.
As far as SEER rating, at least 16 SEER. 25 SEER is absurd with no payback unless you just like wasting your money.

If not individual room returns, then I would want minimum of three central returns strategically placed through the home. You would want a pleated filter media cabinet installed on return end of furnace.

I prefer Carrier or Trane over Lennox.

IMO

tigerdunes, thank you for your response.

Yes, house will be well-insulated. 2x6 exterior walls which is R-19 with 1" polyiso foam boards installed over rigid sheathing. Probably R-50 in attic unless we do closed cell spray foam in rafters in which case I don't understand the R value. Marvin ultimate clad casement windows. We will build to Earthcraft standards which program is run by Southface Energy.

We will use the poly ground cover and pour a thin layer of concrete on top. The crawl space will be unvented so not sure how to vent furnace? I assume the furnace would need to be a "horizontal" unit for the crawl space. Do Carrier and Trane make such a unit?

You said at least 16 SEER. What is the highest SEER we should consider? I just assumed we would install the highest SEER available. Of course we are planning now and have no price information so that could change things.

Furnaces are horizontal.

High eff condensing models 90+% eff will have to be vented through an external wall with a dual pipe kit, one for waste gas, one for fresh air combustion. I have a concentric pipe setup. About two ft off the outside external wall ground not directly under a window.

Mine is a two stage var speed Trane, never any issues.

When you get over 16 SEER, I think one has to weigh the cost difference versus possible savings. It has been my experience that manufacturers/ dealers make the upgrade very difficult to justify.

IMO

I will compute the payback period for each system we consider but I am not limiting my choice based solely on that. Of course, I am not even close to getting bids so I may change my mind when the numbers roll in.

The Trane xl20i has two compressors. Is that an advantage over a single, two-stage compressor?

Many folks seem to not like Lennox. What is wrong with Lennox?

The XL20i does have two compressors and the split between low stage and high stage is 50/100% output.

The single step two stage compressor has about a 66-100% output between low stage and high stage.

Of course the two stage step condenser is less expensive. You will get other opinions but I don't think it's a big deal in comfort. Certainly there is no empirical evidence on reliability.

I don't think Lennox deserves to be discussed in same sentence with Carrier and Trane.

IMO

why not design the house with both equipment
& ducts inside of living space?
now is the time to do this...and it is a win/win.

putting ducts & equipment in hot attic is a crazy
thing to do...even though we do it too often.

but..with high efficiency equipment, the plenum,
ducts & supply boxes condensate because air
is colder leaving the unit.

same holds true in crawlspaces..condensation.
even putting hard duct in a crawlspace, critters
tear off insulation for nesting & enjoy the
cooler/warmer space. with exposed metal
they also have a water source.

architects & designers fail us when they don't
design with ducts & equipment inside the
conditioned space where we live.
using foam insulation has become very popular
to create a semi conditioned space...but it comes
with a high cost to the homeowner, esp with
closed cell. (we use open cell here in La.)

I find the best range for efficiency & dehumidification
to be the 15-17 SEER range.
also, if you are foam sealing the attic with a 80%
gas furnace there are considerations for combustion air.

best of luck

ERL, thanks for your post.

The crawl space will be conditioned just not sure about the attic at this point. The crawl space will be completely sealed and access will be somewhere inside the house.

When you say put equipment and ducts inside the conditioned space, are you referring to a utility room that would hold the furnace? How would the ducts be distributed from there?

The crawl space will be conditioned just not sure about the attic at this point. The crawl space will be completely sealed and access will be somewhere inside the house.

how high off the ground will the house be?
putting ductwork in crawlspace is usually a bad idea
when crawlspace is low to the ground.
with the best of intentions, hvac companies often
have plenums too close to the ground.
ducts also submit to gravity and unless properly strapped
will, over time, sag.

hard pipe ducts?

mastic seal of all joints in 90's, at least 3 screws
holding each connection, long seam in hard pipe mastic
sealed. supply boxes mastic sealed to floors, and
each plenum connection to equipment mastic sealed.

then metal strapping is screwed to hard pipe and
to floor joist to level & support ducts. hole in
hard pipe from strapping screw is sealed.
then wrapped with R-8

it is difficult to get hvac co to do this type of install.
even paying extra, you should keep an eye on the
install by going into the crawl & making sure
prior to install of duct wrap.

ductwrap seams should be overlapped, stapled
& sealed with fsk tape.

When you say put equipment and ducts inside the conditioned space, are you referring to a utility room that would hold the furnace? How would the ducts be distributed from there?

this is why the need to see the floor plan is necessary.
putting equipment into a centrally located closet,
with return at bottom of closet, platform sealed to walls
with equipment & supply plenum intop of closet.
ducts are distrubuted from supply to rooms via
furrdowns with ducts inside furdowns.

best of luck

I'm having difficulty picturing the furdowns. Do you mean the furdowns would be just below the ceiling and hence would be visible within the interior of the house?

BTW, are you familiar with Southface Energy Institute?
We are going to build thru their Earthcraft program and I assume we will get some final HERS rating.

On the A/C, I really like the Trane XL20i. It has two compressors which seems to make a lot of sense. I may shy away when I get the costs in...

BTW, are you familiar with Southface Energy Institute?
yes, my study guide for my national certification was through southface. when I had questions they were very acessable.
to this day, I use some of their pdf files to advise homeonwers on air selaing.

not familiar with earthcraft project though.

as for furdowns being visible..in some cases yes.
other homes have a central hallway that can be
furred down for ducts. other homes incoprerate things
like trey ceilings to hide ducts.
in my house the only visible fur down is in
the kitchen. thru this furdown I serve living room.
office & one bedroom along with kitchen. the
rest of the fur down is in the top of a closet for
other ducts.

design stages is the easiest time to design for
the ducts inside conditioned space. there are
several ways to do this depending upon layout
of rooms in the house.

a lot of time you see side wall supply grills
the ducts are furred down. other times they
are attic fed into side of wall (or basement I
suppose..having no experience with basements).

flw's falling water house is a good example of how
incorperating ducts in fur downs can be appealing...
IMO.

best of luck.

It would be easy to hide ducts in the perimeters of tray ceilings as well as hall ceilings.

What if we decide to condition the attic? Spray foam on rafters and seal the attic. Would ducts be okay in a conditioned attic? It would put the supply ducts in the ceiling of each room which I assume is good in a cooling climate?

I will defer to energy rater.

But if this is single story home with 8-10 ft ceilings, I prefer ductwork to be in crawlspace and registers to be on walls close to floor. And I do recommend individual room returns over central returns. If any of the rooms have a cathedral ceiling, special design should be thoughtfully given for proper heating and cooling.

IMO

spray foam in rafters for an unvented attic..it is an option.
it allows the hvac contractor to do a regular install instead of configuration of fur downs/trey ceilings etc.
but...unvented foam sealed attics are Semi-conditioned,
not conditioned. the ambient temp & temp inside of the foam sealed attic are usually within 10 degrees of each other.
and, the tradeoff for spending 3x the cost for foam is smaller tonnage hvac system. so hvac co needs to be on board.

using foam covers a multitude of building problems..oversized holes for plumbing & electric. IC instead of ICAT recessed lights, oversized cuts at bath fans, stove vents, fireplaces not sealed off in attic and thermal bypasses all become non-issues when the air & thermal barrier is moved from attic floor to roofline.

as we put more efficient hvac equipment into attics,
we have to be careful. these units produce colder air
(our issue in summer) and plenums condnesate in an vented attic. this is one of the reasons that foam has become such a strong product, because now the attic isn't
as hot, and colder air in the plenum doesn't cause as much condensation in foam sealed unvented attics.

I'm trying to get my page online for videos up and running.
I just uploaded video of an open cell foam install. the videos show how to seal the roof to attic floor (soffit/eaves) connection properly, how to seal at passive turbines on roof (for existing homes) and the last is after rafter bay has been foamed, how to come back & fill in voids & low spots.
later this week I hope to have time to get it up and ready for viewing. drop me an email & I'll share the link. I'm getting pros & cons as to making it open to public...which I'm inclined to do...but have gotten feedback against it...so for now..you'll need a password.

as a homeowner you have to be very selective in chosing
a foam company. it isn't the owner/salesman that makes a good install, but the person doing the install.
if they rush...they miss areas, if they move too slow the job takes longer.
temps of mix,combo of chemicals, roof temp & moisture content all have to be consitered.

I'd expect to see pictures of previous installs, be allowed to go on a job to see the process & to be able to call previous homeowners to see if they achieved savings & comfort after the install. ..yeah...I'm picky!
but I've seen some really bad installs over the years. finding a good company, with an experienced installer...takes time.
as I test the air tightness & measure the depth of the
install, companies locally know that they have to meet
my standards.

here in La., we use open cell foam...what is the type for your area...open or closed?

if you go this route...interview companies. make sure you know going into it that you still have to meet the code requirements for R-values. with closed cell at R-6-7 per inch & open cell at R-4 per inch..the right amount of inches have to be installed. the whole 2-3" 'performs as' is hogwash. 'average' fills are hogwash. you want an install
with no dips (low spots), no voids or gaps & a good seal at the attic floor/rafter area so that no hot humid air enters at
soffit area of the house.

I'm attaching a picture of a good install of open cell.
note that the rafters are 2x6 and are well filled between rafters , faces of 2x's are covered. the bid was for 7", but
at lowest point the foam is 7" thickest point closer to 8".
note the soffit (roof to attic floor) also. this is what is necessary for air seal of attic.

fwiw..the company that did this install, the owner is the installer. in my part of La., these seem to be the people you get the best install from. not so much with salesman
selling job & installer doing the job.

best of luck.

As this is new construction, have you considered geothermal? Your first costs for installation are the lowest.

Just a thought.

SR

erl, thanks for a great response.

In Atlanta, insulation companies advertise both open and closed cell foam. Most seem to push the closed cell since it has a higher R value per inch. I guess it pays more also so we'll see at that time.

We built our current home to Earthcraft standards using cellulose and the guy who owned the insulation company was on-site throughout the entire process. When the Southface guys did the blower door test, it did not take long and they looked at each other and said "wow". That was a good sign. It's a great suggestion and I will seek out the same company or one like it whether I do foam or not.

I'll email you to get access to the video.

fsq4cw,

Thanks for your suggestion.

When I get costs and options, I will have a lot of decisions to make. I will do a payback calculation but I am not holding to payback only. I want a house that is extremely energy efficient. Of course, where the rubber hits the road is money. So I won't know until the time comes but geothermal is one of the options we will crunch the numbers on.

tigerdunes, ceilings will be 9 feet. We may raise the great room to 11 or 12 feet but not cathedral. Fell for that trick in our current house; won't do that again. We have always had individual room returns so will keep that scheme.

Thanks again.

This post was edited by john_wc on Tue, Jul 30, 13 at 17:43

for fsq4cw

OP has nat gas availability.

I think geothermal would be a poor choice especially considering nat gas and Southern location.

IMO