Location please...

Why not run a load calculation for correct sizing?

What is fuel source for heating and cooling?

Post back!

IMO

ditto TIgerdune's post.

smallest central split system is 1.5 tons.
cost is the same, or very close to, as 2 ton system.

in my small home with not nearly the insulation
in the walls..I put a 2 ton heat pump
15 SEER with variable speed air handler unit.

my utility costs are very low and comfort is
amazing...and I still haven't insulated the floors
of my house on piers.

with supply 11 ft overhead you are probably
the only one who will notice the difference
in size of supply plenum. if it is exposed then
you can always paint it to match the ceiling
so it isn't as noticable.

understand that if your house is very tight, as in
minimal air infiltration, you may need to look
at adding fresh air. review ASHRAE 62.2 ventilation
strategy.

best of luck.

Location is Okla. City, gas furnace. I know you are correct about the load cal. but the one time I looked at a Man J it seemed way over my head. Seems most techs just want to use a rule of thumb. Do you know of a simpler load cal?

What is the purpose of the variable speed motor besides maybe energy savings? Does the variable speed adjust it's self to the duct size of what. Would the coil not freeze up if you don't move enough air across it?
When I get back in from work tomorrow evening I will post model numbers on all equipment. I think it is 16 seer system. Any thoughts on mini ductless split systems?

Is there an attic up above the ceiling? How much is the insulation below the roof line?

You can do your own load calculation with HVAC Calc for $49. The link is below. It is not too difficult. The load calculation on a small structure can be deceiving. What are the average summers highs and winter lows for your area?

The ductless mini split is an option. It may be cheaper to heat with a gas furnace, but the difference is probably small. What size and efficiency furnace did the contractor deliver? Do you have the model numbers of all the equipment?

Here is a link that might be useful: HVAC Calc

The link thing is pretty simple and worked well for me.....

Based on our personal experience, being half a continent due east of the center of the northernmost hanger at "Guthrie-Edmond Regional Airport", you are making much to do about nothing. If you are on the gas pipeline, get a nice small gas fireplace (or two, the smallest model you can find in a bedroom is very nice to have), and relax. And with your level of and attention to insulation and infiltration, you will have no issues at all with keeping cool with a single 15000 BTU window A/C.

If you go with a 2 ton HP/gas HVAC unit, your unit will cycle endlessly, and you will be opening and closing windows and doors on all but the coldest days. And in the summertime, you'll never get "it" quite right for the month prior to the dog days getting here and the month after they're gone, and will find yourself a bit too cool many a night, and a bit too warm on many others.....

And, like energy _rater says, with a house that small and well sealed, you will need some sort of heat/air exchanger and a dedicated combustion air intake for whatever combustion based heating source you choose to install.

LOL..... We are right now building our new permanent just for two house, that has somehow ballooned to 736 sq ft. As we're 1.25 miles from the center of the road, it's wood, propane, electricity, wood --- and/or solar. We are opting for2X6 and R-19 fiberglass beneath 1" polyiso insulation. As we are fortunate to have several thousand times more wood than we could ever possibly need burn we are planning on solar and wood being the primary sources of heat and hot water. And an "exposed " ceiling with 1" of polyiso on top of 8" fiberglass. As we are so very fortunate as to have several thousand times more wood than we could ever possibly need we are planning on solar and wood being the primary sources of heat and hot water. We are putting in a small wood cook stove in the kitchen right smack in the middle of the house, and a very simple ventilation system in the crawlspace abed room closet that basically does nothing except move air from floor to ceiling in the summer time, and ceiling to floor all fall and winter.

800 sq ft, we applaud you and your efforts! 800 sq ft! Little for the tax man and less for the gas/electric/water folks too. Why with LED lighting and every water saver thing that you don't mind using with a big garden and a freezer full of meat and other goodies, you just might find yourself living for just about free!

Here is a link that might be useful: Manual J Online Load Calculator