Hire someone that can do blower door tests to set standards that the contractors need to meet for envelope leakage and for duct leakage if the ducts are going to be outdoors. If ducts are located outdoors, reconsider putting them inside the envelope. Make sure that pressure imbalances do not make your air handler into a power vent.

A one-room zone in a 3800 sq house? You might have to use a mini-split.

I would want zoning controls with variable speed HP condenser. Look to Carrier/Bryant and Trane/AmStd dealers.

IMO

Do you know how much you will pay for propane and electricity? It may make sense to install heat pumps and use the propane as a back up. The estimated costs can be calculated based on the current pricing.

How large is the mother-in-law suite? I would recommend two separate systems for the main house and the suite. The 450 bonus room could be zoned off the main house system, or you could install a mini split.

Since you are on a slab I highly recommend you not install the equipment in the attic. Build a utility room on the main level.

The spray foam is nice, but it is expensive. Find out the additional cost and R value you will get with the spay foam. It is probably not worth the additional cost, but it is worth investigating.

In additional to the load calculation, ask how the ducts will be run, sizes of main ducts, returns, what filter and thermostats are included, etc. You HVAC quote should have all model numbers with a detailed description of all work to be performed.

use foam insulation in the roofline & put foam
sheathing on exterior of walls.
this is the best bang for your buck.

then size the hvac system with load calcs
including the proposed tightness of the house
that the spray foam & foam sheathing will
provide.

bigger isn't better. oversize & you'll suffer
high RH for the life of the unit, along with
higher upfront equipment costs & higher
utility bills.

these are the things that save us money, provide comfort
& lower utility bills.

invest in mid range SEER/HSPF rather
than builder's model.

if hvac co still insists on oversizing & you can't
stand the load calc ground, then invest in two
stage equipment that will operate in low speed.
more than you'll ever need, but hvac co will sell tons
& higher priced equip. at abigger upfront cost to you.
otherwise single stage condensing unit & variable
speed air handler unit will work well at controlling
indoor RH.

if my Mom had lived with me, I'd have put
a mini split for her area of the house.
there were days when she would be cold with
the a/c on. kinda crazy for a/c to be on & using
an electric heater in one room for chilled parent.
mini split would give her control over her area.
just something to think about along with
wider doorways & handicap rails in bathrooms.

best of luck.

One thing that would be an interesting exercise is to do the load calculation with fiberglass batt insulation and then again with spray foam. It should be easy to change the R values of the exterior walls and attic once the data is set up. You could take it further and do spray foam on walls or attic only to see what impact it has.

The spray foam may or may not allow you go down one size in equipment. You should see a decrease in the heating and cooling loads. Calculate the percentage decrease, and that will give you an estimate of how much energy you will save by using spray foam insulation.

If you do these calculations, please post the results. I would be very interested.

the foam on the exterior of the wall adds higher R-value
to the wall.
however the foam on the roofline's R-value would stay the same...different
product, installed to same R-value.
where the foam would show up in the load calc
is in the tightness of the house.

choices are leaky average & tight. you want
the latter choice in your load calcs.

make sure that it is understood that the house
will be tight, and as a result of the higher cost
of the foams, the lower cost of a smaller hvac
system is the tradeoff.

lower equipment costs & lower operating costs
are also. bigger is not better if you want to control
humidity inside the house.

best of luck.

Hi all,

An update on our situation. We found out that we DO have natural gas to our neighborhood. We are currently getting bids for spray foam insulation and A/C units. I have included Manual Js calculated with spray foam. They also provided Manual Js for batt insulation, and I can post those if needed. We are getting different advice from different people and I'm a little overwhelmed right now! We need to watch the budget as much as possible, but we would like to have a tight house, low energy consumption, several zones (definitely one for my mom's area / or a mini-split?) and would like to incorporate smart home features.

We also really like Trane products, but are willing to go with other options if necessary. I'm including screen shots of the manual J calcs.

The company that calculated the Manual Js bid approx $10,000 for:TRANE - FOAM HOUSE -
4TWR5049E,
TEM6AOD48H41, 15 KW, Time delay relay, Control tcont624 - 15 SEER
HOOD VENT
R-6 DUCT
GAS HEAT
ALL
UTILITY AN BATH FANS 50 CFMS
FLOAT SWITCHES
JUMP
DUCTS IN ALL SECONDARY BEDROOMS & STUDY
RETURN
AIR IN MASTER

This appears to be a discontinued model??

We also received a verbal approximate estimate (written estimate is being prepared) of $17,000 - $20,000 from another A/C company for the new model of the unit above. What gives? That estimate is double the first estimate!

I am also awaiting bids for spray foam insulation.... a little scared to see those....

What do y'all recommend?