Austin is the only city that I work in that requires manual J. And only on new construction. They really don't care what is says as long as the blast and cfm test they perform when house is completed matches manual j. You could put a 5 ton on a 200 sq. ft. room and they wouldn't give a rats butt as long as paperwork matched.
It ain't happening man. Austin is the only one locally that requires any of this. Austin has Austin Energy which is the electrical provider. It also provides electricity to other areas with Austin addresses but not really in Austin. Texas is weird. They don't require any of this either. Some don't even require permitting for changeouts, but they do for new construction, which is little more than a money grab. An inspector in one of these areas mechanical inspection was poking his head in the attic to make sure we actually installed a furnace and coil per the permit. Nothing else, he didn't crawl into the attic at all. I did a job about 2 months ago, it was an add on to a house in no man's land between Austin and Round Rock. It was MUD controlled. No inspection or permitting required unless you touch the water line. At any rate, the guy paid somebody to install furnace, coil, condenser, ductwork for said addition. The guy installed a used, aged, gutted gas furnace, layed on it's side, no flue, no gas run to it. They did some monkey business to get the blower to run, all controls and safeties ripped out. Needless to say it was irrepairable. I installed new system and brought to code as much as humanly possible with what I had access too. I did another job about a month ago, not too far from this first abortion. Homeowner adding on to his house, doing work himself. I just added ducts to addition, did to Austin code since most restrictive. Once again, no permits, inspection, etc.... For me its good, I do things correctly, not much into cutting corners, no hassle with over zealous inspectors. But its also bad, cause I get called in to fixed some FUS sometimes. I've seen some really bad jobs that would make wall of shame look like wall of pride.
I am building a new house in the piney woods of east TX. H/C area of the house is 2800. All windows face east and west but most are under covered porches. The sun doesnt really hit the windows due to so many trees around. Spray foaming walls and roof deck with open cell foam. Had the HVAC contractor come out, (very reputable, highly recommended,never heard any complaints, excellent service company, does many foam houses) come out. This is what they recommended from looking. They had not ran a Manual J yet and are going to. They said 1 - 4 ton Carrier Infinity variable speed Heat pump to service most of the house, and 1 - 2 ton to service the master suite, utility, mudroom. The spray foam guys came and said that is way over sized and they ran a manual J that said I need 3.4 tons total. When I told the HVAC guys, they said that is true, and that I will need approximatly 3 tons total to cool the house. They said the reason they went with a 4 ton and 2 ton variable speed was 90% of the time I will be running both units @ 50% essentially 3 tons. In the case we have a bunch of people over or it reaches the 110* days it usually does in June, July August in TX, that it then has the capacity to take care of that. HVAC guys said their # 1 concern is humidity control and comfort. Does setup they recommend seem appropriate?
These efficient homes need fresh air to purge the indoor pollutants and renew oxygen.
2,800 sqft of air tight home needs a fresh air change every 4-5 hours when occupied. This is about 80 cfm of fresh air. How? You have cloths drier, kitchen hood, and bath fans that need make-up air to exhaust air. How?
You are rightfully concerned about maintaining <50%RH during the low/no cooling loads with high outdoor dew points. Also consider that the occupants in a home add 1-2 lbs. of moisture per hour. There will be days that you have 2-4 lbs. of moisture in the home and no cooling load.
The simple solution would be a whole house ventilating dehumidifier. Units like the Ultra-Aire 105 H provide fresh air when the home is occupied and will maintain <50%RH during damp times of the year.
This is the most efficient Energy star rate dehu available.
Ultra-Aire is co-sponsor of this site.
Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
Use +Merv 10 air filter. -Don't forget the "Golden Rule"