I'm in GA with much the same weather. I question how much good encapsulation does without actually heating and cooling the encapsulated space. There's no way you could recoup the cost of installing one, even if you did the labor yourself. You'd be much better off replacing the ductwork for the HVAC, any way you can ride it out and time it to coincide with replacing the HVAC unit?

I'm not sure on the encapsulation as I've never done it, but I would do a very thorough inspection of the floor and walls in the closets and then the floor in the crawl space to see if you have mold/mildew in the structure. You might also look at a crawl space ventilator. Tjernlund makes one. Not sure if others do too.

Great comments everyone...price ...can be between $2- $3/sf. Anything more is overkill. As to the smell of some companies poly ... there was a run 4+ years ago where a handful of manufacturers that made a poly that was white on one side and black on the other and was reinforced. 1 of 10 after several months to a year started smelling like cat pee and got stronger. I ripped out a handful of these crawl poly's. I wouldn't blame the sealed company's only because we all look for a deal on plastic to pass on to you ... and the odor doesn't start for awhile...that could be 400 crawls in 6 months for a handful of us. That's 40 of them stinking and 30 notice enough. About the DIY'ers ... I have DIY hardwood floors ... brakes... toilets...etc ... It takes me 6 months to get a diligent guy up and going on crawls where I can let him run and inspect his work after. I couldn't imagine the $ lessons learned that a DIY'er gets into. Just know it takes one really experienced crawl space tech and 3 new techs to finish correctly a 2600 sf sealed crawl using 50 labor hours. Know that 50% of your homes air comes from the crawl space so a poorly prepped sealed crawl can trap some pretty nasty mold. Dehu's: to use or not to use??? Tests show that mold has not grown in sealed crawls that use a 4 inch air supply line per 1500sf with average height of 2.5 ft. Though the humidity reduces down in the South (Raleigh Area) to 68%-77% when sealed still leaves high humidity compared to the average homes humidity of 52%. But mold does not grow. Why? I can only guess ... A. Ground, where mold comes from, is sealed off B. Air is slightly circulating from the air supply line on your supply side. And a dehu wholesales $1000 average ... then install and electrical hardwire hookup and gravity fed condensation line. $1600-$1800 should be fair?? And that will take your humidity down to your chosen level ... most, I have found, chose 50%. Now here's the rub ... your dehu is taking up a chunk if not all of your energy efficiency that your conditioned sealed crawl gives to your AC system. So if you don't take the old insulation out and seal in the mold and the defication from the crickets, mice and snakes and you aren't getting any efficiency out of the sealed crawl ... then why invest $ at all??? No savings or better air quality. My recco: pull floor insulation, sanitize entire crawl for SUPERIOR lifetime air quality ... seal crawl and forget the dehu and gain 15.8% energy efficiency on new homes past 2008 ... higher efficiency for older homes. My pet peeve.... if a home has mold on the beams and evidence of cricket poop ... little black pellets all over the joists ... I wont seal it without pulling the insulation and disinfecting the crawl. But 95% of all companies seal the crawl trapping in ALL THAT MESS and that's there standard seal crawl practice. That should be criminal!!! Like all the contractors who knew back in early 1900's that lead based paint was killing children but kept using it because it was cheap ... until 1970's when a law was passed after ??? more than a million baby's past away. I feel mold in the crawl is that same issue that is slow to REAR ITS UGLY HEAD ... buyer beware ... short cuts can hurt you long term. www.SealedSolution.com

@T Burns I don't have an ATMOX system, but from what I've seen they have one inside and one outside sensor input on their controls. One outdoor should be sufficient, but for a large crawlspace I'd prefer more than one just because humidity CAN be localized if there is bulk water such as a flood or plumbing leak. My home had mold and rot only in certain areas--generally the east (downwind) side. The ATMOX optional louvers don't appear air-tight but passively flap down over the opening when the fan isn't running, like on a dryer vent. It's probably no worse than a typical sliding crawlspace vent. Plotting temp and RH over time is a great idea. From there you can obtain dew point and get an idea how often an ATMOX system would be able to run with just fans to keep the RH below 60%. With tight clearance between floor framing and the ground, the joists will track ground temperature by radiant heat exchange unless you have lots of airflow. You can get an idea of what RH will be at the joist surfaces by looking at those temperatures and figure out what max average dew point should be allowed. From there you can look at historical dew points for your area and get an idea of what percentage of the time fans can actually dry the crawlspace. As the ATMOX folks point out in their literature, it takes an extended problem to elevate wood moisture content enough to cause mold. You may be able to get by with a dehumidifier for half the year or less. But I would definitely not install one of these systems without a dehumidifier as backup, integrated into the control logic. If nothing else, it will come in handy if you get a flood or a fan goes bad and you need brute force drying. There might be some aspects of encapsulation that could benefit your situation, but I'm leery about arbitrarily introducing spray foam, foam board, or plastic-wrapped batts, like the Youtube encapsulation guys do, without really thinking through the moisture transport situation. You could easily end up trapping moisture or hiding rot or termite activity in an old house that wasn't built to modern codes. For example, my home has poly flashing between the rim & band joists and the brick, lacks a brick ledge, and was not built with pressure treated sills. If the brick really gets soaked, the framing gets damp. This is a once-a-year event at most, but it has a way to dry. The last thing I'd want to do is to trap moisture in the lumber. Also, my home's crawlspace vents also admit air to the gap between the brick and sheathing, and blocking those gaps with foam board will reduce ventilation behind the brick. Retrofitting an older home has to be taken case-by-case. I wouldn't trust most one-size-fits-all encapsulation contractors to consider that. I would probably never be totally satisfied with an ATMOX system, since the control logic isn't arbitrarily customizable, but it's an incremental improvement over full-time passive ventilation that we know doesn't work in summer. Automating the ventilation and combining occasional dehumidifier use may be all you need to banish the mold if there are no drainage issues. Thanks for the tip about the upcoming revision. I'll have to get in touch with them to see if they're adding fan diagnostics.