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

Zoe52 - The required elevation is based on the 100 year flood height for your area, plus 1 ft. Our situation is very similar. We had to build up 4 ft and wanted an enclosed crawlspace as it is better for our humid climate (we're in SC). Since we had to elevate for flood reasons, we still had to have flood vents. We were able to use "SmartVents" which are insulated for a closed crawlspace and balanced so they will open to the pressure of rising water. They are pricey though! The crawlspace walls are insulated with foam and the floor covered with heavy plastic - 8 ml I believe, it's been a while since we installed it. We are using passive venting with a 'through vent' in our pantry which has it's own returns. We did it ourselves as we are our builders :) You can hire a company to do it for you or your builder can do it fairly easily with some directions. Duke University did a very good study on the benefits of enclosed crawlspaces with directions and diagrams on best built practices. I have the bookmark on my work computer, I'll look for it tomorrow if you'd like. The flood zone designation also means, nothing in the crawlspace that can be damaged by flooding, so all the big HVAC duct work is in the attic (the unit is geothermal and in the spare bedroom closet). I really prefer the vents being in the ceilings anyway so it's good for us. We want to foam the attic ceiling and bring it into the house envelope also - but for now that is not in the budget so we had our installers use R-8 insulation and we double checked the mastic work behind them.

FYI, We just bought a house with the complete encapsulation package. While we live in Georgia which has a much higher ambient humidity than many areas in California, be aware that the humidity in the space will be high. You probably will need to install a humidifier system on top of the basic encapsulation. We had to do it as our humidity was above 70%. Our system included a spray on foam as well as the plastic sheeting. Understand that people answering your question may have a different system with different materials. Thus, the differences in cost.

Wise questions and encourage you to carve out the proper space for the HPWH. Most experts are not going to be ok with the pantry-door-open approach though it would probably perform fine if you actually left it open all the time. For noise, expect something like loud fridge. Plenty loud for most people to keep the pantry door closed, which could lead to problems. Yes, air in a room will be cooler and drier with HPWH, the smaller the more noticeable. I think AirTap's model is the only one that can be ducted at this time and don't know anything else about that brand. A smaller closet could work with homework and good HVAC craftsmanship. Conditioned crawlspaces and basements are ideal locations for HPWH. I feel if topography is suitable for a crawlspace, then you are approaching headroom necessary for HPWH. You could maybe dig an extra couple feet to create a pit for the appliance but would ensure the depression has adequate daylight drainage provisions. The extra cost of this work could be balanced by skipping the dehumidification needed for most basements and crawlspaces but it still might not be enough to totally eliminate conditioning needs. Electric demand water heaters can make sense in some situations but I don't think 23' is going to warrant them. You might be better off finding a plumber well versed in smart distribution design. I think homeruns (and close-to) of 3/8" or 1/2" tubing would be better in most situations. For those still in design stage, consider making small plumbing footprints a top priority.