@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.

Lots of different ways this could go, IMO. Yes, mold testing is likely to be inconclusive, as is is EVERYWHERE in our environment. The worse-case scenario is that a mold bloom couls occur, covering much of the wood, and be quite expensive to eradicate. What I would do...and this is from a non-professional, and is off the top of my head: I would have an INDENPENDENT inspector look at the place. Spend a little bit of time over at inspectionnews.net where in my opinion the best inspectors hang out. Heck, most of the pros over there will answer questions from homeowners. One of them may be in your area. Depending on the answers you receive, and what your inspector says, I'd have the seller escrow an amount that would cover remediation if bad things occur within a reasonable time frame, say a year. That way, if it is nothing, as they believe, they will get back their money. And if it does, you'd be made whole. When you propose this, you'll quickly be able to find out if they're being truthful about their opinion of "no problem." Don't know the climate of your location. It sure would be good to open any foundation vents to get some cross ventilation...but in December that could be problematic. At the very least a GOOD dehumidifier....they make crawl space models...about $800-1000...not the HD / Lowe's models should be installed immediately. Merry Christmas! Rod

My Rinnai gas tankless water heater has a built in recirculation feature. My furthest bathroom is 50' from the tankless. The shower is hot within 8secs of turning it on. My recirculation pump is on a timer and is programmed based on my family behavior. I was really concerned after reading so many of the reviews online about tankless water heaters topics like temp sandwich and not being able to use multiple showers and appliances at the same time. I have low flow shower heads in my bathrooms from Grohe and Hansgrohe. Two of my bathrooms have thermostatic valves. The third has a very old pressure balance valve that will be replaced soon. The shower heads are rated at 2.5gpm. They perform really well. The tankless also has a feature to fill a bathtub,. I have used this once and the tankless worked like a champ and filled a 50gal tub in 9 mins. I have city water and will perform my first flush of the system in May. I was also afraid of the temperature drops as it got colder. We had a week of sub zero temps and I noticed no impact on the water heater. We can take two showers concurrently, run the dishwasher, washer and a faucet at the same time. My home has a crawl space and most of my plumbing runs through the crawl. The tankless unit is hanging on the wall in the utilities room. Just wanted to post another experience in tankless. One of the main drivers for going with tankless in my case was that I needed the space. The tank heater blocked access into the utility room and a wall needed to be taken down to remove the heater. I have a Rinnai RUR98i. Good luck!

ionized_gw: I think that gas tankless has become more mainstream. In addition, the incentives have started to go away. Much of the initial complaints with gas tankless were around bad installation and/or bad retrofitting. I don't think they are sliding in popularity as much as they simply aren't the new kid on the block any longer. On new installs, gas tankless doesn't cost significantly more than a power vent heater and you see them installed on new upscale homes here because of the unlimited hot water. Rheem has addressed the "cold water sandwich" by delaying a "post purge" cycle when the heater is turning off and on frequently. This means that the heat exchanger doesn't rapidly cool off -- eliminating the "cold" part of the sandwich. I insulate my hot water lines also to reduce heat loss between uses. I know I'd never go back to a standard tank water heater. As for electrical requirements on the hybrids - it's the same as a standard electric water heater. The reason is because they sometimes have to fall back to electric resistance heat if the ambient temp is too low or quick recovery is needed. There was some reliability issues on the early hybrids that has since been worked out, I believe. As a side note: Hybrids are being linked up with PV -- meaning that while you would never use solar PV to power electric resistance water heater, it's a good match up for a hybrid water heater. Oil isn't much of "a thing" where I am, so I can't really comment on that. SaltiDawg: The op was seen screaming and running from the building