The log house I'm building will have a propane tankless water heater (Rheem). Can these be installed in a crawl space? It would certainly simplify things if it could. The crawl space is 4 feet high.
1) Some manufacturers recommend/require a backdraft damper if you are installing in a freezing climate, this is especially important if there is only a short run to the exterior.
2) There's a lot of electronics and other assorted moisture sensitive componets in these heaters, if this crawlspace is "damp", I'd be leery of installing a tankless unit down there, in my Chicago climate I frequently see corroded equipment in crawl spaces, and it's often equipment such as conventional tank type water heaters much less sensitive than tankless units.
3) I've put together a webpage on my experience with tankless units (I like them, but they are intolerant of incorrect installation), you may find it useful:
A forum community dedicated to Do it yourself-ers and home improvement enthusiasts. Come join the discussion about tools, projects, builds, styles, scales, reviews, accessories, classifieds, and more! Helping You to Do It Yourself!