One thing to really watch out for with the hydronic, engine coolant heat exchanger type units is the water temps are often far hotter than you'd find in a domestic water heater and you're likely to scald yourself if you're not extremely careful. I'd recommend adding a tempering valve to keep the water temps in a reasonable range and prevent the risk of scalding.
This is spot on. I have been working Eric J. of the ABYC now for quite a while to get this addressed. It has supposedly been run up to committee and discussed and I am waiting to hear back from him.
The problem is much bigger than just hot water heaters getting to 180 degrees or higher. There are compounding issues of inadequate PVC hose max rated at 150 degrees being connected to 180 degree+ hot water heaters. When this happens the PVC hose can soften, bubble and burst or soften and deform enough to be blown right off a hose barb. The latter actually happened to us on a BRAND NEW 2005 vessel, in July of 2005, leaving us with no domestic water many miles from any source of it.
Scalding can begin at 140F and actual burns at 190F. An engine with a 180 degree t-stat running a slight restriction can EASILY get over 190F.
On more than one vessel I have seen 210F T&P valves blowing off on temp due to engines running hot doue to a bad t-stat, clogged intakes or restricted flow of raw water!! 210 degree water or an engine running at 210+ are 100% not acceptable and totally unsafe.
Residential plumbing has codes that prevent scalding hot water yet the marine industry has yet to address this when water is heated off an engine, perhaps because the builders don't want to pay an extra $20.00 for a tempering valve.
The water heater the OP bought is one of the few good ones that come standard with a tempering valve to limit scalding..
If you feel as strongly as I do about this dangerous issue, unregulated HOT water that can scald or burn adults or kids, or if you have been personally scalded or burned as I have, please voice your concerns to the ABYC and let them know this should be considered an UNACCEPTABLE practice..
IMO EVERY hot water heater that has the capability to be heated via a marine engine should be MANDATED to be sold with a tempering valve to regulate the hot water output temperature. HOPEFULLY the ABYC and the marine industry do the right thing, and YES I am an ABYC member..
Unregulated engine heated hot water heaters should have been banned LONG ago and SHAME on the companies who don't voluntarily include them as standard equipment as IsoTemp does!!!