I beg to differ on your explanation that electrolysis does not cause calcium buildup, it most certainly does. Calcium buildup is caused by minirals in the water, especially hard water, and further exacerbated if ANY voltage is present (a short/arc ) in LWCO, temp sensor, heat timer, even low voltage stat...milliamp included.
I've installed hundreds of boilers and hot water tanks because dielectric fittings were not used, most plmbers wont use it because of expense, you said you are a home inspector how many retrofits have you inspected? So saying that dielectric fittings are required when working on 2 different metals, answer me this, how many people even KNOW about dielectric fittings? Let alone use it. I've taken apart thousands of pipe...galvanized steel, copper, black pipe, schedule 40&80... and they all display the same thing heavy buildup of calcium (miniral deposit).
The reason you have buildup on the outside is sweat or a tiny leak caused by electrolosys so the use of a dielectric fitting is a must for a job done right. I agree the reason most HWT have a 5-7 year lifespan is because you have fly by night wanna be plumbers installing HWT, or just everyday folks who own a home and in need to replace a tank, you will never see a master plumber install a tank without that fitting. I did my own tank with that fitting 15 years ago, as long as you do a PM (blow down the tank and boiler you're golden).
I also never said calcium causes blisters, I did say it could be anthing.
I'm not a Dr. So I don't know.
I use "Stay brite" on all my fittings none of that 50-50 or 60-40 crap. Check out the holding strength of all 3.
And heat pumps are all over the north east I have a split system unit what do you have? Incramental, wall or transom? It does make a difference on BTU/hour output.
I also have hard water (well water) but I put in a water softener (water boss). It goes through 2 different units sand filter and then finally a softener salt pellets from home depot, lowes.
B4L