In yesterday’s inspection, there was an object mounted on the cold water supply line - white, globe shaped
Can anyone tell me what this is?
Maybe some type of pressure relief?
The schraeder on top makes me think that’s an older auto-bleeder, but I am confounded why its on a water heater. I know that in real small cottages they use a water heater, at a reduced pressure, to provide the hydronic heat for the dwelling. Was this water heater being used for domestic hot water or hydronic heating?
You sure that’s a domestic water heater?
Was there a circulating pump?
Looks more like a home brewed hydronic heat boiler by the looks of the extra valves and that air chamber that you ask about.
One thing to look for on these type of systems is the relief setting on the “TPR” valve which will be pressure only @ 30 PSI, no temperature pop off.
They sure have that TPR valve way up there.
I’ve made a few hydronic heat systems for small areas like hot tub additions using regular water heaters.
Its a water hammer arester.
Then what is the schraeder on top for? Is it some sort of bladder type watter hammer arrestor?
BTW, “Drawing” a TPR discharge pipe on the wall does not function nearly as well as having the actual pipe 
here is couple more -
http://www.accentshopping.com/product~VN~Hose_Bib_Water_Hammer_Arrestor_3%2F4_Hose~P_ID~152354.asp
I am particularly impressed with the quality of the plumbing and the “thermal blanket” on top the tank. Wonder how much that is saving them in energy dollars? May as well be a beer coaster up there.
The thermal blanket on top was the temporary residence of a long tailed critter, he left evidence 
There were two TPR valves. One one the hot water piping, and another on top of the unit, piped with 3/8 copper tubing. Someone tried, just didnt’ have it together.