Need hot water from boiler room/Watts 530c psi

[John Z]

My boiler is in the garage, which is where I do a lot work and sometime require a couple of gallons of hot water. I would like to be able to get the hot water directly from the boiler. The boiler supplies both heating and household hot water. It has an expansion tank.
1. Can I open the pressure relief valve and get water from its drain pipe?
2.If not, where is the best place to tap in and install an garden hose valve? The hot water line from boiler to house?
3. The hot water supple line from boiler to the house has a adjustable (calibrated) pressure relief valve (photo). It is dripping very slowly. I am planning to replace it with a Watts 530c (1/2"). What psi should I set it to?

Thanks in advance!

 

[Fitter30]

Heating hot water boilers do not like fresh water entering them. Fresh water brings in oxygen which has to gotten rid of and you will shorten its life. Purchase a 5 gallon electric w.h. would be better but if you insist put a valve in line and don't keep adjusting the relief valve it will fail.

 

[Sponsor]

 

[John Z]

"Heating hot water boilers do not like fresh water entering them."

Doesn't fresh water enter the boiler every time I take a shower or do the dishes? (I probably should have mentioned that I do not have a hot water tank for house hot water use. It's just the boiler; that's it)

 

[Fitter30]

Take a couple pic of it. Normally a boiler is used for heat not for domestic hot water.

 

[John Z]

Boiler is all there is in the house - no separate hot water tank.
In the pics: arrow points to outgoing domestic hot water. Circled is the leaking adjustable pressure relief valve. I am planning to replace it with a Watts 530c (range: 50-175 psi) . My question is: what psi should I set it? (the one that is on the boiler is so old that I cannot see the markings).
Thanks.

 

[Fitter30]

Relief valve 125lb max. Could pull the relief valve install a brass nipple and tee screw the relief in one side a 3/4" boiler drain valve in the other side. Your domestic hot water is called a tankless coil in boiler.
https://www.supplyhouse.com/Bluefin-BDM075-3-4-MPT-Boiler-Drain-Male-Threaded-Lead-Free