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Discussion Starter #1
I just replaced some boiler parts, air vents, relief valve and an expansion tank. The tank was leaking and the relief valve was letting out some water. Replacing as I saw them and I understand what they are for, but not a plumber or hvac and don't know the design values.
My questions:
1. The boiler had Taco hy-vent near the boiler and Mist-0-maid auto vents at the ceiling level. My parents, mist-o-maid all over. Is there a difference between the two air vents? HY-vent looks more substantial, but that's about all I can see.


2. I did replace expansion tanks before. Just willy-nilly and monkey see monkey do. Just using the precharge. Just found out that there may be different tank for a boiler? I need to replace for my parents (about 30 yrs living in the house and never replaced as far as I know-previous work by a plumber but left no record). Should I pay about double for tanks that state boiler purpose? Is this same for water heater? The house has a whole house pressure reducer with a check valve. Pressure is set to 60psi and the water heater is 50 gal, gas.
 

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Expansion tanks for water heaters need to support 80 plus PSI and can also be used for boilers.

Expansion tanks for boilers need to support 40 PSI to give a safety margin over the rarely exceeded 30 PSI.

(More correctly the expansion tank needs to support a pressure higher than the pressure relief valve trip pressure.)

In each case preset the expansion tank to the normal hot system pressure prior to installation or with the system depressurized (cold for boiler, hot faucet open and water off for water heater.)
 
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Discussion Starter #3
I've got the whole house reduced to 60 psi. I finally found amtrol catalog stating the pressures and the temps. I should have got the amtrol. Watts, cheaper, but lower rates.


About the air vents, is there a difference between taco hy vents (image 1) and mist-o-maid auto vents (image 2)? In case uploading mixes the numbers, the brass cylinder is the mistomaid.
 

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