Hot Boiler Water, Cold Makeup Water.

Boots · Post by **Boots** » Tue. Dec. 11, 2012 5:00 pm

Is it ok to purge air from my boilers while they are up to temp (180°-190°). The reason I ask is because of the cold makeup water being introduced as the pressure drops.

LsFarm · Post by **LsFarm** » Tue. Dec. 11, 2012 8:58 pm

If the boiler vessel is cast iron, and you vent a large amount of air, then yes you could possibly thermal-shock the iron with the cool makup water.

It is very unlikely that you could heat stress a steel boiler vessel.

Does the makup water feed directly into the boiler vessel or into supply or return piping?

Greg L

Sting · Post by **Sting** » Tue. Dec. 11, 2012 10:54 pm

I might be more concerned about your safety ---- have you done this before?
Are you prepared for the venting of scalding liquid and the subsequent vapor cloud - the hot wet air in the boiler room or basement

Boots · Post by **Boots** » Wed. Dec. 12, 2012 4:07 pm

LS,

The make up water does feed directly into my cast iron oil fired boiler.

Sting,

short answer, Yes.

I have drained my boiler when hot before. And have done some purging. I have hose bib drain valves the I purge the air from, and I have a heavy duty hose with "water hose" ends that I place the discharge end of into a bucket. I have done this cold a few times, and purged a lot of air from the system. and I have done it hot only a hand full of times, but do not normally get enough air out that it needs to displace it with makeup water.

Last night I noticed that I could hear air bubbles as the main circulator ran. when the house was up to temp I decided to purge the air. I got enough air/water out that it dropped the pressure enough to allow makeup water to flow. I stopped purging the instant I heard it. I figured that it could cause an issue, but wanted to be sure.

Sting · Post by **Sting** » Wed. Dec. 12, 2012 5:37 pm

good

now - when you introduce new water with this purging - you will/may also be stuffing in new air -- its in the new water

so a better plan may be to shut the system off on a calm day about noon - let the water sit and let the air get to the top of the system where the bleeders can let it out.

if you don't have bleeders - well then you still need to let the trapped air congregate by leaving the system off for a while -- then you can blow it out all at once

but -- It Depends

Kind Regards
Sting

Boots · Post by **Boots** » Wed. Dec. 12, 2012 6:04 pm

thank you for the reply,advice, and tips. I need to plan a shut down to make a few other repairs as well. I guess I need to get on the ball.