Purging Air From Hydronic System?

Old 09-21-10, 04:33 PM
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Purging Air From Hydronic System?

I have a residential system that is comprised of a boiler that serves:

1. Five Zones of Radiant Heat
2. DHW
3. Two Zones of Baseboard

Glycol in system.

Have a leak in the TACO Circulator that is on radiant heat loop.

There is a big boiler loop that injects hot glycol into the radiant heat loop.

I will have to drain part of the boiler loop to change the circulator O-Ring (the boiler loop runs about 2' feet above the radiant heat loop). I will also do the cartridge at the same time. So I expect to get quite a bit of air in the boiler loop (about 8 feet of pipe) and also between the supply manifold and the 5 individual shutoff vavles for the zones (about 3" of pipe for each zone).

I have a SpiroVent on the radiant supply manifold and air vents on top of the expansion tank and DHW tank.

I am presuming that I can't get the air out of the system with just the vents, so I plan to use a utility pump.

The plan is to first purge the main boiler loop by tying the pump output to the supply side of the boiler loop (above a shutoff valve) and tying a hose from the return side of the boiler loop to a bucket of glycol mix.

Then going onto the radiant heat manifolds and purging each zone.

1. I am looking for feedback to see if this makes sense?

2. On the boiler return, can I go on the input side of the boiler return (before it goes into the boiler), or should I pump through the boiler and tie on the supply side of the boiler (between the boiler and the shutoff valve mentioned above)?

Thanks FJ
Old 09-25-10, 01:15 PM
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Before refilling the boiler, I would install shutoff valves on each side of the pump for maintenance. You are now finding out the aggrevation of servicing a wet-rotor pump combined with glycol.

Normally, I'd just refill the system with water, fire up the boiler, and find out which heat emitters don't get hot - using the boiler's pressure to purge air, if required. But, with glycol, I'm not sure what the best approach is.

Do you have air bleeders on the various heat emitters? That would be ideal.

You said that you have an air vent on top of the expansion tank? I assume this is a bladder-type tank (looks like R2-D2). Normally there is a schraeder valve on top for pumping up the bladder's air-side, but not an air vent. [Do NOT remove air from the schrader valve]

(By the way, while your system is depressurized, pump up the bladder to about 12-15 psi - for a 2-storey house and a basement. This can NOT be done after the system is pressurized, [you will NOT get an accurate charge.])

I assume that your house is regularly unattended during frigid weather - and therefore the need for antifreeze? Glycol is a real pain - it's messy and awkward to drain or fill. It is toxic and can carry less heat that water. For new house construction, I think I'd go with forced-air heat before having to use glycol with a hot-water system.

Last edited by NJT; 09-25-10 at 06:39 PM. Reason: "This can can't be done" was what Mike sed! huh?

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