Air Vent height

brian_61

No. There's no air separator. If I was to get one of these, I have to install it in the pipe leading to the expansion tank?

brian_61

Air Vent Height


I hope a simple question for you. I have a hot water boiler that feeds the radiators in my house that I need to replace some parts on and remove a radiator and some excess piping from. My question is this, when replumbing the water in and water out (to the closed system), I understand that the air vents need to be at the highest point in the system, but do each of the air vents need to be equally as high as each other? At this point, each of the in and out piping is higher than the the top of the highest radiator and the furnace (although not the expansion tank), but the in piping is about 6" shorter than the hot water out piping. Should these be of equal height? Does it matter? And is it O.K. that the expansion tank is highest point on the system?

Steamhead (in transit)

Does your system

have an air separator? If so, and you're Pumping Away, that should be the only vent you need on the piping.

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Brad White

Air separator location and venting

The air separator ideally goes in the supply pipe leaving a boiler (hottest water releases most air). It does not go in the line leading to the expansion tank because that line does not see much of the air-bound water as exists in the mains. Some but hardly all.

This "hot main" location also should be, for other but similar reasons, on the suction side of your circulator (lower pressure than on the discharge).

This should also be the place where the expansion tank is connected, the principle criteria being that it is on the suction side of your circulator. Always.

You will notice that most air separators have a tapping for convenient installation of the expansion tank for this reason.

If you do not already have an air separator AND you are pumping away from your expansion tank, you can get away without one IF you get the air out in the first place and vent it again after bringing the water to the highest temperature.

Back to your original venting question on vents: So long as the vents represent the high point of that particular branch, they do not all have to be at the same height.

If for some reason you do NOT have vents (say a baseboard system with continuous small diameter tubing) you will have to purge the system branch by branch, forcing in water at a high velocity to carry gross air along with it, out a low drain valve. This should remove 95-99% of the air but it may have to be repeated once the system is heated to limit.

If you have cast iron standing radiators rather than baseboard, purging is a challenge as the velocities in the cast iron radiators is insufficient to carry out the air. Fortunately, they should have vents already.

Vent each and go forth. Keep the pressure at the top of the system at not less than 4 PSI at that point to give yourself some residual force to keep air bubbles moving to the vent and to keep them smaller.

brian_61

thanks and one other thing

Thanks for the info. I have cast iron radiators for the heat and, yes, have much experience with purging the air from them. Since I've purged all the water from the system and had the boiler off for much of the summer, are there particular steps I should take before/during refilling and relighting the system? Other than purging the air? I've attached a picture of the beast before I started reconfiguring and removed the upper most piping that went across the room to an old radiator.

Brad White

I cannot see

what the relationship is between the circulator and the expansion tank. If not "pumping away", start there and make sure it is doing so. It is less important where the circulators are (inlet of boiler or outlet of boiler) so long as the expansion tank is on the circulator inlets. In other words, move the expansion tank connection point to the inlet of the circulator(s) if that is easier for you.

Once a system is full, vented and with enough pressure to keep about 4 psi at least at the top, you should not need to do anything.

If you find you have developed an air problem over the summer, I suspect a leak or other problems.

brian_61

thanks

Thanks for all the info. Very much appreciated.