How does air get in my system?

Darren_6

Hi All:

Stupid question from a homeowner, but, every winter/fall I bleed the air from the cast iron radiators in my home. Thing I have never figured out is.....How did it get in there in the first place??...

and how do I determine if the make-up to the system is working properly???...

and..while I have your attention..how do i tell if my boiler (gas fired Burnham from the early 80's) has a vent damper on it? (what does it look like? where would it be situated)And if it doesn't have a vent damper on it, would I be well advised to put one on ? (for energy savings?)

thats probably enough dumb questions for one heating season.

Thanks in advance

Darren

Ken_8

That depends...

The reason you have to bleed every year is because:

1) the citculator is sucking the water through the system instead of pushing it.

2) the expansion tank is non-bladder type and allows air to escape and get back into the water.

The way to be sure the "make-up" is okay is to check the pressure gage. If it's around 12 p.s.i. when cool - and around 20 when fully heating, it's in the ball-park.

If you have a stack damper it will reduce fuel use by about 9 %. If however the model you have does not have the inherent ability to use one, the cost to change all the controls and gas valve to install one would be nearly prohibitive.

We love questions.

Keep 'em coming.

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Walt Deacon

Air gets sucked in

Remember the trick of collapsing a maple syrup can by heating it, then throwing it out in the snow? The steam system works the same way when it cools off. Pure steam will collapse to a pressure about 7 psi below atmospheric when the system cools to 80 degrees. Vents, vacuum breakers, and leaks let air in to equalize the pressure, so that it's full of air by fall when you start up!

Mike T., Swampeast MO

Bell & Gosset Air-Trol

Assuming you have your original big, plain expansion tank.

Install (or have one installed) and the problem will disappear.

Gravity circulation allows air in the tank to migrate to the system. The Air-Trol stops this before it can happen.

Aidan (UK)

Air(?) in the radiators

Also, (assuming it's a hot water heating system) it may be hydrogen, the product of electrolysis. This can happen due to galvanic/bi-mettalic corrosion between copper components and iron/ steel radiators and boilers. The way to tell is to bleed the radiators whilst holding a can inverted over the vent. If it is hydrogen it will rise into the can and will ignite and burn with a 'pop' when lit.

There is also oxygen produced by galvanic corrosion but you don't have to bleed this because it combines with the iron to form rust.

If it is galvanic corrosion, the cure is to dose the system with corrosion inhibitors, which inhibit it.

Plumbob

I assume you have a hot water system, not steam. Unfortunately, in the US, most people in the early '80s (and many contractors even now) didn't have a clue about hot water heat.

In our newly aquired system, (a) we are Pumping Away from the expansion tank, which means air is not as easily sucked into the system; (b) we have a new expansion tank in which the water is separated from the air by a membrane, so it can't absorb the air and carry it to your radiators; (c) we have a good air eliminator. We don't have air problems any more.

Re the vent damper, you don't have one (sticking my neck out here, but I bet I'm right). It's not worth the trouble and expense and risk of retrofitting the system...if it doesn't open when it should, you'll have CO in the house. I suggest saving up for a modern and properly installed new system, which (with the addition of outdoor reset) will give you increased comfort and decreased noise, not just energy savings.