Hi all. We have a water system, Burnham Series 2 heater, 18 cast-iron radiators, 5 of which are on the third floor, which we use for storage only. This winter, one of the radiators on the third floor remained cold. That suited me well, since we don't need heat there. But I wanted to know what was going on. Just opening the bleeder on that radiator didn't do anything: no air was coming out. So I checked the pressure in the system. About 12 PSI. I raised it to about 18, opened the bleeder again, and guess what, the radiator kicked into action. Good.

But that made me think: how about LOWERING the pressure again, perhaps to about 8-10 PSI, to keep ALL the third-floor radiators cold? Most of the radiator valves in the house are non-functional. One plumber I asked about replacing the valves told me he wouldn't touch these old pipes. Surely I could find one who would, but that's not on top of my priority list. Our first two winters in the house, I covered the third-floor radiators with jackets I made out of aluminum bubble-wrap insulation. Would be more effective to lower the pressure in the system. Any reason NOT to do this?

Thanks, EB

if you raised your pressure enough to get water at the top floor radiator vents and then lowered the pressure, you would still get heat from those radiators because they are full of water.
you would have to lower the pressure, drain some water from the system, open the vents upstairs to let the radiators drain down and then close the vents.
what happens is the pressure fills the system and the circulator moves the water around.

I get it. Just to be sure: having radiators and piping full off air instead of water on a permanent basis won't cause them to rust or anything like that?

won't hurt a thing...
unless you introduce oxygen into the system, rust (iron oxide) can not form.

They are proposing adding air, by draining.

Yes, the air that will come in when I drain the system and stay there permanently was exactly my concern. On the other hand, it's just a finite amount of oxygen that will go in, and it will not be renewed. So perhaps I shouldn't be concerned…? EB

exactly...
once the oxygen is used up, it must be replenished in order to create more rust...

Of course they will rust. They are black steel and cast iron.

The air introduced to allow the system to drain down DOES have oxygen in it.

it does have oxygen but no where near enough to cause even a modicum of rust.

I would tend to agree with Packy. I started draining the top-floor part of the system…

Here's another question though. These radiators have both supply and return pipes at the bottom. I take it that I need to drain them completely in order to stop the flow of hot water in them. In other words, draining just a few inches won't do much, since the water will continue to flow in and out. Is this correct?

correct again..
unless you really, really want no heat upstairs, a couple of inches of water in the radiator will give you a small amount of heat and keep things from freezing.
it will be pretty hard to tell just how high up the pipes the pressure is sending the water.
whatever you do, don't open the vents on the top floor radiators. the compressed air in the radiators will help keep the water from rising into them.

Got it. Thanks.

Hopefully you don't have plaster walls up there, or it will become, only suitable for storage.

quote; it will be pretty hard to tell just how high up the pipes the pressure is sending the water.

If the pressure gauge is a "tridicator" it has a 'height gauge' with the pressure gauge to show how high the water is in the piping. What "compressed air" is in the radiators? He bled the air out.

i advised him to (after draining down) not bleed the top floor radiators upon refilling.
as for the tridicator, you have a good point. i never thought of that..

I did use the height gauge, sort of. I have a sense it's not the most precise of devices. Here's what I did: I shut off the inlet valve and turned down the thermostat; drained some water from the system, went upstairs and opened all the radiator bleeders; drained a larger amount, bringing the pressure to about 20 feet of water; went upstairs and closed all the bleeders; opened the inlet valve and lowered the setting of the Watts pressure regulator to about the same pressure as I had reached in the heater at that point (holding the inlet pipe with my hand and listening carefully, I could tell when the water would stop flowing in); increased the thermostat setting again and after ten minutes checked that all radiators on the second floor were warm and had no air in them, and all radiators on the third were cold, which was indeed the case. It worked! Thanks to everybody for your advice. It will save us some money... and no doubt reduce the carbon footprint of the state of RI quite significantly

Paul, thanks for alerting me to this. Do you think cold temps -- I won't let them drop below 40 deg F -- could be more damaging to plaster walls than warm ones, about 90 deg F on the third floor in hot summer days, and than humidity -- easily 80% RH on humid summer days? Indeed all the walls on the third are horsehair plaster, and there are quite a few good cracks too, which obviously have been there for years. Previous owner patched up the most conspicuous cracks before putting the house on the market, and did a rather poor job of it. All of this will be taken care of in due time, and I was thinking that for the time being letting the temps drop to about 40 F couldn't hurt… If you think otherwise, do tell. Thanks.

I think you might find large sections of the plaster will fall off the walls. The plaster walls do not stand extremes well. Hot and humid is probably better than cold and dry. Look at the structure, as a whole. If you let the 3rd floor get down to 40 degrees, you then have an unconditioned, uninsulated space over your "bedrooms"? What type of heat...gas or oil? Are the valves for those radiators stuck?

quote; I have a sense it's not the most precise of devices.

Actually it is VERY precise because it uses a "standard" of physics, namely the weight of water, so if your pressure gauge is accurate the height gauge will be also.

quote: if your pressure gauge is accurate the height gauge will be also.

Isn't that a big if? How precise and how well calibrated are these mechanical pressure gauges, which use a so-called Bourdon tube? The one in my Burnham heater looks pretty flimsy to me. Also, the resolution in the low range is poor, since the range is 0 to 75 PSI = 173 feet H2O. Just the needle width is about the equivalent of 2 to 3 feet H2O on the dial. By the way, from the markings on the dial, it seems that the device is non-linear in the low range, contradicting Wikipedia on this topic. Big surprise!

Your mentioning of the physics of manometers got me dreaming about a mercury pressure gauge that one could rig up to get a high-res measurement of the pressure in a heating system for a three-story house. All it would take is a glass tube in the shape of a U, open on both ends, enough mercury to fill it, and a few fittings. In order to measure pressures of up to 20 PSI one would need a U less than 4' high. Wouldn't that be completely cool?

quote: I think you might find large sections of the plaster will fall off the walls.

Hmm, would rather avoid that.

quote: If you let the 3rd floor get down to 40 degrees, you then have an unconditioned, uninsulated space over your "bedrooms"?

Yes and no, there is half-decent insulation in the walls and ceiling of the third floor. On the other hand, cellulose insulation was blown in between the 2nd and 3rd floors. This was done in the 70's: when I fixed one of the "plugs" they had made in the floor of the third before I refinished that floor, I found a piece of the local newspaper from that era on top of the cellulose. Another piece of info is from the "history sheet" written by previous owner. It says: "June 2007, third floor heat was reconnected. June 2009, Oil boiler was removed and new gas burner system was installed." Putting the detective work together, my guess is that the third floor was likely left in the cold for four decades, from the 70's to about 2009. If so, and considering what you say, the damage caused in the past by the cold is relatively minor, and I would think that no more damage will result at this point from keeping the third floor cold.

quote: What type of heat...gas or oil? Are the valves for those radiators stuck?

Gas. Valves are either stuck or the head is turning in void and not doing anything. I was thinking of installing thermostatic valves. These valves have been in standard use in Europe for a good thirty years. I am from France. When I had central heating installed in my house near Paris in 1985, the plumber installed thermostatic valves without even asking me. The heater was a natural-gas heater, which did both heating and hot water. Had a system bypass to let the circulator do its thing when the thermostatic valves would be closed. Worked remarkably well. Any opinion on thermostatic valves? Do you foresee any problem installing them on old cast iron radiators with black iron piping and fittings that have been painted over a million times?

TRV's are great, and wouldn't hesitate putting them on a system plumbed with copper or pex. The problem with multi-floor 100 year old houses, is, many sit on rubblestone and brick foundations and the settling is excessive. Often when you disconnect a radiator on one of those systems, the pipes go BOING.This leaves you wrestling 100 year old iron pipes, trying to reconnect the sprung piping. This usually causes leaks elsewhere in the system. Sometimes, the leaks are a good distance away, and Mr. Murphy says they will be in a wall, in an inaccessible place.
There can also be a challenge finding a TRV that fits the distance between where the vertical riser ends to the horizontal connection at the radiator.At best, this is another wrestling match.
I hate to come off gloom and doom, and I'm sure you could find a young plumber, that would say it was no problem.I believe you said a plumber told you he wouldn't touch the pipes?....He was a smart man.

Yup, the guy who installed my mini-split AC units said he wouldn't touch the radiators for exactly the reason you said. He's a good guy in his late 60's with plenty of experience, but he does specialize in AC and I was wondering whether he just was not interested in this kind of job. So I got it now. Thanks for the advice.

I am 80, and I would have no problem "touching those valves". Someone is overly pessimistic about what would happen when the valves are disconnected and the problems reconnecting them.

Where would you get the mercury, unless I sold it to you?

I would get it from my dentist, who happily puts "silver amalgams", in people's mouths (not mine). Just kidding. I wouldn't want any of that stuff in my house.

Specifically, what my AC guy said when he looked at the radiators was that he would have to use force and the black iron pipes might deform...

Someone is not being pessimistic. Someone is being reallistic. It's easy, when someone is gambling with someone elses money.

That would be a factor with a steam system, but seldom, if ever, with a hot water one.

And I am being 'realistic' based on may years of working with old steam and hot water radiations systems, and seldom encountering the 'problems' you describe. In any case, the end result is what counts and therefore I would do whatever was necessary to accommodate the customer's desires.