Early vs Mid vs late in heating cycle

Don_175

Trying to track down some water hammer causes. I was reading Dan’s article of early vs late in heating cycle. Would early be when steam is just starting to fill pipes etc? We get water hammer just before radiators start to feel warm. Maybe 10 minutes after boiler starts

Jamie Hall

That's early. Check all the runouts to the radiators for lengths which aren't pitched back to the main adequately.

ethicalpaul

To expand on this a bit: you are looking for places where the pipe pitch is allowing water to collect. After a steam cycle, all the water should drain back to the boiler. If there are any sags or collection areas, the water there will cool.

Then at the start of the next cycle, the steam will come in contact with that cold water and collapse (condense) rapidly which causes a shock that throws the water against the pipes (water hammer).

After some minutes, that cold water will be heated up by the steam and the reaction will no longer occur until the next cycle. So the reduction of the noise as the cycle continues is a sign of this occurring.

Don_175

Thanks. If it were dirty water in boiler, would it only bang for a short time early in the cycle too, or would it continue throughout?

ethicalpaul

it sounds like you are saying "dirty water, causing carryover of boiler water into the steam mains."

First, be careful of using "dirty water". It is really too general of a term. Lots of boilers with water that looks dirty are fine. Lots of boilers with perfectly clean pristine drinkable water carry over like crazy.

If (for various possible reasons) your boiler is carrying water into the steam mains (often called "wet steam", depending), then yes, all kinds of problems including all kinds of sounds can result, at various times in the heating cycle. Basically it's such a bad situation that all bets are off.

Don_175

Yes. I guess I was referring to wet steam. We only get noise at the beginning of the heat cycle. Never any other time. 

ethicalpaul

Then barring any other information, I would say you have one or more places where condensed water is resting, as Jamie described.

What you are describing doesn't sound like boiler water being carried into your steam pipes.

Don_175

All this makes sense, but what would make it vary from day to day? Today it ran, and no noise. Last night it sounded like we had an army of chimps with sledgehammers banging on the pipes

Don_175

Any ideas why some times it's noisy and other times not?

ethicalpaul

To be able to say for sure I'd have to probably be there to experience the sound and location and timing myself. But here are my thoughts:

- perhaps there is carryover after all that is occurring only under certain conditions
- If there is standing condensate water somewhere, the temperature of it definitely matters. So after a long time without a call for heat, I would expect the hammer to be greater at those times. The weather would affect this as well (fewer calls for heat when it's warmer)

Don_175

I had read that slow venting is the way to go with radiators and that fast venting could contribute to hammer. All pipes look like they are sloped appropriately. Could too fast venting on mains contribute to water hammer if high velocity steam were to meet condensate in main?

Jamie Hall

Wandering out a fair distance on a limb here, but... no, too fast venting on a main will not contribute to water hammer in the main, unless the main is not pitched correctly. And if the main is not pitched correctly, no manner of venting will make much difference.

What may make it worse, however, is lack of insulation on the mains.

Condensate, particularly on startup, is pooling somewhere and getting carried along. You need to find the low spots and fix them.

Don_175

Thanks very much. Will check it out

Don_175

So I checked all pipes in basement especially right where it sounds the loudest. All are pitched appropriately and well insulated. I notice the banging occurs right before the radiators start with their expansion sounds. If the system is already hot, we are talking about 10 minutes in. If the system has been off a while, it’s more like 15 minutes before the banging occurs. It typically lasts about 10-20 seconds. Boiler typically turns off on thermostat being satisfied around 30 min after starting up. Would the timing still be considered early in this scenario?

Jamie Hall

That's definitely early. One is thinking in terms of what is happening when the steam first gets there -- that's early. If it's during the cycle, things nice and hot -- mid. At the end -- boiler shuts down -- late.

Early is almost always (not always!) due to the condensate forming in the steam mains and risers as they are heating up being able to pool somewhere -- the bottom of a riser is a favourite location -- and getting banged around by the oncoming steam. Once things heat up, there's very little condensate in the mains or risers (except in one pipe steam -- which still have to cope with the radiator condensate and can just keep on clanging away_). Insulation. Check pitches. Grin and bear it?

Don_175

Definitely one pipe. Only bangs for that short time. Thinking about grinning and bearing it!!! If it did it throughout it would be a different story 

Don_175

So here is a weird turn of events. We’ve been having the banging 10-15 minutes into the heating cycle all season. This weekend I turned down the vent on one of our radiators where I can sometimes hear something like boiling water. It is a Castray. I put a level on it, and it is tipped slightly away from supply pipe. I tried to lift the end a bit but can’t. I turned the vent from 6 to about 4. I have not heard the loud banging since (or the boiling water sound). The only thing I notice is a more subtle sound like a small thump that only happens once or twice at around 5 minutes into the heating cycle. The previous noise was a loud metallic banging that lasted about 20-30 seconds. Could this possibly be the fix? Or is it just a coincidence and noise will recur later in season?

neilc

sounds like you slowed down your steam entering,
and are allowing your condensate a more relaxed return,
and without the violence between the 2, peace on earth,

try again with a lever, or garden shovel, to raise your vent end,
try little peices of plastic milk jug under the rad legs as "slips",
the dull thuds might be expansion movements, the rad feet, or the pipe thru the floor or wall,
try plastic around the pipe thru the floor also if there's a tight rub there,

post a picture of the rad

EBEBRATT-Ed

@Don_175

Yes. You have water laying in that radiator or in the pipe feeding it. It's usually always a pitch issue. a 2 x 4 and some blocks will get the end of the radiator and some shims and a level are the fix. Slowing the venting like you did is ok if you get enough heat out of it and can stand the thumping

Don_175

I put a couple blocks of wood on the floor near the vent end and used a pry bar to lift the radiator. I was able to slide a piece of ceramic tile under it. But it won’t lift up much. The level still shows it’s tipped toward the vent. We have had no more banging. It heats well. This morning I did hear a slight rumbling sound in bathroom. It sounds like an old coffee pot. The thing that still confuses me is if this radiator were the culprit (as we have no more noise lately), it is located on the second floor, but the noise was in the basement. I never heard the banging near this radiator. Only the boiling water sound.

Jamie Hall

That's why water hammer is such a nuisance. In this particular instance, though, you may have managed to raise the whole riser assembly enough to correct a problem in the basement.

Don_175

yeah. It’s weird. The first thing I did was turn the vent down 2 notches, and the noises stopped. Then I raised the vent end of radiator slightly (but as much as I could). I’m wondering if this is just a coincidence and something else changed to stop the noise. 

We had an 8 degree setback at night, which I decreased to 4 around the same time. 

During the day, our heat is set for 68 and boiler comes on at 66.5. That has not changed, and noise was happening throughout the day. 

Don_175

So I went around and put a level on each radiator. A few were tipped toward the vent. I put a couple nickels under the legs near the vent. Someone mentioned a degree or two of tilt toward the valve is all that’s needed. If the bubble is still between the lines but touching the far line on the level, is that enough tilt?

EBEBRATT-Ed

@Don_175

depends o the length of the rad, how fast or slow it vents etc. Trial and error. As long as it's quiet that all that matters