when to skim new boiler?

Spunky424

just converted from oil to gas with a new boiler and hw heater. extremely happy about how quiet it is! wondering when is the best time to skim the boiler. i'm in NY and heating season is almost over. please advise on when the best time to skim the boiler would be. TIA.

STEAM DOCTOR

Anytime would be good.

Fred

If it can run a few cycles, you will wash any oils in new piping back into the boiler. I would run it a week or two, then skim. It is going to take a few skims to get all the oils out so anticipate having to do a skim a couple or three times next heating season as well.

STEAM DOCTOR

Agreed. Boiler needs to run for week or two.

Spunky424

appreciate all the quick replies. thanks so much! gives me time to install a valve on the skimming port.

Spunky424

So just skimmed the boiler for almost an hour and a half. I fired her up and got the water nice and hot before it started to steam. Then began skimming. The water was all clear but you could see remnants of oil on top of the water. How often and how long should skimming take?

Fred

Skimming has to be very slow, a trickle no larger in diameter than a pencil. Slower if possible. It may take a couple hours each skim and you may have to skim three or more times, at one or two week intervals (when the boiler is running often (during the heating season) to get all the oils out. It's the steam that washes the oil out of any new piping.

BobC

It took 5 skim sessions to get my boiler clean 6 years ago. The key is nice slow skimming so oils just float out of the skim port. I had the feed rate set so it took 90 minutes to fill a 5gal bucket.

Bob

Spunky424

BobC said:

It took 5 skim sessions to get my boiler clean 6 years ago. The key is nice slow skimming so oils just float out of the skim port. I had the feed rate set so it took 90 minutes to fill a 5gal bucket.

Bob

thanks for the reply. yea seeing as how the heating season is about to end. i'm going to skim probably one more time and then revisit this at the beginning of the next season.

Don_175

Before I skimmed our boiler, the water drop while the boiler was steaming. It would start about 2/3 the height of sight glass and would be about an inch from the bottom while running. It would then refill the sight glass relatively quickly after the boiler shut off. 

Now since skimming, the sight glass is at least 1/2 full while boiler is steaming. Doesn’t go down to the bottom anymore. The level will mostly fluctuate about ½” or so but every 10 seconds or so will drop a couple inches and recover. I do notice small droplets running down from the top of the sight glass inside. The water is very clear. Should I skim again or does it sound relatively normal? Thanks 

ethicalpaul

Good job! I’d skim that again. There must still be more splashing around in there than you’d like if water is splashing up to the top of the glass.

Don_175

Thanks Paul. Appreciate it. I skimmed again today for about 2 hours. Now, when boiler is making steam, water level typically fluctuates about 1/2 inch or so around water line stamped on jacket but every so often (maybe 10 seconds) it bounces down about an inch and a half for a second or so before returning. This is definitely better than before. I’m just not sure exactly what I should be seeing.

ethicalpaul

That sounds reasonable. You don’t want to see it dive to the bottom which would indicate water being carried out of the boiler. See my video below to see how oil in the water causes this:

https://youtu.be/jvt8qxBaRJU

Don_175

Wow! That was impressive! The level used to go way down, but after skimming, even when it drops that inch and a half, it never goes below halfway on the sight glass. Thanks again.

ethicalpaul

Your system will be much more predictable and able to be balanced now. Water in the mains causes all kinds of problems 

Don_175

So, I’m watching the sight glass and see the water level go up and down about ½ to ¾ inch but every 5-10 sec, it drops about 2” and instantly recovers. It never goes to the bottom like it used to. I’m thinking of skimming again. How long do you guys typically skim hour wise? I’ve done it twice. Each about 2 hours. Water was clear each time at the end. The first time I skimmed, I ran the boiler every 15 min or so until the stream coming out got a little frothy. The second time I skimmed, I didn’t run the boiler but kept checking the water temp of the stream. Even after 2 hours, it was still about 155 degrees. Any further tips? Thanks

mattmia2

Probably the biggest one is to let it run a week to a couple weeks between skimming. You probably got close to everything in the boiler but there was oil that got pushed in to the mains when it was surging. That oil will take some time to work its way back to the boiler as the steam and condensate wash it back in to the boiler.

Other tip is after you are done skimming heat the boiler until it steams to drive most of the oxygen out of the fresh water you just added.

Dan_NJ

I've probably skimmed 3-4 hours total over maybe three skimming sessions. I never had any froth in the stream coming out of the skim port. But I also didn't bother to turn on the burners at all - I would start when the water was still pretty hot and since my feed is from the hot water tank the new water would not knock down the temp as much. Of course it depends on how much junk is in there and I guess also how the section castings are made.

Don_175

Thanks guys. I skimmed a couple weeks ago so will do it again now. And i definitely run it after the skim to get rid of the oxygen.

SteamingatMohawk

Two points:
1. The first time new water boils all the oxygen in the water is released. The steam pushes out the air.
2. Every heating/cooldown cycle introduces "fresh air" into the system when the vent valves reopen.