Header For a Small Boiler

Drew2100

Hi Guys,

I understand why a bigger piped header slows down the velocity of the steam to drop out water. My question is that the SlantFin Galaxy recommends a 2.5" header in the manual which covers models from 100,000 to 300,000 btu's. Obviously, the 300 boiler pushes much more steam through the same diameter pipe than a 100.

My boiler is only 120,000 btu's. I'm coming off the boiler with a 2.5" riser that will be around 34" above normal water level. Would it be okay to reduce the drop header to 2" after the 2.5" riser on such a small boiler? The steam mains are 2". Reason being is a sprinkler contractor at work left a bunch of 2" Ward iron fittings and nipples after the job was finished last year. The equalizer will be 1.5" (Also my threader at work only goes to 2")

My old boiler was piped this way and seemed to work well. If I have to bite the bullet, I'll go 2.5" but if 2" is satisfactory that would save me some time and money.



Thanks.

JStar

Header

http://www.heatinghelp.com/forum-thread/146979/Steam-Formulas



Check out these quick reference guides that I made.



I would go 3" header. Most manufacturers recommend pipe sizes with a steam velocity of 35 ft/sec or greater. This is unnacceptable to me. Steam will be much dryer at 15-20 ft/sec.



You can also reduce the 2.5" to 2" at the boiler and use two risers. Then go into the 3" header.



The only way around it is to keep your pressure incredibly low. 8 ounces or less, and the 2.5" or 2" might be okay.

Drew2100

Single 2.5" supply connection

These SlantFin boilers only have a single 2.5" supply connection, but from reading here, they still seem to supply dry steam.



My old boiler had the pressuretrol set at 1.5# cutout, .5 cut in. Only seemed to cycle on the pressuretol during bitter cold weather.

JStar

Header

In that case, keep the 2.5" riser. You can by pre-cut and threaded nipples to make the riser connection. Two 12" nipples and a union should do it.

Drew2100

Already made 2.5" riser...

I already made the 2.5" riser from the boiler with two 2.5"x12" nipples and a union. I was then going to use a 2.5"x2" reducing ell and pipe the rest of the drop header in 2".

Burner input is 120,000 btuh and DOE steam output is 97,000 btuh, net I=B=R is only 73,000 btuh.

J Star, are your calculations on the DOE or I=B=R steam rating?



2" would be marginal for the drop header?

JStar

Header

They are for DOE output. The "problem" is that any size header will work, but will it work as well as possible? Dry steam costs a lot less to heat your home. Spending a few extra dollars now will save you a lot of extra dollars over the years.

vaporvac

Prior boiler: Atmospheric?

First a caveat...I'm no pro, just a homeowner who's become a bit obsessed with steam. You stated your old boiler was piped similarly and worked fine, but don't state if it was a wet-based boiler like the SF or an atmospheric one. I'm installing a SF Intrepid50 and the tech folks there are pretty adamant with the piping sizes.

I read a great article on HH a while ago (just spent an hour looking for it), that explained really well why you need to go bigger in the header with the wb boilers. My take-away was that the atmospherics could build a good head of steam IN the boiler, while the wb ones have a very high relative water line. Thus, the risers themselves act as a sort of steam chest. When producing steam they will suck the boiling/steaming water right out of the boiler and into the header. That means a  lot of water in the header  that requires a large diameter pipe to help it separate out and return via the equalizer. Otherwise, it could be sucked straight into the mains! That's also why, as I'm sure you already know, the equalizer shouldn't be reduced until after it turns downward. 



I wouldn't  imagine that bit of piping is a major cost in the overall project and most places seem to thread the pipe at little or no cost. Your new install seems like a great opportunity to get the best out of your new boiler.  To toy with the manufacturer's specs may end up being pennywise and pound foolish.

Btw, most of the SFs do only have one riser. The TR50 and up now have two, after SF realized they were producing wet steam with only one. All the more reason to go at LEAST three inches.

I hope that makes sense. If not, I'm sure the pros on here will set me straight. (At least I hope they do.) CTD