Can a drop header drop too far?

TomM

installing this now, should have done in summer, avoiding a divorce.  :-)



my boiler risers are 24", (2" to 2.5" header).  The header is about 10" above the normal water line.  Any restrictions on this?



Is there any recommended equalizer length above the water line?  Just wondering, because it will be pretty small, less than 10". 



Thx-

Rod

How Low Can a Dropheader Go!

Hi- My understanding is that with a dropper header as long as the bottom of the header pipe isn't below the top of the boiler you are okay.

- Rod

Hap_Hazzard

I'm sure there's a limit.

You're probably okay, but there isn't much to be gained. The length of the boiler risers is good--water can't splash that high--but there's no need to go back down so low unless the system risers are that low, like in a counterflow system. One thing that would have helped would be making the header a pipe size bigger than the risers, but it looks like the risers are pretty generous for such a small boiler, considering there are two of them.

TomM

my thinking

i figured 24" of boiler risers, then a drop, and then 24" of takeoffs to the zones will result in pretty darn dry steam.  But when i realized how short the equalizer is going to be, i began wondering if a short equalizer would be a problem. 



i can't think of a reason why it would be a problem in theory.......but.......

TomM

it is small

the EDR required is 239, and the boiler is 283 EDR.  I only have 6 radiators in a 2300 sq foot house.  A tall and skinny house, it should heat decent with what's left.  The manufacturer only called for one riser, of course two is better.  I used a 2 1/2" header b/c pipe is darn expensive.  

Hap_Hazzard

I can't think of one either,

unless the condensate backs up into the equalizer, but I don't know why it would unless your boiler gets flooded. Drop headers were originally a way to deal with limited headroom, so there are probably a lot of boilers out there with drop headers as low as yours but without the 24" boiler risers. If they work okay, you should be fine.



I'm not sure that there is a real advantage to making the system risers longer. The advantage to having long boiler risers is that it prevents carryover from reaching the header. Carryover is the droplets that form when the steam bubbles erupt from the surface of the water. In theory, they lose momentum before they can reach a height of 24" above the surface and fall back into the water. Any droplets that remain are entrained in the steam flow. The purpose of the header is to slow down the steam flow enough to allow these smaller droplets to coalesce and become heavier, so when the steam makes an abrupt 90° turn upwards into the system risers, the droplets, by virtue of their higher inertial mass, continue on a straighter trajectory and are flung off into the equalizer.



Pretty tricky, huh? :-)



But adding that second riser probably makes the velocity so low that much less water will become entrained in the first place, and while the velocity might increase in the middle section of the header, it's still lower than it would have been if you only had one boiler riser, and there might not be much water left to be wrung out.



So that's why I don't see an advantage to the long system risers. Any droplets that might still be entrained would be too small to settle out regardless of whether the steam is moving vertically or horizontally, and there would be so few of them that they're not likely to coalesce; collisions are less likely at lower densities. But it certainly can't hurt anything, and any water that does settle out will end up in the equalizer instead of the mains.



If nothing else, at least if we're wrong about the equalizer being long enough, you'll have plenty of pipe to make it longer.

Hap_Hazzard

By the way...

I'm just a stone's throw away, over in beautiful King of Prussia. Give me a shout if you need to borrow a wrench or do some heavy lifting.

Rod

Low Header Pipe

Hi- One of the big advantages of dropheader vs a standard header is that you can set the header pipe low and the extra length from the header to the steam mains really helps with the riser configuration especially if you are in old house with a basement that has a low overhead. The typical old house (100 year +) here in Maine has 7 feet of clearance under the floor joists. They didn't have codes back then and people were much shorter (5ft.  5" average) so I guess 7 feet was considered plenty of room.

- Rod