Oversized Boiler - best options

BigRedSteam

I have a Dunkirk psb7 that is rated for ~570 EDR and I currently have ~370 EDR connected load. 3rd floor radiators were removed before I purchased the 4200 sq ft 1909 Victorian in metro nyc. In addition, some radiators from 1st floor have been removed as well. Likely large ones by looking at riser pipe sizes. I intend to add back the radiation on the 3rd floor which will account for perhaps another 100 EDR Max. If I add back all the radiation (1st and 3rd ) floor, I will come close to 570 EDR.

Despite removal of radiators on 1st floor..house is plenty warm

My questions are:
1 - Am I better off adding back all the radiation and using the steam produced by the PSB7
OR
2 - Adding back radiation to the areas where I need heat only (3rd floor) and downfiring the boiler to come down to an estimated 470 EDR

My thinking is that if the boiler is making the steam, I cannot get more efficiency by choosing not to utilize it(TRV's, valving off rad's).

By not using the available steam I am getting a very some bouncing water line (5-6 inches) and radiator panting which I am guessing is the result of too much steam going into existing (too small) load.

Validation (or not) of the above would be a tremendous help
thank you!!

BobC

That kind of bounce indicates dirty water and suspect piping. Has the boiler been skimmed recently?

Post some pictures of the boiler and the piping above it so we can see if it's done correctly.

Boilers can be downfired some but it has to be done by someone who can check the combustion afterwards.

Bob

BigRedSteam

sincere thanks bobc and hattarasguy...

but can I realistically downfire 60% w/o causing combustion problems?

As for "not using it" - I was referring to valving off radiators and keeping firing rate the same. My assumption is that the this will have no impact on the fuel usage since the boiler is making steam at a constant rate, whether or not it gets to a radiator Conversely, If I am making the steam, I might as well turn it to condensate in a radiaotor as opposed to a pipe in the basement...correct?

BobC I will post some pics of the piping. I just had it redone after buying the house...previous owner did the replacement in 2013 and used only 1 (copper) riser to into original header(and installed boiler backwards:). My steam guy is using two risers into a 4 foot long 5 inch diam header. Installer did a great job, Boiler makes super dry steam now but I think in some ways the fact that I am getting a good volume of steam leaving the boiler has compounded the oversizing problem

Also we suspect that the returns are dirty and having those cleaned next week, which hopefully will cure bouncing water level....but again I suspect part of the water level problem is the overfiring as condensate stacks up in wet returns...I will post progress here

Fred

The most likely cause of the water bounce is oil on the surface of the boiler water (especially since you noted that you had piping work done recently) Oils from new piping work their way back to the boiler and sit on the surface of the water making it difficult for steam bubbles to break through the surface of the water, causing that heavy bouncing. Does the boiler have a skim port? If so, ask the guys who will clean your returns to show you how to do a nice slow skim of the boiler.

ChrisJ

I doubt you could downfire 60%, I think Hatteras mean't down to 60% meaning a 40% drop. Doing so will drop your efficiency some though so it's a balance between that drop, and the waste your creating by excess pressure.

We need to see pictures of the boiler and the piping around it.
Dirty water and or improper piping cause bounce, not excess pressure. In fact, I'm pretty sure higher pressure will actually help stabilize the water line rather than make it bounce.

Pictures, the more the better.

BigRedSteam

near boiler piping pics attached. Poor insulation job is mine..not installers:)

JohnNY

@Hatterasguy
@BobC

So, you guys condone downfiring an atmospheric boiler? And by as much as 40%? I have to admit, I've done this (by more like 10%-20%) a couple of ways but chose to keep quiet about it.

Years ago, a Burnham tech support agent advised me to change orifices and gave me the drill size, but they don't talk like that anymore. A rep once told me to lower my manifold pressure, but while I've done them both in the field, both those options seemed too permanent to me. I like staging method much better.

Do you have thoughts on a most practical method?

BobC

On an atmospheric boiler all you have to do is set up the two stage gas valve with a vaporstat (or magnehilic) to set the switch point and run the combustion numbers. It's not quite so easy with a wet based boiler unless you pop for a dual stage gas gun which ain't cheap.

If it's done carefully I think it's a good move. I agree that a company will not approve it because they are afraid of litigation.

Bob

Bob

ChrisJ

BobC said:

On an atmospheric boiler all you have to do is set up the two stage gas valve with a vaporstat (or magnehilic) to set the switch point and run the combustion numbers. It's not quite so easy with a wet based boiler unless you pop for a dual stage gas gun which ain't cheap.

If it's done carefully I think it's a good move. I agree that a company will not approve it because they are afraid of litigation.

Bob

Bob

You mean Dwyerstat using their differential switches.
A magnehelic is just a pressure gauge.

SWEI

After taking Jim Davis' CO class earlier this month, I'm re-evaluating the entire concept of two stage firing for non-condensing appliances. Still wrapping my head around what we learned there, but it appears there is a rather narrow range of firing rates at which you should really run them.

BobC

You mean Dwyerstat using their differential switches.
A magnehelic is just a pressure gauge.

Yes I do.

Bob

Abracadabra

equalizer on that header should have been taken off the end, not off the bottom directly underneath the main takeoff. 570sq.ft steam boiler with a 6" header might compensate.

Jason_13

I was told years ago that the code only allowed a 20% reduction and even after that you had to be within 98% of the rate be it the old rate or the new de-rate.

ChrisJ

I wish I could take a class by Jim Davis or Tim.

JohnNY

Jim Davis's class is scary. I took it about 20 years ago and have been annoying people about carbon monoxide ever since. I like to think I've personally removed some people/families from danger because of the testing and detection methods I learned with JD.
What we learned there also has a lot to do with why I'm reluctant to derate a boiler.
The bottom line is you've got to test after you make any adjustments or alterations.

ChrisJ

JohnNY said:

Jim Davis's class is scary. I took it about 20 years ago and have been annoying people about carbon monoxide ever since. I like to think I've personally removed some people/families from danger because of the testing and detection methods I learned with JD.
What we learned there also has a lot to do with why I'm reluctant to derate a boiler.
The bottom line is you've got to test after you make any adjustments or alterations.

Of course you do.
You should also test all new installations to make sure they're performing properly modified or not.

I've been lucky enough to talk to Jim a few times.

Paul48

Why not put a psb5 burner in it? Fill the void with refractory block?

BigRedSteam

Quick update

Major suspected symptom of overfiring was the the water levels and surging experienced.

I performed bottom blow 4 times until water in the sight glass was clear after repeated cycles runs. Huge improvement in performance and far quicker warm up. Clean water makes a huge difference, basics first.

Still bouncing a bit (.5-1.5 inches) so I could probably repeat procedure once or twice more. Likely gunk flowing over from the returns into boiler. A final skim is in order as well.

Added some new rads to 3rd floor which means I likely only need to downfire 20% of input to match load. Will update when that happens.