May have identified the issue - OVERSIZED BOILER - thoughts?

caseycamire · December 2019

Hello all - I've been bugging you guys the last few weeks for ideas about why the heck my radiator air vents don't close and howl like banshees during calls for heat.

Questions:
Am I actually oversized when calculating for the hot water baseboards? Would an oversized boiler explain why my air vents howl during calls for heat? Information below.

Long story short, I finally calculated my total heat demands for my heating system. It is a three zone, steam/hot water/radiant floor system, with steam heating the kitchen on the first floor and all of the second floor, base ray hot water cast iron baseboards in the remainder of the first floor, and PEX radiant floor heating on a recently constructed porch/mudroom.

Steam: 6 radiators, 154ish EDR, about 36,753 BTU/hour. (EDR x 240 BTU/sqft)
Base Ray: 35.5 total linear feet, up to 630 BTU/foot, total 22,365 BTU/hour (liner ft x 630 BTU/ft)
Radiant Floor Heat: 133ish square feet, assuming 25BTU/sq foot, about 3,325 BTU/hour (sq ft x 25BTU/sq ft)
Total: 62,443 BTU/hour (steam + base ray + radiant floor)

Boiler: Weil McLain P-SGO-5 Series No. 2 steam boiler with hydronic coil feeding baseboards and radiant floor
D.O.E. HTG Capacity - 175,000 BTU
Sq. Ft. Steam - 546
Total Steam BTU - 131,000
link to boiler pic: https://photos.app.goo.gl/Y2Euuufxxs1RTA8B6

Now, I'm not a pro, but my top end BTU/hr estimate accounts for a 1.2 correction factor on the steam EDR calculation (manipulated it until the numbers started matching EDR tables for radiators similar to mine), and with 210F water to the baseboards!! I could multiply my calculated BTU/hour by over 2 and still not be using my full boiler BTU capacity!

Note: all air vents are new (replaced in the last year) Gortons, and main vents are 2 gorton number 2s on the ends of the main going to each end of the house. The steam lines have not yet been insulated.

Thanks as always!

Jamie Hall · December 2019

Well... yes, your boiler is oversized. By a good bit. Which makes control.. difficult, even if it were all steam. Adding in the demand for the radiant and the baseray makes it more interesting -- but not impossible.

First, though, on the howling radiator vents. That's often, though not always, a symptom of two problems: first, not enough main venting and second, too high a boiler pressure. The latter is easy (usually) to fix. On the boiler there will be -- most likely -- a pressuretrol. If it makes sense to you, figure out how to set it as low as possible. If it doesn't, post a picture of it and we can help you out on that (maybe it's in that link, but I can only get at the first picture).

On the second, many of us would suggest that for such an oversize boiler you place a delay timer on the boiler, to cause it to stay off for a while -- perhaps 10 minutes, but opinions and needs vary -- after it shuts off on pressure. In this case, this delay timer would go only In series with the pressuretrol -- because the baseray circuit and the radiant floor will both need (and probably have) aquastats on them which will ask the boiler to run up to a certain temperature, but not to make steam.

I presume the radiant floor has a mixing or tempering valve in its circuit which brings the water temperature down to where it needs to be.

Is there a separate circulator for the baseray and one for the radiant?

I have a definite vision for how I would control this mix -- but would you post how, in fact, it really is controlled? What thermostats you have and what they are wired to, and what pumps or valves?

caseycamire · December 2019

Hi Jamie! Thanks for the response!

My pressuretroller cut in is currently set to 0.5psi (and the plastic wheel under the cover is set to 1).

I recently removed and cleared the pigtail, but I'm considering replacing the pressure gauge and pressuretroller, since the boiler never seems to shut off due to pressure, and the gas that's venting during the howling is definitely steam.

Usually, the cycle starts, air vents, steam comes up and valves close, then a few minutes later they start re-opening and venting steam. Might be overpressurizing due to oversized boiler and faulty pressuretroller? The pressure gauge goes to 30PSI, but I've only ever see it touch 2PSI by end of the cycle, and I've never seen the boiler stop before the thermostat ends the call for heat. But, I don't know if the gauge/pressuretroller is any good. The pigtail was full of crud when I cleaned it a couple weeks back.

I'm thinking of tapping another hole to mount another Gorton 2 at the long end of my main. Bad idea? Good idea?

The delay timer is an interesting idea.

You are correct that the radiant floor has a mixing valve that regulates temp feeding the floor. The base-ray and the radiant system run off separate recirculation pumps.

There is one thermostat upstairs that controls steam (honeywell, programmable), one thermostat downstairs that controls base-rays (honeywell, programmable) and one thermostat that controls the radiant floor on the porch (wirsbo? non-programmable).

Radiant floor pump/valve panel: https://photos.app.goo.gl/7qdP6gfoATEG2bsZ8

Base-Ray recirculation setup:
https://photos.app.goo.gl/tVueeQ3qj31tHt719
One picture is the complete setup including expansion tank, another is close up of recirculation pump.

Hap_Hazzard · December 2019

On that Pressuretrol, try taking the cover off while the boiler is firing, and lift the right side of the rocking mechanism with your finger or the tip of a screwdriver. It should move easily and engage the microswitch. You should hear a "click" and the burners should cut out and cut back in when you release the rocker. If that's the case, the Pressuretrol is working, but it's not calibrated correctly. If you hear a click but the burners don't cut out, the switch may be defective or incorrectly wired. If you don't hear a click, or the rocker won't move easily, or if the burners don't cut back in after you release the rocker, either the switch is bad or there's some kind of mechanical issue that needs further investigation. Give it a try and let us know what you find.

acwagner · December 2019

Since this is a mixed steam/hot water setup, you might want to get this posted on the Main Wall instead of Strictly Steam so the hot water folks see it. I think @Erin Holohan Haskell can do that if you ask.

JStar · December 2019

We generally don't include any hydronic loads in our steam boiler sizing, which puts your boiler way over size. You can downfire your boiler to a certain point. That may help, but it might not be enough.

KC_Jones · December 2019

The smallest SGO made is rated for 354 sq ft of radiation (SGO-3) By your numbers that one would be ~26% over sized. The one you have would be ~95% over sized.

The pickup factor in the boiler ratings takes care of the water side. Also your baseray numbers look low, I see a rating of 860 per foot on steam. Remember steam has latent heat that boosts output over similar water temps.

acwagner · December 2019

@Jstar you don't include hydronic loads even when half of the emitter load is hydronic? If I understood his description, only the second floor is steam. The baseray and radiant floor are hot water.

Erin Holohan Haskell · December 2019

acwagner said:
Since this is a mixed steam/hot water setup, you might want to get this posted on the Main Wall instead of Strictly Steam so the hot water folks see it. I think @Erin Holohan Haskell can do that if you ask.

I've moved this to The Main Wall. Thanks!

Jamie Hall · December 2019

This is an odd situation regarding sizing, since the hot water load is probably pretty close to equal to the steam load. I'd have to do some real analysis of the two loads. I suspect that the normal pickup factor would cover it, but...

KC_Jones · December 2019

Oops!

Misread the baseray as being steam, so just makes the over sizing even worse than my numbers. That’s crazy over sized, but not the worst I’ve seen posted here.

KC_Jones · December 2019

I’d slot this into the category of being oil and actually can’t get small enough. What he has is just silly if I’m being blunt.

JStar · December 2019

> @acwagner said:
> @Jstar you don't include hydronic loads even when half of the emitter load is hydronic? If I understood his description, only the second floor is steam. The baseray and radiant floor are hot water.

Right. The idea is that once the boiler is making steam, it has to match the condensing load of the emitters. Since the boiler water is already hot (and returning from the HW zones hot), you aren't shedding any additional significant BTUH load. You size to the steam side, and the piping pickup factor covers the rest. If the HW zone is bigger than the PU factor, you should consider alternative options.

acwagner · December 2019

@caseycamire back to your controls. Is the steam zone thermostat the only device that actually makes the boiler fire, or is there also an aquastat or something on the hydronic side that will make the boiler fire?

May have identified the issue - OVERSIZED BOILER - thoughts?

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