Sizing a new steam boiler with inlet orifices extisting

Charlie82

Looking for guidance on sizing a new 2 pipe system steam boiler. About 17 of 23 convectors and radiators have extisting orifice plates installed probably original 1931. Should I still install a new boiler to the radiation edr or measure the orifice hole diameters and use that value in the edr calc. I'm concerned that if I install a boiler to the calculated edr which is 859 that it will short cycle on pressure. The existing boiler which was 568 edr never evenly heated my house so I know I need to up size.

nicholas bonham-carter

What is the EDR of the radiation, in relation to the heatloss of the building? I know the steam whisperer has sized some boilers to the heatloss of the building. Maybe Dave will chime in here with some tips for you.
The unevenness of your heating with the old boiler may be due to a problem with traps/venting, more than a missizing of the old boiler, or the fact that not all radiators may have orifices.
Sizing to the aggregate orifice capacity seems pretty good to me.
A two stage gas valve would be helpful here, or a burner with some variable adjustability.—NBC

KC_Jones

What is on the emitters that don't have orifice plates? Without something to properly regulated those, it may be causing your imbalance.

IMHO unless it's a really extreme case, an undersized boiler isn't going to be the cause of uneven heat.

If memory serves from Dan's book, orifice plates would typically be sized to fill 70% of the radiation. In your case 859 would be about 600. I am making many assumptions here, but doing it to illustrate how that current boiler might actually be closer than you think.

JUGHNE

Is the existing boiler leaking? Why must it be replaced?
If it is working, I would put orifices on all emitters.

Is all the piping insulated with at least 1"?
Do you do any setback overnight?
What pressure does it run at for an extended time when you are near outdoor design temp?

From my experience with orifices, it seemed like the orifice would restrict air venting of the main thru the emitter.
I would recommend venting the ends of the steam mains separately rather than rely upon all air having to be pushed thru the orifice/emitter/trap and into the dry return to the air venting.
This seemed to get the steam to the farthest emitter quicker for better balance.

PMJ

An orifice plate simply reduces the max possible flow rate of steam into a rad. That way they prevent the rad they are on from taking too much of the available steam capacity with the boiler running which forces steam to go elsewhere - an evening out effect. To me the more effective orifices are the ones in the ingenious output traps like the Mouat ones which then limit the flow only AFTER the rad has some fill and is actually producing condensate. In my system that effect on first fill is pretty dramatic and quite effective at getting things started up fairly evenly.

Everyone knows I don't fear the "too big" boiler as short cycling is easily controlled other ways. I think I'm going to redefine a "short cycle" as simply a cycle which occurs when you know another firing isn't needed but your standard pressure control doesn't. But all that aside, I would make absolutely sure I really needed more boiler before paying for one. Big boilers can make uneven heat too - mine sure was when I moved in.

What are the reasons you think it is too small beyond evenness of the heat? In bitter cold does it run flat out and still not fill the system enough to satisfy the tsat?

Charlie82

My calculated heat loss comes out to 139,000 btus. House is 2500sqft, original single pain windows, with brick and block wall s no in wall insulation outside of Allentown PA

The extisting boiler just started leaking at the end of the season this year it was neglected for years before I bought the place I install new ft traps at the end of the mains and install new air vents also, so there was a huge improvement right away, all the mains are insulated with 1-1/2" covering.

The radiator s with out orifices obviously heat much quicker then the the ones with orifices. If I close off the few that don't have orifice plates I still don't get much of a difference of heat at other units.

The only way I truly get that steam heat intensity is if I close off one of the two 3" steam mains which heats each side of my house then I get real heat. So by doing this is what's telling me the boiler is under sized.

I just keep thinking a boiler rated at 859 edr seem huge reading other threads on the wall and compared to the heat loss calc but I know the boiler that's in just isn't doing it.

Thanks in advance.

Charlie82

As far as pressure the best I every saw with haveing half the house isolated was about 10 inches of water column so 5or6 oz. Most times it runs at 6in of water column 3.5oz

PMJ

Sounds to me like a little small too then.

So now I switch gears and argue for not too much worry over being too big. If I had to replace anyway I would put in extra. It is just too easy to spread the required run time out evenly and avoid all pressure and unwanted cycles altogether. Plus, if you ever toyed with the idea of trying natural vacuum (which I have found is the smartest, least expensive, and most self adjusting heat control system there is), you will need extra boiler to have significant off time for the vacuum to do its stuff.

Charlie82

I did give some thought to vacuum. I wondered why it wasn't one originally for all the benefits. I'm pretty sure all the vents and traps are originals they were really ancient Looking and neglected

Canucker

> @Charlie82 said:
> My calculated heat loss comes out to 139,000 btus. House is 2500sqft, original single pain windows, with brick and block wall s no in wall insulation outside of Allentown PA
>
Are you sure about the inputs on the heat loss calculation? That comes to 55 btu/hr per sq ft. Seems on the high side if you have windows and doors that close

Charlie82

I used a hvac computer program on the heat calc should be right.

Fred

Something seems wrong with your EDR calculation. I have a 5000 Sq. ft. Home with 700 total Radiator EDR and that heats the house just fine at sub zero temps. Pretty much same construction as your house, all masonry walls, no insulation in side walls, original, singe pane windows. Maybe someone was just too aggressive with the orifice sizing???

PMJ

> @Fred said:
> Something seems wrong with your EDR calculation. I have a 5000 Sq. ft. Home with 700 total Radiator EDR and that heats the house just fine at sub zero temps. Pretty much same construction as your house, all masonry walls, no insulation in side walls, original, singe pane windows. Maybe someone was just too aggressive with the orifice sizing???

I have 1000edr for 3500sqft same construction plus triple track storms over the leaded glass originals. Never fill the 1000 in sub zero and like it that way......extra all around.

1Matthias

Our 3600 Sq. Ft house heats quite happily with exceedingly patchy insulation and 465 EDR, up to when it's below 0 and having to recover from a 3-4 degree setback. All original windows, all original drafts. ;P Rarely do the rads fill except when there is an extended run period.

Charlie82

As far as my edr numbers I basically used a governor bros element value along with the proper cabinet height I have sixteen such convectors in various width and heights and the rest are rads. My elements are 8" x 8" so I just figure that 8" would fall been the 6" and 9" listed Edr values. See attached pictures for elements

Fred

Charlie82 said:

As far as my edr numbers I basically used a governor bros element value along with the proper cabinet height I have sixteen such convectors in various width and heights and the rest are rads. My elements are 8" x 8" so I just figure that 8" would fall been the 6" and 9" listed Edr values. See attached pictures for elements

If you are comfortable thatyou calculated the EDR correctly, then I have to think those orifices are too small to allow steam to get where it needs to be and, given steam will take the path of least resistance, it is probably going to the rads that don't have ofifices. What room is the tstat in? Is it in a room with a rad that doesn't have an orifice? Does the boiler shut down when that room is satisfied and the others are not as warm? In any case, I suspect that is part of the cause for uneven heating. I would figure out what is happening before I sized the boiler. Maybe the rads without orifices need them so that they don't steal steam from the ones that do.

EBEBRATT-Ed

@Charlie82

Your making the assumption that your existing boiler is puutting out what the name plate says.

it's probably not over fired but certainly cold be under fired.

If it's oil fired you would need to check the oil pressure and the nozzle size.

If it's gas you would need to check oarfice size and the gas pressure.

AMservices

It's safer to be a little over sized then under sized with steam.
Over sized there's options to adjust firing rates, on off cycle and balance steam distribution.
Under sized the boiler runs nonstop to only heat parts of your home.
I think you on point with your estimation on EDR.
If your steam traps are working properly and your main venting is adequate, you shouldn't build pressure before the homes heated.
Dont let a 200k boiler bother you. Be more concerned about finding the right contractor to install the boiler.

PMJ

AMservices said:

It's safer to be a little over sized then under sized with steam.

Over sized there's options to adjust firing rates, on off cycle and balance steam distribution.

Under sized the boiler runs nonstop to only heat parts of your home.

I think you on point with your estimation on EDR.

If your steam traps are working properly and your main venting is adequate, you shouldn't build pressure before the homes heated.

Dont let a 200k boiler bother you. Be more concerned about finding the right contractor to install the boiler.

Exactly right @AMservices . Many options with an oversized boiler. There are no options with one too small. I see no advantage to the "perfect" match whatever that is - only fewer options.

Gsmith

Remember there are really no exactly correct boiler sizes for a given structure. If done "right" the boiler matches the structure heat loss only on the design temperature day, most other days it is oversized, some days, when below design temp it is undersized. So, within broad guidelines, don't be too concerned, go a little oversize if worried as others have said, less problems with slight oversize than undersize.

Charlie82

Great thanks everyone for the input. I appreciate those who took the time to give their advice, I'll keep you posted on my final out come.

jumper

Charlie82 said:

I did give some thought to vacuum. I wondered why it wasn't one originally for all the benefits. I'm pretty sure all the vents and traps are originals they were really ancient Looking and neglected

Cynics and paranoics suspect somebody was a good at selling vents and traps in the olden days. (Hey I resemble that remark) Otherwise Moline types would be common.

Charlie82

Just finished my install of my new Peerless Series 63 six section boiler. 3" risers into a 4" drop header. Had it running for about an hour straight stays at a steady 1/2psi and plenty of heat a all convectors major difference from the old undersized 568edr boiler. Installed four new Gorton number 2 vents.

gerry gill

Nice job- sounds like you got it running well on that orifice system too.

Charlie82

Thanks. So far so good.

PMJ

Looks great. As the season moves along post some feedback about changes in operation with the bigger size boiler.

Charlie82

Will do thanks