EDR to determine new steam boiler size. Am I doing it right?

Ollie_Hopnoodle

Hi all, I'm replacing my steam boiler and I'm trying to find the right size. I was able to find this Aero radiator sizing chart below that determines the square feet of heating surface. These are the same radiators as the chart, just 5 tube instead of 7 tube. Since the size of the radiator in the chart is 12 inches wide and my radiators are eight inches wide (2/3 the size), I multiplied the square feet of the heating surface by .667 to get the correct number. Also below is a diagram of my floor plan with cubic feet of each room. According to my math I need a boiler that is 63, 840 BTUs. Does this seem to be close to correct? Thanks!



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EdTheHeaterMan

Can you take a picture of your radiators? We have had non professional's that have not had experience with many different radiator types pick the wrong chart for their particular radiator and end up with the wrong size boiler.

You need not calculate the BTU capacity of the boiler. You just use the SQ FT number provided by the boiler manufacturer. If your 200 number is correct then the 63-03L is the boiler for you from Peerless.
If you went with Crown By Velocity Boiler Works you would use the BSI 103

KC_Jones

Agree with the above, post a picture of a typical radiator and we can verify against other sizing charts that may have your particular radiator and double check the numbers you got.

If I was a betting man I'd say you are most likely in the ballpark, and will probably need just about the smallest steam boiler made.

Ollie_Hopnoodle

@EdTheHeaterMan @KC_Jones Thanks for responding. Here is a picture of my radiator and a picture of the radiator that the aero chart is referring to. It's almost identical - minus the width size.

Ollie_Hopnoodle

Also, I referred to the 16 and 1/2" height column for my sq ft number because I didn't take into account the 3" feet. Does that make sense?

KC_Jones

Go here and scroll to page 10
https://www.weil-mclain.com/sites/default/files/field-file/Weil-McLain_BoilerReplacementGuide_WM2012-web_0.pdf

The feet count, it's total height of radiator measured from floor. In your case I'd go with 20" which would be 2 2/3 sq ft per section. I think that pushes your number a bit higher, but not by much.

I'd still say the smallest boiler made in whatever brand you choose.

Ollie_Hopnoodle

Thanks @KC_Jones when i recalculated for 20" at 2.667 per section it ended up at 213 for all the radiators. 213 x 240 x 1.33 = 67,989 btus. I currently have oil so it seems that the Megasteam 288 at 69000 btus will suffice. But if i switch to gas I should get a boiler that is above 68,000 btus, right?

EdTheHeaterMan

Get a boiler that has the SQ FT rating. The BTU is not what your are looking for. That is because there are 4 different BTUh ratings.

The Gross Input BTUh is for sizing the gas pipe size because that is the number of cubic foot of gas the unit will burn and the amount of gas you will be paying for. If you get that 68,000 input boiler and it is 80% efficient the output rating will be lower.

DOE Output is a BTUh number the US Dept of Energy has assigned to compare all heating equipment for efficiency comparison

AHRI NET rating BTUh is the number that boiler folks use to line up with the Heat Loss of the building. Formerly the Institute for Boiler Research (I=B=R on older boilers) includes a 15% reduction in usable capacity from the DOE output for the loss of energy in the piping from the boiler to the radiators in hot water heating systems. That number changes for steam boilers to 33%.

That is why it is just easier to match your EDR sq ft. to the boiler NET sq ft rating. That number is in the boiler literature if it is made for steam. Looking at the Weil McLain boiler the EG 35 (not the EG 30) looks like the best match for your SQ FT. number you are looking for. That is their 100,000 BTU input boiler, that has a DOE output of 82000 BTUh for steam and a 62,000 BTUh AHRI NET for steam. So what BTU boiler would you have picked?
And that is not the smallest boiler they offer. although the smallest one has the same number of cast iron sections. Just a few less burners.

Ollie_Hopnoodle

Thanks @EdTheHeaterMan that’s helpful to know. That means that my current boiler I want to replace has a square feet rating that is almost double the size of my EDR at 396 sq ft, according to this IBR sticker on it. Two years ago I replaced a snow man boiler on my first floor, which is an apartment unit identical to mine on the second floor. It was replaced with a new Burnham Independence IN5I. Which has an AHRI sq ft steam rating of 358. I just pulled up the rating and specs below. If I had known what I know now I would have gotten the smaller IN4I. Is this going to be a problem down the line since it is oversized?

EdTheHeaterMan

Most steam boilers in America are oversized. That means they will short cycle because they make steam faster than the radiators can absorb it. So the pressure gets higher and the Limit pressure switch shuts the burners down. the on and off and on and off is wasteful because the burners can never get to the most efficient operating range called Steady State efficiency. Good thing the tenant is paying that gas bill LOL.

By installing the smaller boiler, the burners will operate longer and may never actually shut off by the limit pressure control. The boiler will make just enough steam to fill the radiators and keep them steaming until the thermostat is satisfied. That would be ideal if you could get that to happen.

On the Oil boiler rated at 396 sq ft, you could lower the firing rate by no more than 15% to say .85 GPH and lower the actual boiler capacity. But you need an oil burner technician to check the fire at that new lower rate to make sure if is not too low. It may already be done. They must set up the flame with combustion testing instruments. Not a DIY item.

Ollie_Hopnoodle

@EdTheHeaterMan makes sense. I recently tested the run time of my boiler when calling for heat and it shut off after ten minutes for 1:30 minutes then Shut off again at around 21 minutes for a couple of minutes. Finally shut off again at around 31 minutes for around 1:30 before finishing the heating cycle around 41 minutes. So about every 10 minutes it would shut off. Does that seem like short cycling?

ethicalpaul

It's shorter cycling than no cycling, but there are WAY worse cases out there. You can minimize it by avoiding setbacks and by ensuring you have adequate main venting.

At those timings I don't think you are experiencing very much waste.

TonKa

ethicalpaul said:

At those timings I don't think you are experiencing very much waste.

Doesn't this make an assumption his limit pressure is set low and not to some silly high value to hide the short cycling?

ethicalpaul

Yes it does, you are right. So @Ollie_Hopnoodle what is your cut-out pressure?

Ollie_Hopnoodle

@ethicalpaul It seems to be at the lowest setting.

Ollie_Hopnoodle

last week I replaced my main vent with a Gorton#1 and I did see improvement. Not sure if it's enough venting though. hard to gauge when the boiler isn't working optimally.

ethicalpaul

Pretty mercury! Don't throw that away!

Ollie_Hopnoodle

ethicalpaul said:

Pretty mercury! Don't throw that away!

Could I install this Pressuretrol on a new boiler? @ethicalpaul

ethicalpaul

You sure could, and there are several people in this forum who would if they could!

EdTheHeaterMan

Ollie_Hopnoodle said:

@EdTheHeaterMan makes sense. I recently tested the run time of my boiler when calling for heat and it shut off after ten minutes for 1:30 minutes then Shut off again at around 21 minutes for a couple of minutes. Finally shut off again at around 31 minutes for around 1:30 before finishing the heating cycle around 41 minutes. So about every 10 minutes it would shut off. Does that seem like short cycling?

So to be clear, the burner started on a call for heat when the boiler was cool (not over 150° from the previous cycle) and the burner fired for 10 minutes
At the end of 10 minutes, the burner stopped by way of the pressure control for about 1-1/2 minutes.
at the end of 1-1/2 minutes the burner started again because the pressure control dropped to the cut in pressure and continued to burn for another 8 to 9 minutes
At the end of 8 to 9 minutes the burner shut off by the pressure control for about 2 minutes
at the end of 2 minutes The burner started again and continued to burn for another 8 to 9 minutes. Things continues like this until it stopped at the end of a call for heat that took a total of 41 minutes.

If that is what happened then those cycles are far from short. 8 to 9 minutes of run time is acceptable. There are some boilers that, after the initial 8 to 10 minute initial run, short cycle 3 minutes ON and 2 minutes OFF making up to 8 or 9 ON/OFF cycles in a 41 minute call for heat. Sure it would be nice if you could lower the fire rate to make just enough steam to get to the last radiator and never go off by the pressure control. That is what we strive to do. Getting the correct EDR number and the correct Sq Ft of steam boiler output will get you close and sometimes you will get it to work. I have done that on about 1/2 of my steam jobs installations. The other half were learning experiences and others were that they just don't make a small enough oil fired boiler. But I never has a short cycler.

I did work on several short cyclers though. Seems that those cycles add up fast and parts break more often on them. That is why we size for EDR and try to get it as small as will fit the job. Bigger is not Better!

@ethicalpaul, I was wondering.. with all the testing, and monitoring, and those cool videos you posted... Does you boiler cycle on the pressure control? If YES, how long is the run cycle between pressure control off cycles?

If NO... Wow congratz!

Ollie_Hopnoodle

@EdTheHeaterMan I ran this test when I was trying to time steam running from my header to my main vent. I didn't know about what the Pressuretrol actually did at that point. But, I will test it again and focus on the shut off timing during my next heat cycle, from a cold start. I'll report back.

ethicalpaul

@ethicalpaul, I was wondering.. with all the testing, and monitoring, and those cool videos you posted... Does you boiler cycle on the pressure control? If YES, how long is the run cycle between pressure control off cycles?

If NO... Wow congratz!

Thanks for the compliment! I'm just a little bit oversized because Peerless only goes down to about 230 sq ft with their 63-03L and I'm at about 180-200 EDR in my small house, so on a looong call for heat it would eventually hit the pressuretrol cut-out. It would have to be about a 6 degree recovery or more.

BUT...

I don't like building pressure just for the sake of building pressure while burning expensive gas, so I have an additional pressure switch (Dwyer) wired up that triggers at something like 10 inches of water column (roughly 1/3 PSI).

When that switch closes, it triggers one of those nice little DIN rail timer modules and that interrupts my thermostat's call for heat for 10 minutes. This gives the radiators time to radiate away some of their heat into the living space without the burners firing. That one will trigger a few times on a setback of like 3 degrees. It basically makes the return from a setback take longer.

It's a very simplified version of some of what I understand the Ecosteam would provide.

During a normal call for heat, I never cut-out on pressure on either switch.

JUGHNE

It may just be the angle of the camera, but your pressure control does not look level.

Mercury switches must be mounted with a level reference point.

Look in the rear right of the control and you will see the swinging pendulum meant to point to the mark below it, inside, on the case.

If not level/plumb the accuracy of on/off points will be wrong.

EdTheHeaterMan

JUGHNE said:

It may just be the angle of the camera, but your pressure control does not look level.

Mercury switches must be mounted with a level reference point.

Look in the rear right of the control and you will see the swinging pendulum meant to point to the mark below it, inside, on the case.

If not level/plumb the accuracy of on/off points will be wrong.

I think it is the camera angle/. look at the boiler jacket behind it... maybe a little off but not like this house:
Was this built by a builder in Pizza Italy or, is the street on an incline?

Steamhead

It's "Pisa". And, from the looks of the trees, the street is on an incline.

ethicalpaul

That's what I found odd...the big tree is acting like the street isn't inclined.