Steam Boiler Sizing (Convector radiators)
Hi,
I'm trying to determine the proper steam boiler size for my system based on my radiators. I have several convector type steam radiators and I can't find square footage numbers for these units. Can anyone help or direct me to a link where I can size them?
Here is what I have:
I have 4 of these units which are 32 inches wide x 6 inches x 6 inches.
The next one is the same type as above, but this one is only 22 inches wide x 6 inches x 6 inches. I have just 1 of these units.
Next is another convector, this one is 68 inches wide x 6 inches x 6 inches. I have just 1 of these.
Next is I believe an Arco Sunrad type, It is 40 inches wide, 5 inches deep and 16 inches tall.
Finally I have this small radiator. 22 inches tall, 6 inches wide and 5 inches deep, 4 sections of 4 tube. I think this one is 1.8 based on this:
Thanks for your help!
Comments
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How are you measuring 16" on this radiator?
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
1 -
You have this type of Arco Convector and it will take me some time to do the math on them
Still need the answer on how you measured the 16" in my first reply comment
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Option B. Top of the metal to the bottom.
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Here is the first calculation. Based on these measurements the EDR for this convector is 28.9
If the measurements are different please correct me.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
1 -
OK in the book that is a 20" radiator. 4" legs. 18 sections = 40.5 EDR
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
1 -
Ok,
So for the 4 units that are 32 x 6 x 6, that's 29.8 for each one x 4, which is 119.2 for those 4 radiators. For the 22 inch, I will call it roughly another 19.26 Sq foot based on 2/3 size of the 32 inch versions. For the long one (68 inches) I get 67.43 sq foot.
119.2 (4 -32 inchers)
19.26 (1-22 inch convector)
67.43 sq foot (Long convector)
40.5 sq foot ( in wall panel)
7.2 (for the tiny bathroom radiator)
Total 253.59 square foot of radiation.
253.59 x 240= 60,861.6. BTU. x 1.33 = 80,945 BTU. Does that sound right?
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This one is 60.3 of my measurements are correct.
There are adjustments based on the cabinet dimensions and the actual cast iron dimensions. This is the chart I am using and you can see if the cabinet size changes the amount of the heat output changes a little for the same size cast iron convector.
As you can see on your 68" long radiator, changing the cabinet hight by just 2" can change the EDR up to 4 Sq Ft. That is why I need you to doublecheck the measurements
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
1 -
All of the cabinets are 24" tall.
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The last one.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
0 -
So this changes my numbers a tiny bit:
119.2 (4 -32 inchers)
19.9 (1-22 inch convector, assuming it is really 23 inches based on the chart sizes)
60.3 sq foot (Long convector)
40.5 sq foot ( in wall panel)
7.2 (for the tiny bathroom radiator)
= 247.1 X 240= 59,304 X 1.33 = 78,874 BTU
The next question is, I have a Weil McLain EG40 which is 125k BTU I believe. Is it worth having someone down-fire my burners? I have my boiler set to run once per hour on the Honeywell thermostat. It has plenty of main venting and the pressuretrol is set about as low as it can go. A typical cycle is about 20 minutes and the boiler shuts off due to the thermostats reaching temp, never due to pressure which almost never rises above 0 on my 0-5psi gauge. So I'm not having any functional issues, but wondering if it could be running more efficiently if it was down-fired a bit?
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Yes that sounds correct, but do not convert to BTUh for the boiler size. There is a NET SqFt rating for each steam boiler. That is the number you should use to select the proper boiler.
For this manufacturer of boiler, you should select the .80 GPH oil fired boiler, 112,000 BTU input and perhaps use a .75 GPH firing rate for you home
If you are selecting a Gas boiler then you need the BSI 103 that has a 103,000 BTU input.
An 81,000 BTU input boiler will be too small for your home.
This is why it is NEVER a good idea to convert Sq Ft EDR of radiation to BTU when selecting a steam boiler. The Conversion factors are there for engineers to select the proper radiator for the room based on the Heat Loss of that building, and whether the radiator is going to be used as a hot water radiator or a steam radiator. Since you already have the radiators because some dead man already did the selecting for you many years ago, you just need to match the total EDR of your connected radiation to the NET SqFt of the boiler.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
0 -
Ed,
Thank you for all your help. So if I'm at 247 square feet of radiation. It looks like the Weil McLain EG35 (258 sq ft) would have been the best choice for me if I'm reading this chart correctly, but instead I have the Weil McLain EG40 which is 321 sq ft. Would you still suggest down firing the boiler a bit? Or given that I'm not really having any issues, leave it alone? Would there be noticeable improved efficiency and lower gas bills if I down fire it?
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Correct, you could have used the next size smaller, but you are not drastically oversized. And the EDR numbers may be a little off if your cover dimensions are different than the ones I posted.
The only down firing you can do on the boiler is to reduce the gas pressure no more than 12% and that is not a recommended procedure. It is just something I know will work from experience.
You have the 4 section boiler and the EG-40 already has the smaller firing rate (the 45 has the higher firing rate) and perhaps lowering firing rate more may save you a small fraction on your gas usage. The problem with adjusting the gas pressure lower is that the efficiency of the actual flame will also go down. So there is a sweet spot where the lower flame size will be less efficient but the lower input will counteract that loss of combustion efficiency. The Laboratory at Weil McLain has already done those tests and have determined that the boiler you have is best set at 125,000 BTU Gas input on the low end and 150,000 on the high end (EG-45).
Going any lower than say 112,000 BTU input may actually be less efficient and cause the gas usage to go higher. Any savings you might realize from your fiddling with the gas pressure will only be in the 2 to 3% range anyway, not worth the risk. …And you need a technician that has the time to play with it and check the adjustments with a combustion analyzer. Do you have a friend with a combustion analyzer? Otherwise you will need to pay for a pro with the proper equipment to do these adjustments for you, If your total annual gas bill is $1000.00. And you pay the technician over $150 for the service to do the adjustment, your savings will be about $20.00 a year.
So unless you are experiencing a major short cycling issue, I would leave it alone.
Edward Young Retired
After you make that expensive repair and you still have the same problem, What will you check next?
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Thank you Ed!!!
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