App for calculating correct existing steam radiator BTU?

LegendsCreek · September 11

Im going through my house and taking an inventory of all existing steam radiators. Charlie is coming tomorrow afternoon to look at my boiler situation, but I'm trying to get these numbers to save some time.

Looking at the Weil-McLain Boiler Replacement Guide, I was able to find the type of radiators I have (tube, I think), but their square feet of radiator per radiator section chart doesn't offer all the numbers I need to deteemine square footage so I can calculate BTU.

For example, most of the radiators have 4 tubes, with various sections. Some have 3, 5 and 6 tubes. So looking at the chart I'm not able to find my radiators. I'm hoping there's an app that will allow me to type in tubes, sections, height and width.

I wrote down every measurement in my house and am also posting a photo of one of the radiators. Thanks if you can point me in the right direction!

Jamie Hall · September 11

Perhaps the problem is in a confusion of tubes (per section) and sections? For instance, has 4 tubes per section and, I think (bit hard to count) 14 sections. The best match (doesn't have to be perfect) looks to be the lower table (tube type radiators about 2 feet high, so the table shows. 2 1/2 per section, so 14 sections would be an EDR of about 35 square feet for that radiator.

Do that for each radiator.

There's no need to calculate the BTU — use the EDR rating for the boiler. They've done all the math for you.

Grallert · September 11

Am I reading you right? Your photo example shows a four tube 16 section radiator. it's hard to see but say it's 26" tall, that's 2 1/4 sgft of steam per section. Think of the sections as slices of bread. And because you only have a limited selection of boiler sizes you really only need to get as close to one of those boiler sizes. Not too big and not too small but Charlie will have more in put. Just get as close as you can.

EdTheHeaterMan · September 11

Your list is labeled incorrectly. Where you have the word Tubes at the top, That should read Sections. For example the radiator in the picture is a 4 tube that should have a depth (width on the chart) of about 7" (you measured 6") which has about 16 to 18 sections (hard to count the sections farthest from the camera because they are out of focus). So that radiator might be the one you have listed as 18, 30, 6, 26. That is on the chart as having 2-3/4 Sq Ft EDR. So if it has 18 sections that has a total of 49.5 SqFt of radiation

The one on the top of your list (10, 17, 5, 19) would be about 27.5 SqFt of radiation.

Make a new list. Sections, Tubes, Width (what you are calling depth), and Hight where you count the sections. The Tubes, Width, and Hight where you find the closest match on the chart and place that info on the list.

Where you show a 5, 14, 4, 26 on the bottom of your list, that may be a thin tube that has 1-2/3 Sq Ft radiation. Check to see if the tube diameters are smaller that the rest of the radiators.

EDIT: After looking at your numbers, that top example in the photo I doctored up, may also may be a thin tube radiator. If that is the case then your EDR would be only 2-1/3 SqFt of radiation which would make the total 23.3 SqFt EDR

LegendsCreek · September 11

@EdTheHeaterMan and everyone else, thanks for the info. I had all the terms correct in my head but didn't write them down correctly. I've rewritten my list, and am attaching it below.

There a few problems.. 95% of my radiators are 6 1/4 width, and 4 tube. The manual I'm looking doesn't list this as an option with column, tube or this tube radiators, so I went with standard tube 7". There were 4 radiators that were a perfect fit for the thin tube, so I calculated them using that chart. (They look identical to all the other radiators, so it's possible the rest of my radiators are also thin tube, but I had to use the standard for calculation).

I didn't write down the EDR, but as you can see in the photos, my BTU calculation comes in at 165,494. If this is accurate, then why on Earth would my home have a 400k BTU boiler?

EdTheHeaterMan · September 11

Steam boiler are rated in Sq.Ft.

You match the Sq. Ft. of the total of the radiators to the Sq. Ft. of the boiler.

Now I need to do some math to double check your numbers.

mattmia2 · September 11

If you add a 30% pickup factor and figure 80% efficiency you get about 275,000 btu/hr so probably a size or 2 smaller would be the boiler you'd pick based on the EDR rating of the boiler which has the pickup factor and efficiency baked in. (assuming the 400k btu/hr is the input). The install looks like it was done by someone that knew a little about steam but not a lot so they probably either sized on the old boiler(that boiler looks old enough that the previous boiler likely was the coal boiler) or were afraid to pick something too small. You almost certainly will be fine and have a system that runs better with a 10% or less pickup factor but inexperienced pros get nervous about that. What I might do since it is oil it pick the boiler that the EDR on the ratings plate says is the right one and downfire the burner to the actual EDR plus the efficiency plus a small pickup factor, that way you can always increase the firing rate of the burner if you end up short, but I doubt you'll end up short.

EdTheHeaterMan · September 11

By using the numbers from a 5 tube radiator from the chart to calculate an actual 4 tube radiator will get you the incorrect EDR per section. That is because four 1" diameter tubes have less surface area than five 3/4" tubes. Just because the outside overall dimension of a 5 tube on the chart matches the overall dimension of a 4 tube radiator you have on site, does not make the EDR number you selected correct.

You need to get as close as you can with your actual dimensions to the chart dimensions.

If you can not get close, then you need to let Charlie do it, because he has a book called Every Darn Radiator that has more options that the WM rule of thumb guide you are using.

This is what I came up with:

but I could be wrong. I would check the middle radiator dimensions where the 8" wide radiator has 4 tubes and the 6" radiator also has 4 tubes. They are two different manufacturers of radiator and may not be on your WM Boiler Sizing Guide.

Using the same chart and numbers, my calculation is ~9000 BTUh more than yours.

You can clearly see the SqFt NET rating in the boiler specifications. That is the number that we use to select the proper size boiler. In this WM model EG boiler, the 7 section (less expensive than the 8 Section) has a NET AHRI of 185,000 BTU with a gross input rating of 299,000 BTU

If a different manufacturer has a 275,000 BTU input, that one will be closer

And with all the input, output, gross, and net BTU number to confuse you, I would stick with the SqFt rating of the boiler. EASY PEZY!

LegendsCreek · September 11

Thanks again @EdTheHeaterMan ! I double checked the questionable radiator, and it is indeed 8" wide with 5 tubes, not 4. I also realized I messed up on the current boiler BTU and remember why I got messed up.

My oil company told me repeatedly that I'd need a 400k BTU replacement (I've been discussing replacing it with them since I bought the house). They never even measured my radiators. That 400k number has stuck in my head. I went down tonight and took a photo of the tag, and it's lower than 400k. I'm attaching a photo.

Regarding all the 6" radiators, all I had to go off of was the chart I printed out, and none of them with 4 tubes offered 6" as an options, so I upped it to the 7". I'll see what Charlie thinks about it tomorrow (he's heading my way at some point). I am very curious to see what he thinks. I've got a feeling that whomever installed the system may not have been too knowledgeable about steam!

Oh, and I think I mentioned in my other thread that when I moved in there was a massive asbestos covered coal boiler that was previously tied into this one. I had an asbestos company come up and remediate it all, and they also took the coal boiler for scrap.

Jamie Hall · September 11

The number you are looking for is the line "Net 1004 sq. ft. steam" That's the number to compare to the total EDR of your radiators.

In your case, it looks as though down fired the boiler, which is acceptable within certain ranges, from 2.75 gph to 2.25 gph. That would mean the actual rating would be about 820 square feet. All losses and actual efficiency are included in that number.

Steamhead · September 12

https://forum.heatinghelp.com/discussion/comment/1810188#Comment_1810188

Another thing to check is the radiator section spacing. The standard large-tube (just "tube type" on that chart) is 2-1/2". This is the distance from the center of one section to the center of the next one.

If the spacing is 1-1/2" or 1-3/4", that is a "thin tube" type.

If the spacing is 2", it's probably one of the original American Corto rads. The chart for these can be found here:

https://www.heatinghelp.com/assets/documents/American-Radiator-Co-Corto-1922.pdf

Post a pic of anything you're not sure of.

AdmiralYoda · September 12

Just to drive the point home, with steam we don't need to worry about btu's. Calculate the EDR of all the radiators and you pick a boiler that matches the EDR load. The 30% pick up factor is built in. With good pipe insulation we can live with a little less pick up factor so if had to choose, I'd pick a boiler that is slightly smaller vs slightly bigger.

For example if you calculated your total radiator EDR to be 700 and you had to choose between a boiler that had 675 sq.ft or 750 sq.ft of capacity, I'd pick the 675 one.

The only time to worry about btu is if you are doing new construction or something. I am adding a room off the side of my house so I need to calculate its heat loss in btu's/hr and came up with 7,000. To convert the btu to EDR you divide by 240. So the radiator in my new room needs to have an EDR of 29ish. My boiler is oversized already to it works out good.

For existing construction just add up the EDR of your radiators and that is the capacity of steam (sq. ft) you need.

ethicalpaul · September 12

Please listen to everybody above and stop thinking and working in BTU. It's just too easy to get confused when talking to your contractor. Make them and yourself work in "Net Sq Ft of Steam" and save yourself so many headaches.

Charlie from wmass · September 13

He has 792 square feet of edr

SlamDunk · September 13

Fuel savings!

App for calculating correct existing steam radiator BTU?

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