Determining Boiler Size

Danny Warshay

I am replacing my old oil steam boiler with a new gas one, and am trying to determine which size of Burnham boiler to purchase. Despite being a complete novice, I am sizing this myself because I have received such discrepant estimates from a few different contractors: from 325 NET IBR which I am sure is way too low to a 9 section boiler that I know is way too high. My current old oil boiler is a 7 section, but I have no idea how to determine how much steam it produces.

I understand that for a steam system I need to determine total square footage of steam. I have measured the sizes of the radiators throughout my house (10 tube types and 7 convector types) and using old tables that another Wall user was gracious enough to point me to, I was able to determine that the total heatload is 431 square feet of steam. That corresponded very closely to the measurements of one of the contractors and leads me to believe that I need to purchase the PIN 6 model which produces a maximum of 450 square feet of steam.

Because I am a novice, however, and because 431 would be pretty close to the max for this model, and because I'm told that you absolutely cannot be under, I am a little nervous about screwing this up.

One thing that has thrown me is that contractor whose measurements concluded a need for 445 square feet is recommending a boiler that produces 546 square feet (he was from my current oil company and was recommending an oil boiler, but I assume the square footage of steam requirement is the same for gas). When I asked him about it, he said that he was adding a bit more because of piping, but avery helpful Burnham technical person said that their ratings already account for piping.

I'm told, however, that if I have any "unusual" piping, that I need to bump up my estimates.

So now I am confused, and worried about screwing this up.

I guess my questions are several:
1) Do I need to account for anything beyond simply the measurements I have done of the radiators?
2) If I do need to account for piping, and especially unusual piping, what does "unusual" mean? I am told that I have a bullhead? piping leading out from the boiler and could try to describe the rest if that is helpful/necessary.
3) How exact do I need to get this? In other words, is there any buffer in these measurements? I know that I could just opt for one size up, but that seems like a tremendous waste to go from 450 to 540 if I don't really need to.

I really appreciate any assistance anyone can provide and would be happy to provide any additional detail or measurements that would make it easier to help.

I am amazed that such a helpful "community" as this exists, and I look forward to helping someone else once I become better educated myself.

Big Ed

Measure

You need to add for uninsulated steam mains..

Unknown

Danny

As you have already been told, the Net ratings for steam that are shown for the steam boilers already include a hidden pickup factor of 33%. By unusual pickup losses or piping we mean things such as uninsulated pipes and mains or unusually large pipes or pipes that are located in unusually cold environments such as cold crawl spaces. If none of these apply then the PIN6 would be your proper choice provided the sizing charts you used are fairly accurate. As far as the oil-fired boilers go, the steps between boiler sizes (sections) are usually a little bigger. Our V85 Steam boiler would be the choice if you were to go with oil and it has a rating of 512 square feet. Hope this helps.

Glenn Stanton

Manager of Training

Burnham Hydronics