I first saw my current house when it was cold out... The second trip to take a look found it to be freakin' cold... The day of close I recall being bitter, and there was snow predicted... Then I had to go to Florida for a couple weeks for business, and when I got back there was snow, and it was still bitter cold... Inside the house, for all its clearly visible faults, it was always nice and warm... Through the inspection, I found my boiler was 10 years old, and considered a mid-efficiency unit... I didn't think much about the heating system then until the summer, except to know I was going to have to re-run most of the piping, which is simple basic plumbing and requires not too much mental effort on my part... The radiators are all in very good shape and are probably only 10 years old as well, so I thought I'd be good there, and for the most part I am... I decided I needed to replace the radiator in the living room because of space... The unit is very large in there, and it simply isn't going to work with my two monster recliners... So I found some nice wall mount panel style radiator, and figured I was set... Now of course by now its summer and the boiler is off, and drained since I had to cut out the old radiator to put down the cherry floor... So as I try to figure out the exact size I need, I find that not only do I need to know what the general temperature I want in the room is, but also the operating pressure of the unit, and the input and output temperatures of the boiler... This is the point at which I bang my head against the wall for not noting what the gauges said in the middle of the winter...
So the process went this way... Track down a manual for the boiler that has been discontinued... Find out the base line for that particular unit in terms of pressure, and temp ratings... Gusesstimate what the boiler output temperature setting is (no digital gear here folks, its a rough dial, and I'm sure you set it by trial and error)... Then I researched what the BTU output of various kinds of cast iron radiators was to get a good estimate of what was being put out last winter... (you would not believe how many different shapes and sizes of those bloody things there are) Then with that info, I delved in to the paperwork on the new stuff I like... Problem is they only rate it at 180 degrees, and my boiler is running around 235... Now as a side note, I recall the radiators were freakin' hot last winter, to the point you didn't want to touch them... That works well with the 235 number for sure... However, we all know water boils at 212 right?... However, under pressure, the boiling point goes up... My handy dandy Pipe Fitter's Guide tells me it boils at 239.4 at 10psi, and 249.8 at 15psi... The boiler tops out at 240 supposedly, so I should be safe in terms of not getting steam, so long as I maintain that 12psi... If it were to get down to 8psi, I end up with steam, and that's not good... But I digress...
After calling the company and confusing them as to why I'm running at 235, they did come up with the needed BTU output of their equipment for me...
Realistically, I am only replacing the one radiator, so I don't want to effect the balance of the whole house, which is why I'm working with the numbers assuming 235deg water... If I get the correct size replacement to correspond to what was there which I know will be sufficient, I know I'll be ok... Also, I will be able to roll the temp on the boiler down a bit to around 215, which makes the likelihood of getting steam almost nil... Doing that means the boiler will run a bit more frequently, however it should run a bit more efficiently since I've added insulation to the house, and I'm separating the basement from the main floor with zone valves and a separate thermostat... (basically I won't be wasting heat all the time in the basement which holds it quite well to begin with, and the boiler can do its thing more efficiently for upstairs...)
At any rate... 6 weeks from now, the new radiator comes in... Right at the end of September... Just on the cusp of potential cold... Its gonna be close...