steam boiler replacement

songdog

Greetings!  I currently have a two pipe steam system with a 50+ year old gas fired WM HG7 with 384K output.  I have calculated the EDR of my radiators as 531.5, multiplied by 240 to arrive at 128K. 

Contractor proposals are all over the place as far as size of boiler. 

When sizing a new boiler, what margin should be used?  I have seen values up to 1.5. 

Can you recommend a boiler manufacturer and size. 

Thank you!  Gordon

Jamie Hall

It always pays...

to double check your EDR figures; one rarely makes a mistake -- but it does happen.  Having said that, it would appear that your existing boiler is oversized.  This is not that surprising -- radiators may have been eliminated or other changes made to change the total EDR.



As to the "pickup" factor... the general range seems to be from about 1.3 to about 1.5 -- but it depends a lot on how well insulated the steam mains are.  If they are well insulated, you can get by with a smaller pickup factor (as well as making the whole system work better!).



Not surprised that proposals are all over the place.  It might be worth asking each contractor how he sized the boiler he is proposing... if only to enjoy some of the more humourous answers!

nicholas bonham-carter

boiler selection

choose a contractor first, who can read and follow a boiler installation manual, then follow his recommendations on the boiler, which should be distributed locally, by someone who keeps spare parts on hand [like a new section!].

make sure you include in this new setup a good low pressure gauge, and a vaporstat [on the same brass or copper pigtail] to keep the pressure in the 2-8 OZ. range. also pay attention to the air removal part of steam system operation--how does the air get out, so the steam can come in? if it is a vapor system, there may be other considerations, so a picture of your radiators would enable some identification. 

lastly, don't forget the supply pipe insulation!--nbc

more thoughts added later:

resist the temptation from some contractors to add a pump, and leave it gravity return. a pump is inherently prone to failure, and what then? if your pressure is low, then gravity will have no problem in putting condensate back in the boiler, during steaming.

a copy of "the lost art of steam heating", if you don't already have it will help you understand, and sometimes educate your contractor. it's available from the shop here.

The Steam Whisperer (Formerly Boilerpro)

Another perspective

Since you have two pipe steam you may want to delve even deeper into the sizing issue.  I would suggest you also take a look at the current heat loss of the building.  Two pipe steam systems can be easily adjusted to reduced heating loads, so that will allow an even smaller boiler which will use even less fuel. 

The best approach would be to calculate the heat loss of every space a radiator heats, check the size of the radiation against those loads, and then adjust the radiation input by using supply valve orifices.  If your supply valves are in need of replacement, there are valves available that allow the orifice to be adjusted after installation to allow easy fine tuning once the system is running. 

Next measure your piping  and calculate its heat loss.  Add up the the heat output of the resized radiation and the piping and you now have the new boiler output that is necessary.  You may want to add a little extra to speed up warm of the system in the spring and fall.

If your supply valves can still be adjusted, you may be able to skip the orifices and just the balance the system with the valves and still install a smaller boiler.  The orifices do seem to do an excellent job of making sure all the radiators heat at the same time since they restrict the flow of steam to the radiators until the mains fill completely.

I have used both these methods successfully, pulling out 350,000 input boilers and replacing them with 120,000 input boilers.