ymha

ren

 I liked to know if a steam boiler can be modulated, in terms of psi,  as a result of  the outdoor temperature. Would controls be able to switch the boiler to low fire or high fire as the outdoor temperature changes.

                                                       Thank You



                              

nicholas bonham-carter

Modulating burner for steam

Usually, a vaporstat will control the hi-lo firing. At a call for heat, the burner will come on hi, and when a preset pressure has been reached, say 6 ounces, the burner will switch to lo-fire to maintain that pressure. If the outside temperature drops, the radiators will have to condense more steam to keep up, and the pressure will start to drop below that set point, triggering the hi fire for only as long as needed to catch up.

Steam heating systems, when properly maintained, with good venting, run best on less fuel at pressure below 10 ounces.--NBC

Jamie Hall

PSI

is not the controlling factor for steam heat.  As NBC notes, steam heat runs at less than 2 pounds -- usually less than half a pound -- per square inch; the pressure has almost nothing to do with the temperature of the steam.  The controlling factor is run time.



Modulation of the burner input may be useful in some situations, particularly installations with variable loads such as TRVs controlling some or all of the radiation or, very rarely, when there is a large pickup factor for some reason.



Some larger installations, again usually where there are large variable loads, may control run time by outside temperature.