Steam Radiator not staying HOT long enough

Old 12-13-19, 04:21 PM
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Steam Radiator not staying HOT long enough

I live in a 4 story Apartment building with a Steam Boiler system that works with a Heat Timer Model EPU Blue Control Box . The Boiler recently broke and when they fixed it I noticed that my Radiators that feed off the risers were not getting HOT fast enough and were not staying HOT enough like they did before the Boiler broke. The cycle is set for 45- 50 minutes (or at least it used to be) Now my riser is piping hot for the entire duration of the cycle, but my radiators are only hot for 20 minutes of the cycle which is not enough for my apartment to retain the heat and have had to resort to using a space heater. So my 1 riser gets hot for the entire duration of the cycle but my radiator does not. The vents are fine on my radiators so there is something off on the timing or connection of the radiators. Also the setting of the EPU blue box are set to the highest and nothing changes. Whereas before the Boiler was repaired. The temp setting were much lower and the radiators were piping hot for the entire cycle. The plumber came and said my radiators were fine and Boiler people said the Boiler is fine... but, I who have lived in the apartment for 30 years know that something is different. Any idea what could be the problem? Thanks
Night Thermostat

Indoor Element Adjustment (determines “Heat Circulation Established)

(Adjust to “X + 2” if direct acting pressure switch is used on EPU only)

MODEL EPU-CH And MODEL EPU temperature Heat Timer Model EPU Blue Control Box
Old 12-16-19, 08:52 AM
Join Date: Mar 2010
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Were any new valves or any electrical or electronic controls added to the radiators or steam pipes within your apartment? If so, where were they put?

Do all radiators in the apartment get to nearly the same temperature before the boiler shuts down and the riser cools down?

Is one radiator in the apartment noticeably cooler than the others, which suggests a problem such as a clog in that radiator?

(edited later) The riser stays ultra hot because it has to remain at near 212 degrees F for steam to pass on through to the radiator(s).. Otherwise the upcoming steam will condense in the riser and immediately fall back down to the boiler (which it does during the first several minutes of the boiler "on" cycle)..

When the steam finally reaches the cold radiator, it will condense there until the radiator gets to near 212 degrees. Because the interior of the radiator is a cavernous space with a lot of interior metal surface area (essentially the definition of radiator) compared to the riser, it will warm up very slowly. The cycle has to run long enough for enough steam to enter the radiator to get that piping hot.

Almost all of the heat is from the act of the steam condensing inside. The "hot water" that the steam condensed into contributes less than 5 percent of the room heat as it drains out of the radiator and flows back to the boiler.

When some radiators approach 212 degrees, steam will remain uncondensed inside them and additional upcoming steam will be diverted to other radiators due to the (minute) pressure buildiup in the risers just before the already hot radiators.

A problem with systems such as from Thermal Inc and Heat Timer is that some parts of the building will get oversupplied with steam or forced hot water before other parts get enough. I dare say you have an administrative problem whose solution should, here, start with a much longer cycle and perhaps a higher boiler temperature (if the system employs temperature selection) and then gathering data to see which radiator(s) are last to heat up and put the system-satisfied sensors at those radiators.

Another refinement is remote controlled cutoff valves at radiators that heat up sooner so those radiators don't get serviced for the full length of a cycle that barely manages to serve some of the other radiators.

For now you will have to avoid opening windows to get fresh air although you might be able to leave the front door open to a corridor to exchange room air with corridor air.

Last edited by AllanJ; 12-16-19 at 11:18 AM.

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