Less is More

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Turn it down. Turn it way down.

I’m referring to the pressure setting on your steam system. The single easiest thing you can do to improve the performance, comfort and fuel economy of your steam heating system is to reduce the pressure. It should also be the first thing you do when things aren’t working right.

It’s tough to do. It seems counterintuitive. That back addition or attic bedroom isn’t getting enough heat, so it seems to make sense to turn up the pressure to force the steam into the far reaches of your system. But it seldom works. And what’s worse, it usually creates even more problems.

Most of the components in your steam system operate best within a range of pressures. Take main air vents, for instance. They come in lots of shapes and sizes AND pressure ranges. I was recently in a home with end-of-main vents that weren’t working properly. They seemed to vent OK at the beginning of the cycle, but appeared to stop working before the main was completely vented.

As it turns out, these particular main vents are designed to operate at less than 3 PSI. At higher pressures they close off tightly ­— rendering them essentially useless. A check of the pressure control had the system set at 7 PSI. So as the steam pressure rose inside the pipes, the vents worked until the pressure got to 3 PSI, then they’d stop venting. Since this was a one-pipe system, the radiator vents had to do double duty venting the rest of the main, all of the risers and the radiators.

A standard Honeywell Pressuretrol

This meant the radiators farthest from the boiler were not getting much heat. By the time the radiator vent in the attic allowed steam in, the radiator in the dining room (where the thermostat is located) had been full of steam and heating for some time.  It satisfied the thermostat and shut the boiler off just as the attic radiator was getting started.

When I turned the pressure down at the boiler, the main vents were able to completely vent the mains and allow the radiator vents to get back to work, venting only the risers and radiators. That’s when the attic radiator finally got some steam and heated the previously unusable attic space.

 

It can be worse on a two-pipe vapor system, as this usually has just one vent at the end of the dry return. If this single vent shuts off on pressure, everything stops heating. But the boiler keeps firing, trying to raise the pressure — wasting fuel.

A Honeywell Vaporstat

So what pressure is right for you? I haven’t met a residential space heating system yet that needed more than 2 PSI. And many need even less. In fact, on most of the replacement boilers I install, I routinely discard the factory pressure control that comes with the boiler and replace it with a Vaporstat. The factory-supplied device can only control the pressure down to 1PSI.  A Vaporstat regulates the pressure in OUNCES, which allows me to control the system at LESS than one pound of pressure — usually between 4 and 10 ounces. This can save a significant amount of fuel while improving comfort AND system performance.

Heidronically yours,

Wayne