low pressure steam

marius

Hi All,
I'm working on an old victorian house that has about 15 or 16 radiators. originally the house had 140 btu lps boiler as the only source of heat. we had to pull that old boiler b/c it was too far gone. we but in a 106 btu lps boiler (burnham 406 i believe) in and hooked it up to the old system in addition to a brand new 120 btu high efficiency hot water boiler which we are running to radiant heat (under the floor boards) in most of the first two floors of the house. The third floor which is kind of a drafty/pitched roof attic space has three decent sized rooms and three accompanying radiators, but no radiant heating in the floors. Some of the rooms on the first and second floor have both radiant and steam heat.

All of the radiators/steam heat are controlled by one thermostat in the first floor hallway. All the radiant heating floors/rooms are controlled by individual thermostats in each room; five in total.

I have a few questions.

1. Is it feasible to turn off all the radiators on the third floor and just heat the first two floors by shutting off radiator valves on the third floor? Is it possible to turn off all the radiators on the second and third floor and only heat the first floor, by again, closing all the valves off to the second and third floor? Is it possible to tweek each radiator in the house individually to make some hotter and some cooler by adjusting the valves that individually feed the radiators?

2. If I run into the problem of the boiler kicking on too frequently or not frequently enough is this a problem I can solve by adjusting the psi on the Honeywell pressure sensor? Or am i locked in by the cubic volume of the pipe interior to btu out out put ratio? Could this potentially be mediated by shutting some radiators completely. A caveat here; the house had far less insulation before we started renovating it than it does now.

3. Having just read about this steam heating tragedy in NYC with the two children dying, are steam pressure relief valves designed to blow out of the radiator as a safety mechanism? the steam pressure relief valves i'm finding at the store now have threads that seem to be just a bit too small for the radiators in the house circa 1915. Is this intentional or do i need to find a conversion union that will make them snug?

4. Some of the pressure relief valves that fit into radiators are adjustable and some are not. Should the adjustable ones go further from the boiler? Should they all be adjustable in order to more finely tweek the system?


Just fired the boiler up for a minute for the first time after a month of retrofitting. Getting stoked. Thanks for the feed back !!

Jamie Hall

First things first. Is this one pipe steam or two? It sounds like one pipe, from your comments on "pressure relief valves" on the radiators... but we need to know.

If it is one pipe steam, then no, it is not a good idea to turn off radiators with their inlet valves. They never shut quite tight, and the small amounts of steam which do get in cause small amounts of condensate -- which can't get back out and causes odd noises, at best. However, you can effectively shut them off by turning the vents upside down. This prevents the air from getting out, and therefore the steam from getting in.

Second, those valves partway up the side of one end of the radiator are vents, not pressure relief valves. Their purpose is to allow air out, and therefore steam in. They come in various capacities, and the way to balance a steam heating system is to select or adjust the vents until you get the desired amount of heat from the radiator. Once you get the mains properly vented -- but that's another story. Adjustable vents are nice, but not all of them work all that well.

If the vents you are getting from the store don't fit the threads well, I would ask where you are getting them. The vents should have NPT threads, which are tapered; if they are too loose, they should just be screwed in farther. Some cheap vents from "big box" stores, however, have very poor threads. They don't make good paperweights, either. Get good ones.

Pressure from the boiler is controlled at the boiler, by the pressurestat control on the boiler. It should be set to turn off the boiler at around 1.8 psi and back on at about 0.8 psi. If you have the model number or a photo of the unit, we can tell you how to adjust it.

There should also be a pressure relief valve on the boiler. It is set to open at 15 psi, and you should never get anywhere near that. It MUST discharge through an open pipe leading near the floor. No if's, and's, or but's.

Steam boiler output is matched -- or should be matched -- to the total surface area of the radiators, termed the "EDR" rating. It has nothing to do with either the insulation of the house etc., nor with the volume of the pipes. If the boiler is properly matched, it should not shut down on pressure unless you are using a setback over about 2 or 3 degrees. Closing off some radiators will reduce fuel usage, but at the expense of cycling the boiler on and off more often.

You might consider buying the book "The Lost Art of Steam Heatinng" from either Amazon or this site -- it will really help you understand how steam heat operates.