For steam...easy poor man's Heattimer---Minimum run-time relay

Mark Woll_2

First a little into: During the summer, I replaced a 600,000 btu Weil-McClain steam MGB5 with a 375,000 btu Weil MClain LGB4, and guys, this house hasn't seen such nice steam since the days of the Dead Men. Half a psi! I swear Holohan and the geat guys who helped me on the Wall with initial design are geniuses. Took the liberty of totally rebuilding the boiler room for this 6000 sf house.

We took a single 4 inch off the boiler, sent it up to a brand new 4 inch drop header, took off two 4 inch drops which were in turn bushed up to fit two brand new 6 inch flanges which where fitted to the existing 6 inch main. Naturally all fitting were cast iron, no malleable in that header!, and all pipe was threaded steel. You should have seen the copper garbage we took out.

Let me say that plumbing isn't steamfitting.

Added a vaporstat, added another, "alternating" boilerfeed pump (now there are A and B pumps which alternate every other cycle and which provide backup in case the primary fails). Before, the single pump had failed in the middle of the winter, natch.

Added a "minimum run time relay" which is the point of this thread. We all know that steam systems need time to build up a head of steam before the heat arrives. It seemed that no matter how the thermostat is adjusted, these new programmable digital jobs were just too damn sensitive for a steam system! It tends to short cycle because the first floor where the thermostat lives is heated first. I tried relocating it once, but I got tired of experimenting and drilling holes in plaster walls.

In apartment buildings they sometimes forget the thermostat and use a Heat-timer which is an elaborate computer which measures outdoor temperature and among other things has a most distant radiator heat sensor. The idea is that there's no short-cycling as the Heat-timer knows when it's filled with steam. Once filled, the unit's runs and rests are based on a computer controlled off/on "curve" dependent primarily on outside air temperature and the signal from that most distant radiator sensor. Price?? about $3,000.

Well I thought, maybe I can cheaply do virtually the same thing. I figured usually the time it takes to fill the system is about the same (except first thing in the morning), so I installed a time delay relay (I set it in this house to about 35 min.) which is triggered by the closing of the thermostat contacts. The time delay merely jumps the thermostat contacts, so the boiler still operates even if the thermostat is satisfied. (I also installed a remote reset switch by the basement stairs to interrupt the relay if needed.) For mornings it's still perfect even with cold pipes, since the thermostat controls the run, and keeps the unit humming even after the relay's program lapses.

Does a perfect job!!

Just to prove i'm a wiring geek, now the boiler control relay box has a total of 3 time delay relays, 1 alternating relay, and 1 "regular" relay used to issolate the the thermostat wiring. See wiring diagram below if you're a masochist.

Anyhow, it seems to work great, even on the last 7 degree F day or two.

Dale

Safety comment

The steam boiler is designed to shut off in normal situations by the stat, then if too much pressure the pressuretrol. This is what is shown in the install instructions. I don't know how much you trust your time delay but if you are a belt and suspenders type a high limit stat set to perhaps 75 or 80 degrees might be a feature to add to your time delay jumper output.

Mark Woll

hmmmmm

I'm not sure I agree, Dale. In my opinion, the pressure controls modulate the pressure to keep it properly in the system's optimal specification. Here, I run the vaporstat to control the system at about .5 psi (8 oz.) (this system being a commercial-sized boiler also has a secondary pressuretrol set at about 1.5 psi which operates only if the vaporstat fails). The thermostat is set at the ordinary room temperatures required (65 night, 67-68 daytime). The pressure controls don't control the temp in any fashion, they just modulate the pressure. Depending on how cold the pipes are, this modulation occurs during the time period when the thermostat calls for heat.

I suppose it the time delay relay failed in the closed position (an unlikely event, but not outside the realm of human existence), the unit would operate indefinitely and overheat the house, but the same thing would happen if a thermostat failed.

Mark