One pipe steam and recovery from night setback

David Nadle

Something's not right

philc, it should take nearly the same amount of time to fill all your radiators on a moderate day as on a cold day. And that time should not be 90+ minutes.

Your low pressure gauge not registering over an ounce suggests to me that your pigtail is probably clogged. Your gauge and vaporstat are likely not seeing the true pressure, which explains the long cycle. Alternatively you can check it with a homemade manometer connected to a drain coupling; do a search on the Wall and find my manometer thread. The other explanation for why you don't build pressure is too horrble to contemplate.

In my case I think adjusting the firing rate is turning the wrong knob. It takes 20+ minutes of steaming to hit 11 ounces on the first cycle. That doesn't seem "overfired" to me. The fact that the subsequent on cycles are so short tells me that there is a large pressure gradient through the system, with a vacuum developing at the boiler, while the rads and mains are still under pressure.

If I have time tomorrow I'm going to try a new delay relay configuration.

Phil_17

It's perfect from my point of view...

Hi David,

Why do you think it should take less than 90 minutes to fill all the radiators? How many should it take? 60? 20? 10? As far as I know there is no magic number that I've ever seen written down. In my home most heating cycles have the thermostat satisfied before they are even filled half way. Coming out of an overnight set back (generous 6 degrees) there are still a couple that don't fill all the way. They don't NEED to.

My house is OLD, the radiators were sized for the load back in ~1890. I've replaced all the drafty old windows, and had icynene sprayed into the attic and walls. My heating load is way lower than the radiation was designed for... thus there is virtually never any time that the radiators need to be filled all the way across (multi-day long power outages with outdoor temps in the 20's is the only one I've encountered so far).

My system works great for me year round; I have no hissing vents, no spitting water, no hammer, super low water consumption (I need to add boiler water about twice a year), it heats evenly and does not overshoot the thermostat. It does this without ever cycling on pressure. The boiler (a new MegaSteam) is only about 16 months old, and there is nothing wrong with either the pigtail, the gauge, or the controls.

Since there is so much discussion on this board about cycling on pressure, short cycling, etc. I was beginning to wonder if perhaps my boiler was underfired because it never cycled on pressure. I replaced the pressurtrol with a vaporstat and added the low pres gauge at that time. Keeping a close eye, the gauge typically shows less than one ounce of pressure and this is more than enough to heat the house very nicely. Sometimes near the end of a long cycle (setback recovery) I had actually seen it rise all the way to TWO ounces. After a long time thinking about it, I have concluded that my firing rate is just fine (perfect in fact) and there really is no need to have it any higher. My house heats fine. My fuel consumption is reasonable for where we live, the size of the home, and all the rest. There is no need for more pressure in the boiler, since what matters is the difference in pressure between the boiler and the radiators. With mains that are insulated almost all of the condensation occurs in the radiators (1700:1 drop in volume) which creates more than enough change in pressure (essentially a vacuum) to suck more steam in from the boiler.

I'm not a pro. I'm a HO who has spent several years lurking here, reading Dan's books, and experimenting with my own system. I like the way mine is working, and I think I have a good grasp on how it all fits together. My humble opinion is that you can fiddle with all kinds of relays, delays, and other control strategies but you won't find satisfaction while a fundamental issue remains unaddressed... I maintain that lowering the firing rate will fix your problems, and maybe even save a little bit of fuel in the process.

Enjoy!

-Phil

David Nadle

Sounds good.

Maybe I misread what you wrote. I took 90 minutes as indicative of a normal cycle time. They way I figure it time is money, and the faster you can fill the rads the less fuel you will burn. Whether you fill them or not isn't the issue. How long is a typical maintenance cycle?

Maybe your system was designed to fill at 1 oz., I don't know. I'm surprised that a system that can fill at 1 oz. takes 90 minutes to fill. I just know that I marveled at the 1 to 3 oz. pressures my system seemed to be filling at for a while, until I checked and realized that the pigtail had clogged sometime in the first four months of operation.

Clocking my gas consumption at the meter gives a figure of ~106,000 BTU/hr, which is right on target for a 112,000 BTU boiler. I don't get how trying a relay to compensate for slow return of condensate is "fiddling," but adjusting the firing rate off the manufacturer's spec is a no-brainer.