New Steam Boiler Short Cycles
Dan replies: The problem you’re having here is a direct result of your having missed Mass for so long. I figure you’re being punished.
But then again, it could also be coming from a too-slow venting rate. At the end of the dry return, near the “cast-iron ham” (which is actually a boiler return trap — an old mechanical version of a condensate pump), you will find a central air eliminator. On top of that central air eliminator is an air vent. Now, this may not look like an air vent, but don’t let that fool you. It may be very small — nothing more than a screwed, brass fitting that contains a metal ball. You’ll find a drawing of the device in Chapter 15 of Lost Art. Once you find this vent in the old church, take the cap off and remove that metal ball. You don’t need it unless you’re burning coal. The ball helps create a vacuum, which can screw you up when you’re burning oil or gas. If the air isn’t leaving the system quickly enough, the boiler will short cycle as well, and that’s why I want you to check that air vent.
One bad steam trap, anywhere in the system, can also make the burner short cycle on pressure. Poke around and make sure all those steam traps are working.
Next, check the size of the boiler against the connected load. The boiler’s ability to produce steam has to match the system’s ability to condense steam, and vice versa. If the boiler’s too big, it can short cycle.
Widen the pressure differential on the vaporstat a bit. Try a cut-in setting of 4 ounces, and a cut-out setting of 12 ounces. And make sure you’re setting the differential properly on that Vaporstat. The control may have a “subtractive” differential, in which case you would set the “Main” scale to 12 ounces and the “Differential” scale to 8 ounces. That will give you a range that has the burner cutting in at 4 ounces and cutting out at 12 ounces. “Subtractive” means you set the high point first, and then subtract the differential to get to the low point.
Wood Floors And Radiant HeatAre there pitfalls when implementing radiant floor heat with wood floors in new construction? I hear a lot of discussion about this and I’m not sure what to do. Please advise.
Dan replies: There are some things you need to watch out for with wood floors and radiant. First and most important is that the wood must be dry — not more than 6 percent moisture. You can check this with a moisture detector, a device you should own if you’re going to do this sort of work. Next, with radiant, the finished floorboards shouldn’t be wider than 3 inches. Laminated wood works better than hardwood because it does a better job of expanding and contracting without doing damage to itself.
If the floor is going over concrete or gypsum concrete, make sure that stuff is dry before the carpenters put down the finish wood. Also, watch out for the painters and the plasterers. Their work can add a lot of moisture to air in the house. Provide ventilation during construction so that the moisture can get out as quickly as possible.
If you’re putting the tubing in a joist bay, the floor will heat most effectively if you use the aluminum plates that attach to the bottom of the floor (see the Wet Head Gazette, January 1998, in my website for specific information on this). The tubing snaps into these plates. You have to leave at least a 2–inch air gap between the tubing and the top of the insulation. The foil face of the insulation must face upward toward the tubing. You will have to run hotter water though the tubing (compared to a concrete floor). The wood doesn’t hold as much heat as concrete.
Those are the high points. I just finished a book on this subject. It should be available in May. Check back with me then.
Steam Shows Up At The Condensate PumpSteam is getting into the condensate tank on this job I’m working on. It’s a new installation at an old Navy base. I looked at the near-boiler piping, and it all looks to be as it should. Dan, this is an old system and we repaired all the steam traps on all the radiators. We also replaced the float and thermostatic trap by the drip leg at the end of the main.
The system is two–pipe with a 2 1/2–inch main and a 1–inch return. There are 18 radiators. The F&T trap is piped off the last leg that goes up to the last radiator. I have four radiators shut off right now while I’m waiting for repair parts. All the return lines are cool where they meet the main return, but right after the F&T trap, the pipe gets hot. This F&T trap is rated for 30 psig, and I got the system heating like a champ with just 1/2–psig pressure. We changed the pressure gauge at the boiler to read 0–15 psi so that we could better see what’s going on.
Is there anything we missed? My boss is thinking about adding another F&T trap to the condensate line, just before the condensate pump. I’m thinking the problem has to be somewhere in the piping. What are you thinking?
Dan replies: I’m thinking that the last thing I would do would be to add that “master” trap near the return pump. If I did this I’d be double-trapping the return lines, and that would really screw up the system. Condensate would back up into the main and I’d get water hammer.
It sounds to me like there’s something wrong with that F&T trap. You should have a 15–psi trap, since it’s on a low-pressure system. Steam is obviously passing through, and that might mean there’s a busted thermostat in that trap. Since there’s no temperature drop across an F&T you’ll need to pop open a union, or whatever, right after the trap to see what’s coming out of it.
Walk through the system piping and ask yourself, “If I were steam, would I be able to cross into the return anywhere along the way?” “Think” like steam and you’ll come up with the answer. This one sounds like piping, for sure. Don’t let your boss add that extra trap. Tell him he’s a knucklehead. See what he does.
How Can This Work?I was called to a job for a coil-plate leak. When I got there I found a Federal scotch-marine boiler. This boiler makes low-pressure steam. They’re running it at 7 psig right now. The boiler has two inverted tankless coils, and they called me to repair one of them. Both coils heat a large swimming pool.
The steam comes from the boiler’s 4–inch nozzle and rises about 4 feet above the boiler before turning toward the wall where in enters a steam-to-water heat exchanger. The exchanger has two Hoffman air vents installed in the top. The water side of the heat exchanger heats the building through some fan-coil units. The condensate leaves the heat exchanger through a 1 1/2–inch line, dropping straight to the floor before working its way around to the back of the boiler. There’s no steam trap, condensate pump, equalizer or Hartford Loop. The condensate just goes right back into the boiler.
The way I see it, this system shouldn’t work, but apparently it does. The head custodian says every once in a while he has to “drain” the exchanger, and then he gets heat. Do you think this should work?
Dan replies: The air vents should be on the outlet side of the heat exchanger’s shell, not the inlet. The steam has to be able to push the air through the exchanger, not just up to it. Vented this way, the air can get completely out of the exchanger. This goes not just for heat exchangers, but also for fan coils, or anything you heat with steam. You vent at the outlet, not the inlet.
If you vent the top of the heat exchanger itself, the steam, being lighter than air, will head right across the top of the exchanger’s shell and shut the vents before all the air can escape. Some of the coil will always be air-bound, and that’s probably why they have to run such high steam pressure. They are essentially compressing the air into the return line, which is probably why the condensate can’t drain fully back to the boiler. Prove it by popping open a union (or something) in the condensate drain line. See what happens, and then smile like a hero, my friend.
Also, if there’s no vacuum breaker in that shell, add one. When the steam condenses, it shrinks. If air can’t get back in because the air vents are still closed on temperature, the condensate won’t drain from the exchanger. This can lead to water hammer damage to the heat exchanger’s tube bundle.
‘I Have One Word For You, Benjamin. Plastics!’A story I thought you might like. I work for a major plumbing supply house in northern New Jersey. This job permits me to see and hear some of the best industry talk around. One day, a contractor came in and said to me, “You gotta hear this story!” He bid on a steam boiler replacement for some lady. The lady told him, “No thanks. Goodbye.”
But then she called him back a week later in a panic. “You gotta come right away!” she says. When he gets to the job and goes down the basement he walks right into a steam bath! There was steam and condensate everywhere and the pipes were sagging like wet noodles. He shut the boiler off right away, of course. It seems that whoever piped the boiler did it in PVC pipe! PVC pipe on a steam boiler!
The contractor asked the lady why she hadn’t used him instead of the other guy. She could have gotten the job done right the first time around. Now she was going to have to hire him after she had already paid the other guy. “But the other guy was a thousand dollars cheaper than you,” she said.
”Lady ... didn’t you ever stop to wonder why?” the contractor asked.
Dan replies: And people accuse me of making this stuff up. I couldn’t possibly make this stuff up. And as long as guys like you keep writing to me, I won’t have to!
Father Of The BrideYou got me, Dan! I remodeled my kitchen (because my youngest daughter is getting married), and I decided to install radiant heat instead of a kick-space heater. It worked like a charm. It is quiet. It heats the room without anyone knowing that it’s even there. However, I can now understand why some contractors don’t want to install it. There are too many options, and they have to get involved with other construction trades, which may make them nervous. They have to become carpenters (or at least lay out the job for the carpenters!) They also have to know how to do masonry work. These are limiting factors for many P&H guys. They either don’t want more work, or don’t understand that they can get paid for this work.
I used the Comfort Panel system, where you nail down 1/2–inch plywood panels that are grooved to accept the tubing. The finished floor goes over the panel (I was putting down a new floor anyway). This installation method is a lot easier than staple-up.
Dan, since you are all-wise in these matters, I do have one question. What does remodeling the kitchen have to do with my daughter getting married? My wife says that this is just the way it is, but I still don’t understand.
Dan replies: I hear lots of good things about those panels. I’m glad you gave radiant a try, and I hear what you’re saying about the other trades. There will always be contractors who resist change, but that only means there’s going to be more opportunity for the ones who choose to grow.
As for the women, don’t try to figure them out.