Crank It Down?
In 1989, when we started our business The Lovely Marianne asked me what I was going to do to make money for her and our four daughters. I told her I was going to write books but that it would take some time to do that. Then she rolled her eyes and asked what I would do in the meantime. I said that I would look for people who were rich, cold and miserable and consult with them on their troubled heating systems. I promised to be irresistible.
“Where are you going to find those people?” she said.
“They’ll find me,” I said.
And they did because I had studied old steam systems and not many people in this business had taken the time to do that. I wasn’t going to actually touch any of those systems but I would write good reports that the RC&M could then show to any contractor, and I would charge appropriately so that they would respect my advice.
Most of the time, the problem had to do with the steam pressure being too high. Older steam systems are supposed to run on ounces of pressure, not pounds. But when an air vent gets clogged the steam stops moving. That’s when some knucklehead steps in to crank up the steam pressure. It’s very easy to do that. All it takes is a screwdriver and an empty head.
Often when I was consulting all I had to tell the RC&M person was that the pressure was much too high and he needed his contractor to crank it down. Oh, and replace the clogged air vent. My hands would be in my pockets as I said this. They would nod, smile, and pay me.
As time went by, Crank it down! became the three most-profitable words in my vocabulary. I knew from reading lots of old books that if you do that most steam systems will work because you are putting things back to the way they were meant to be in the beginning. I did seminars all over the country and I preached Crank it down! until people went out there and did it.
But then one day I got hired to look at a steam system in a big warehouse. The steam main was near the ceiling and the takeoffs from the main fed downward to a bunch of unit heater. Each unit heater had a bucket trap at its outlet that discharged upward to the condensate return line, which was a few inches lower than the steam main. I figured the steam pressure had to lift the condensate about eight feet to get it up there to the return.
“What’s the problem?” I said.
“The unit heaters stopped working,” the guy who hired me said.
“What pressure are you running?”
“Two-psi,” he said.
“That’s too low,” I said. “You need at least four-psi just to lift the condensate from the trap to the return. Why are you running the pressure so low?”
“We sent our maintenance people to this steam seminar a few months ago,” he said. “The guy doing the class is an expert on steam heating. He kept saying we should crank it down. So we did.”
“That was me,” I said.
“That was you? The seminar guy? Really?”
“Yes,” I said.
“Wow. So what should we do?”
“Crank it up,” I said.
And then I handed him a bill.
As in life, there are always exceptions to the rule. Here are a few places where you’re going to need more than a few ounces of steam pressure to get the job done:
When your condensate needs a lift. As I told the guy in the warehouse. Using steam pressure to lift condensate is a wasteful way of getting the job done, but some places just scream for it. That warehouse used overhead returns because the steam mains ran down the middle of the place and the floor was occupied by lots of stuff. There was no place to put a return main other than up top with the steam main. One-psi of steam pressure will lift condensate two feet, so we measure the vertical distance between the trap’s discharge to the condensate return line and divide that by two. That’s how much pressure we’ll need at the trap’s inlet. Oh, and we’ll need a bit more pressure to get the steam from the boiler to the unit heater’s inlet. How much you’ll need will depend on the load and the size of the steam pipes.
You don’t have radiators. Radiators will usually run on ounces of pressure, but if the job has air-handlers or reheat coils, you may have to crank up the pressure a bit to make them work. Check the manufacturer’s specifications to see what they call for.
You’re staring at a shell-and-tube heat exchanger. This gets a little tricky because you can bring any pressure you’d like to a shell-and-tube heat exchanger. The designer gets to decide that. In most cases, the higher the steam pressure is, the smaller the heat exchanger will be. The heat exchanger has to heat a specific load in gallons per minute through a temperature rise that the designer chooses. What that GPM, temperature rise, and steam pressure are won’t appear on the heat-exchanger’s nameplate, and that’s the challenge. It could be anything. The only way to know for sure is to have the plans and specs for the job. But you probably won’t have those so you’ll have to try different steam pressures and see what happens. The lower the better. The same thing applies to steam kettles in restaurants, but in this case the result is more delicious. The higher the pressure, the quicker the lobsters and crabs will get to your plate.
Smaller-than-normal distribution piping. Gerry Gill is a brilliant heating contractor who works wonders with steam systems in and around Cleveland, Ohio. Gerry created what he calls a Minitube System that is a joy to see. It works with very narrow pipes and higher-than-normal steam pressure. It’s quiet and fast and very efficient. It makes me smile because back in the ‘50s, Iron Fireman offered a similar system that they called Selectemp. This system also used tiny pipes and the fans in their wall-mounted heaters ran on tiny steam turbines. Gerry took Selectemp as his inspiration and made it even better with his Minitube System. When you look at stuff, it’s important to know what you’re looking at. If you’re not sure, ask.
And while we’re talking pipe size. I was looking at an old catalog that a unit-heater manufacturer published in the ‘50s. There were very specific instructions on what size pipe to use if you were supplying the unit with hot water, and a different set of instructions if you were using steam. The steam-piping spec called for larger pipe than what you needed for hot water. And because I am curious, I next checked the same manufacturer’s current literature for their pipe sizing. This, too, made me smile because they now show the same size pipe for steam and hot water. That means that if you’re going to use steam you’re going to have to use a lot more steam pressure to get though that undersized piping. The lesson here is that is something appears in a manufacturer’s catalog that doesn’t mean the person who put it there knows what he’s doing. Study. Think. Rely more on yourself.
More exceptions? Are you trying to add moisture to the flow of air by using steam humidification? This often needs a pressure higher than what you’d send to a radiator. That’s commercial stuff. Separate commercial steam from residential steam heating in your mind. They follow different rules. The boiler’s in your local dry cleaner’s store is high-pressure because high-pressure steam makes the iron hotter. You can’t use a low-pressure boiler in a dry cleaner’s shop. Well, actually you could but they’d probably go out of business.
Sometimes you just have to crank it up, but when it comes to steam heating in an old building, most of the time the solution will arrive if you go the other way. Crank it down!