So this fella comes up to me after a hot-water seminar and tells me about a problem he's having with this copper-fintube baseboard loop he installed in this big hall with a bunch of offices. "I can't get the end hot," he said.
"What have you been doing?" I said
"I've been purging it every day," he replied.
"How's that working out for you?" I asked.
"It’s not. If it was working out for me, would I be talking to you?"
“I guess not,” I said.
“So what am I supposed to do?” he asked.
What size is the fintube?" I said.
"It's three-quarter inch. That's all I use," he said. “I like three-quarter baseboard. I can always get it from my supplier. I use it all the time. It pays to settle on one size fits all when I can. Three-quarter works on every job. But not on this one. Why do you think that is?”
"How many feet of element do you have on the job?" I asked.
“The whole thing?” he questioned.
“Yes,” I replied.
"All in all, I’d say it’s about 400 feet," he said.
“How many zones do you have?” I asked.
“Just the one,” he said. “That’s what the customer wanted. One thermostat for the whole place.”
“You have nearly four hundred feet of three-quarter fintube on one zone and you’re asking me why it’s cold at the end?” I said.
“Yes. It’s more lukewarm than cold, but you know what I mean. It’s not hot enough to heat those end offices. Why?” he replied.
"I’d say you ran out of heat," I said.
"How could that be? The pump is running. So is the boiler,” he said. “Everything is doing what it’s supposed to do except the baseboard. It just won’t stay hot."
"Okay, let's try this," I said. "I want you to imagine a British thermal unit as a tiny man with a trench coat, a bowler hat, an umbrella and a briefcase. He's British. He lives in the boiler and he works in the baseboard. He travels to work on a train that we'll call 'flow.’"
“You mean like the water in the pipes is the train?” he asked.
“I like that," he said. “It’s like a cartoon.”
Who doesn’t love cartoons?
"Okay, you can only get so many of these guys on the train because of the size of the pipe,” I said. “And the train’s not compressible. Make sense?”
“Okay,” he said.
“A three-quarter-inch pipe will carry about four gallons per minute tops,” I said. “If you try to force more than that through a pipe that size it will whistle. That's why the baseboard manufacturer rates the three-quarter-inch fintube output at 4 GPM and no higher. Four GPM delivers about 40,000 Btuh."
"Okay," he said.
"So all the Btu guys get on the train and head off to work. Think of each linear foot of baseboard as a train station. The train doesn't stop, though; the Btus just hop off. They can do that because they're tough little guys."
"How many get off at each station?" he asked.
“About 600 of them,” I replied. “That’s the Btuh output of your baseboard at the temperature you’re using. So when the train gets to the 70-foot mark, you're basically out of guys. They all got off up the line. Your loop runs on for another three-hundred and thirty feet or so from what you’re telling me, but with hardly any guys riding that train. You could probably chill meat with what's at the end of that fintube."
"You make that so easy to understand!" he said. "It's like a cartoon. Little guys going to work. I love it."
"So you know what you have to do now, don’t you? And here I figured he should be thinking about a bunch of shorter, individual loops coming off a manifold."
"Yeah," he said. "I gotta get a bigger pump."
“A bigger pump?” I said.
“Yeah. Much bigger.”
"There's nobody on the train," I said. "And you want to get them there faster?"
"Huh?” he said.
We went over it a few more times until he got annoyed with me. He didn’t want to have to re-pipe the job. That would have cost him too much money. And I was telling him something that went against a piping habit he had had for a long time. It's easy to run baseboard radiation from wall to wall to wall, but when you step over that 70-foot limit with three-quarter inch fintube, the little guys with the bowler hats will sit back and laugh at you as you purge your days away. What he did so often on smaller jobs would never work on the bigger jobs. You can't argue with physics, but he was willing to keep trying to do just that.
Here’s another baseboard cartoon for you. Where I live, we have what we call The Long Island Heat Loss Calculation. It works like this: If you have a 10-foot-long wall, it gets 10 feet of baseboard. No question about that. And if you have a 15-foot wall, it gets 15 feet of baseboard. Now here’s the best part: If a 10-foot wall should meet a 15-foot wall in a corner (lots of corners around here), that room will get 25 feet of baseboard, regardless of the room's actual heat loss. We put baseboard everywhere except where there are doors because baseboard manufacturers don't make them with hinges. Physics has nothing to do with any of this. It's a cartoon where installation is a breeze but everything else often gets screwed up.
In 1950, our house had a radiant floor, which lasted until 1970, and then 200 linear feet of baseboard arrived to replace it. Over the years, salesmen have cold-called to offer me great deals on heating equipment and fuel oil (there’s no natural gas in this neighborhood). I always invite the sales guys to stop by because I’m a writer and every one of those guys shows up with a delicious method of calculating the size of a replacement hot-water boiler.
My favorite method is The Long Island Heat Loss Calculation. It begins with the guy telling me we have a very nice house and plenty of baseboards. He then says that a boiler has to support the baseboard. One described it as being like alimony in a broken marriage.
I liked that. It’s cute.
That guy took out a tape and measured the total linear feet of the installed baseboard. He multiply that by 600 Btuh per linear foot and then give me an estimate for a 120,000 Btuh boiler, even though the actual heat loss of our house on the coldest day of a Long Island winter is a mere 40,000 Btuh.
I asked him if he was sure about that calculation. He told me that he'd been doing it that way for many years and that it was always the right way to do it. “The boiler has to support the radiation,” he said. Nodded. Smiled.
"Why is that?" I said.
"Well, because it's there!" he said.
I ask such silly questions.
"When would be a convenient time for us to start the job?" he asked, going for the close.
"Never," I said.
But there is a bright side to our great lengths of baseboard, and you can make this work for you if you’re paying attention. Most houses have too much baseboard and that means that, if you size the new boiler to the actual heat loss of the house, the folks will be able to run that boiler at a lower temperature on most days. That opens the door to a modulating/condensing unit. Many heating people turn their backs on mod-cons when there's baseboard because they figure the flue gases won't condense. The return temperature is just too hot. But it there's too much baseboard, those flue gases will be smiling because oversized baseboard is similar to those old systems that have high-volume radiators. The other guy's mistake just might work in your favor if you're smart, but watch out for that maximum run of 70 feet on any one loop.
One last adventure for you. This was a quick solve. I looked at a problem job where one room in the middle of a baseboard loop system wouldn't heat. I looked into the cover and noticed that the installer had turned that room's baseboard element 90 degrees before soldering it. The solid side was horizontal and doing a wonderful job of blocking any convective movement of air in that room. The little guys with the bowler hats got off at the other stations.
Can you see it in your mind’s eye?