Baseboard: How Much Is Too Much?
So this hefty gent 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 says.
"What have you been doing?" I ask.
"I've been purging it every day."
"How's that working for you?" I say.
"If it was working, would I be talking to you?"
"What size is the fintube?"
"It's three-quarter inch. That's all I use," he says.
"And how many feet of element do you have?"
"All in all, about three-hundred seventy-five feet," he says.
"And you want to know why the end is cold?" I ask.
"You ran out of heat," I say.
"How could that be? The pump is running."
"Let's try this," I say. "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, works in the baseboard, and travels to work on a train that we'll call 'flow'."
"I like that," he says.
"Okay, you can only get so many of these guys on the train because of the size of the pipe. A three-quarter-inch pipe will carry about four gallons per minute max before the water starts to whistle. That's why the baseboard manufacturer rates the output at 4 GPM, which is equal to 40,000 Btuh."
"Got it," he says.
"So they all get on the train and head off to work. Each linear foot of baseboard is a train station. The train doesn't stop; the Btus just hop off. They're tough little guys."
"How many get off?" he asks.
"Each foot, about 600 of them hop off. So when the train gets to the 70-foot mark, you're basically out of guys. They all got off. Your loop runs on for another three-hundred and five feet. You could probably chill meat with what's coming out the end."
"You make that so easy to understand!" he says. "I can see it all in my mind. It's like a cartoon. Little guys going to work. I love it."
"So you know what you have to do, right?" And here I figure he should think about how to pipe the shorter, individual loops.
"Yeah," he says. "I gotta get a bigger pump."
"There's nobody on the train," I say, "and you want to get them there faster?"
I went at it again until he got annoyed with me because I was telling him something that went against the habit he had built like a brick wall years ago. It's convenient to run baseboard radiation from wall to wall, but when you step over that 70-foot limit, the tiny guys in the bowler hats will sit back and laugh at you as you purge your days away.
You can't argue with physics.
Well, actually, you can, but you won't win. Ever.
The Long Island Heat Loss Calculation
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. If you have a 15-foot wall, it gets 15 feet of baseboard. 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 all about His Majesty, The Baseboard. Just can't get enough of it.
In 1950, our house had a radiant floor, which lasted until 1970, and then 200 linear feet of baseboard arrived. It runs off to a vanishing point on the horizon.
Over the years, salesmen have called to give me a price on a new boiler. Each measured our baseboard, multiplied each foot by 600 Btuh, and then quoted me on a 120,000 Btuh boiler, even though the heat loss of our house on the design day is a mere 40,000 Btuh.
I ask each salesman if he is sure about the number. He will always tell me that he's been doing this for years and that he is certain. "The boiler has to support the radiation, you know," they say.
"Why is that?" I ask.
"Because it's there," they say.
"Would you like to sign here?" they ask.
Too Much Baseboard?
If a house has too much baseboard (and most do), that could be good news for you when you're selling a boiler because you'll get to run that boiler at a lower temperature, which opens the door to a modulating/condensing unit. We often turn our backs on mod-cons when there's baseboard because we figure the flue gases won't condense. If there's beaucoup baseboard, though, those gases may be loving it because it's 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 room in the middle of a baseboard loop system wouldn't heat. How come? The installer had turned that room's baseboard element 90 degrees before soldering, effectively blocking the air passages. Gosh.
Standard baseboard may not be the best choice for bathrooms where there is moisture (of all sorts) flying through the air. Steel will rust and be unsightly, even though it's factory-painted. Go with a non-ferrous type of cover for the can.
If you're getting expansion/contraction noises, check those plastic runners under the elements, as well as the size of the holes where the pipes move between rooms. Pipes grow wide as well as long when heated.