Been thinking about the year 1970 lately. It started when this tune popped up in “shuffle” mode:
Let’s say you’re looking at a boiler replacement job in a house built when “Hitchin A Ride” was climbing the charts. There’s a 41 year old cast iron beastie in the basement that’s lived a good life and is ready for retirement. It’s connected to a boatload of fin-tube baseboard. Your customer has been online, and asks you if a high-efficiency modulating-condensing boiler would be a good fit.
What do you tell them?
Well, there’s a report out there on using high-efficiency modulating-condensing boilers with fin-tube baseboard. The Energy Resources Division of the Brookhaven National Laboratory conducted the study for the U.S. Department of Energy back in 2004 (click here to download).
Any guesses on what they found?
Here’s an excerpt from the conclusion:
“Condensing boilers can achieve energy efficiency benefits even when used in homes with common baseboard radiators by incorporating a reset control which modulates the water temperature supplied to the baseboards with outdoor temperature….with propane, 90% of the load can be met with condensing operation and with natural gas, 96%.”
Translation: When connected to fin-tube baseboard, a modulating-condensing boiler with reset will condense 90% of the heating season when burning propane, and 96% of the heating season when burning natural gas.
There is a caveat, however:
“This of course depends upon the oversizing of the baseboard convectors relative to the design load of the home and the excess air level on the burner.
Translation? If there’s more baseboard installed in the house than the house really needs (oh, like that never happens!), you won’t need 1800 water in the dead of winter. Oh, and don’t forget to make sure the burner’s tuned properly.
The 25-page report is pretty technical (most definitely not a Tom Clancy page-turner), and it’s pretty conclusive. Mod-cons and baseboard are a happy marriage.
If you’re going to retrofit, though, there’s one thing you gotta do:
Remember, the study says it “depends upon the oversizing of the baseboard convectors relative to the design load of the home…”
There’s only one way to know if the baseboard’s been oversized: conduct an accurate heat loss analysis of the home.
And there’s only one way to know how much more baseboard has been installed than the home needs.
Yep, a heat loss.
Start with one room in your 1970 shack. It has 25 feet of outside wall, and the forward thinking original contractor, while grooving on “Julie Do Ya Love Me” by Bobby Sherman, knew someday you’d be there replacing his aging cast-iron relic with a new, fancy-schmancy high-efficiency modulating-condensing boiler. And he did you the ultimate favor: he installed 25 feet of fin-tube baseboard, covering every inch of outside wall space.
At 500 BTUH/linear foot output, that’s 12,500 BTUH worth of installed baseboard at a 1800 supply water temperature. You, being a smart heating guy, whip out your laptop, open up your Taco FloPro Designer heat loss software (click here for free download) and run a quick heat loss on that room. You find that on the coldest day of the year, the room only needs 4,981 BTUH.
There’s 2-and-a-half times more baseboard in that room than you need if you were to run a buck-80 water temp. Being a smart heating guy, you do a heat loss for the rest of the house and find the same results pretty much everywhere.
If you only need about 5,000 BTUH for that room, and there’s 25 feet of fin-tube installed, simply divide 5,000 BTU’s by 25 feet to find out how many BTUH/ft you’ll need under design conditions.
5,000 BTUH ÷ 25 feet = 200 BTUH/ft.
Take a look at this chart from Slant/Fin and figure out what water temperature you’ll need on the coldest day of the year:
Sure looks like 1200 water to me – or maybe 1250, just to be safe.
In this scenario, the boiler will condense 100% of the winter.
Do the math. It pays.
Need another 1970 hit to stay in your head the rest of the day? Give this one a listen…
Yep, 1970 was one interesting year.
Filed under: Uncategorized