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Old 11-27-2008, 11:38 PM   #1
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Baseboard radiator question


My home has a single zone hydronic baseboard heating system. The copper tubing and the baseboard radiators are all 3/4". My kids destroyed the fins on the baseboard radiator in their room. I have a new 1" baseboard radiator. If I replace the 3/4" radiator with the 1" in their room will it affect system performance?
Thanks for any help.

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Old 11-28-2008, 12:40 AM   #2
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Baseboard radiator question


The answer is Yes and No, with the No kinda winning out in the end.

Basically, a bigger radiator (with larger fins) full of the same temperature water is going to convect more heat into the room than a smaller radiator will. So, you'd expect the room will be warmer than it should be.

However, most DIY'ers won't know this, but every HVAC contractor will know that a house like yours would need "balancing valves" to prevent all the heating water from taking the easiest path through the shortest radiator loop in your house, leaving most of the house cold, and one or two rooms too hot.

Basically, everything but the longest radiator train will have a balancing valve (which will typically be a gate valve) that will be left partially open to pinch off flow through that loop. The more loops, the more balancing valves, and the valves on the shorter or less tortuous loops will be closed more than the valves on the longer loops are, thus offering similar resistance to flow through all of the various radiator loops in your house, and a uniform temperature throughout the space.

In your case, you would need to pinch off the balancing valve on that loop a bit more to allow less water to flow through it. That WOULD result in that large radiator convecting less heat, but all the other radiators on that train would convect less heat as well. Whether or not the effect would be noticable is a SWAG (Scientific Wild Assed Guess).

In this case, if it wus me, I'd probably just straighten out the fins on that rad as best you can with a pair of sheet metal working pliers, and then buy a cover for that rad to prevent an encore performance by the kidz. Or, if you choose to replace the mess, I'd probably replace with another section of 3/4 inch radiator.

If you do this, replace an elbow at the downstream end of that radiator train with a tee instead of another elbow, and solder in a 3/4 by 1/8 NPT bushing into the top arm of the tee. Screw a short brass 1/8" nipple into that bushing and screw a 1/8 inch ball valve onto that nipple. Use pipe dope or teflon tape on both ends of the nipple, but not on the air vent you screw into the ball valve.

That way, most of the time you can have an air vent on that ball valve and use it to bleed air out of your heating system. However, if you ever drain your heating system for repairs, you can save the old water in 5 gallon pails and siphon it back into your heating system afterwards using a 1/4" X 1/8" NPT hose barb screwed into that ball valve (if you can release the air pressure somewhere else that would build up in your heating system as the water level rises).

Some people would scoff at that idea, but if you add new water to your heating system, you're also adding new dissolved oxygen and new hardenss ions. The new dissolved oxygen will end up forming rust in your iron boiler and the hardness ions will end up forming scale in the hottest part of your heating system, namely the boiler again. Putting the old oxygen depleted and ionically dead water back into your heating system is healthier for it than changing the water in your heating system.

Of course, the above assumes that your boiler has a lower elevation that the radiator we're talking about.

Hope this helps.

PS: Automatic air vents are a pain because they often stick open. So, after draining your heating system, a stuck open automatic air vent can cause water damage to a wall or ceiling if it sticks open when you're refilling your system. Stick with manually operated air vents.


Last edited by Nestor_Kelebay; 11-28-2008 at 12:44 AM.
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Old 11-28-2008, 04:18 AM   #3
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Baseboard radiator question


That room will get more heat then it use to.

How much more, depends on its rating, and the rating of the old baseboard.

One simple solution, is to close the baseboard damper a little, if your system is a single loop system.
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Old 11-28-2008, 03:15 PM   #4
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Baseboard radiator question


One thing we may be forgetting is the affect on the rest of the radiation in the system. Any room downstream of the new radiation may not heat as well. If the new radiation has more of a btu output than the old radiation. How many btu's are being removed in a 3/4" pipe"
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Old 11-28-2008, 05:42 PM   #5
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Not as many as in a " element.

Some 1" baseboards, are only 100 to 200 BTUs per foot more then ".
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Old 11-28-2008, 11:43 PM   #6
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Baseboard radiator question


Thank you all for the replies. The only reason I wanted to use a 1" radiator is because I already have it on hand. I may just buy a 3/4" replacement with all the covers.I was going to make a new register out of wood so the kids couldn't destroy it again. I tried to straighten the fins. But didn't have very good luck.
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Old 11-29-2008, 05:00 AM   #7
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A few nights in a cold bedromm, will keep them from destroying the new baseboard.

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