Help with replacing radiators with baseboard units

We have an older house with a few hot water radiators in places we'd rather put furniture. I'd like to replace a few of them with baseboard heat. We have a single pipe system with each radiator fed off the "main" line and a circulation pump. The boiler runs about 170F.
This seems to me to be a relatively simple matter of properly sizing the baseboard and re-piping, but I'm always underestimating these things. Can anyone offer some advice? Is there a preference for cast-iron versus fin-tube baseboard units? Is there a simple way to predict baseboard size from radiator size?
Thanks, Tom
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I am definitely no expert in this area, but when I wanted to do the same thing (replace 2 cast iron radiators with baseboard heat), every plumber and plumbing supply house I spoke with said, "You can't mix copper baseboard units with cast iron radiators".
Apparently they do sell cast iron baseboard-style radiators, but they are extremely expensive. Also, there is some fomula they use that tells you how many feet of the horizontal baseboard-style units it would take to replace the heating value of each upright cast iron unit.
Bottom line for me was that I had a plumber replace two cracked cast iron radiators with similar sized used radiators that came out of an old house.

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Radiators are extrmely expensive, especially old ones. You can mix teh baseboards but you are going to have drastic temp swings. The heat value for cast base board is about 560 btu per foot. If you are going to do this why not remove the copper fin and just replace it with cast baseboard to, much more durable product.
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Thee is a web site from a plumbing supply house that has the information you need. I used it recently at work and do not have the information here. A google search may turn it up. You measure the radiator, count the sections and multiply for the answer. Simple to do.
Are you planning to keep some of the radiators? If so, you may have a balance problem witht he heat. Cast iron retains a lot of heat once the circulator turns off. Finned copper tubing does not. While one room is still basking in the warmth of the CI the other rooms will be cooled down more. You can buy CI baseboard. It would have roughly the same properties of heat retention as your present radiators.
There is information available here: http://www.burnham.com/radiator/58100.cfm I did not check it out, but they may have a conversion chart. http://www.burnham.com/lit/Baseray4-04.pdf
IMO, cast iron is the best heating system you can have. The only thing better than cast iron water is cast iron steam.
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Ed as usually you are right on the money with your repply, I am sorry I didn't read it before I posted, the only thing I think you are wrong about is CI baseboard can't scratch a you know what when compared with the Rads. It will though give himthe same BTU as the copper. This guy really has not given enough info to help him. How many zones, what is on each zone. When measuring rads it is a pain in the butt, you need how many sections, the width and length of each section, and the number of passes for each section. I can never figure it out I always call my Hydronic expert at my supply house.
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As others have said mixing units wont respond the same in overall comfort, your cast iron will retain heat for maybe an hour while even cast iron baseboard will be cooled of much earlier. This will lead to that room getting cool even while others are holding and radiating heat. Cast iron have alot of mass, water and release the heat slower.
I was looking at heating a room someone-a hack, removed the large 4 ft x5 ft x 14" cast rads and put in forced air water units for more furniture room, they never maintained even temps even though the Btu was there. When the boiler went off so did the heat but the cast iron kept warming for an hour. We got in real pro who pointed this out and indicated a separate zone with new piping, thermostat and pump would be necessary for him to guarantee comfort for baseboard or just put in the same cast iron as was in the rest of the house, we went with cast iron since this guy was a real pro that guarnteed his work in writing and did everyones work in the town. Yes we are happy, it works as originaly designed.
I dought you will ever be happy as the retention and slow heat release of large cast iron will not be the same as baseboard unless you run a separate zone, meaning piping, pump, and thermostat for baseboard. Sure you can match the Btu but it wont hold the heat and the room will cool faster when the boiler is not running, unbalancing your home.
Cast iron radiators sell for alot used and give great heat.
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Bob Pietrangelo wrote:

threaded copper adapters with cast/ malleable iron fittings in both Hydronic and Steam systems.
Corrosion doesn't seem to be nearly as bad an issue as one would expect. I'm no corrosion expert, but it may be due to the fact that these closed systems have little mineral and dissolved oxygen content.
Jim
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I thought you were saying it would provide proper heat. Sorry! Yes it is eaey to do we do boiler retrofits like that. I always tape and dope though.
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Sure you can. But what he was alluding to is the difference in performance. CI retains heat for some time. Finned copper cools rather quickly. You will have a greater temperature swing in the rooms with copper.
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7 yrs is a long time, a lawyer will tell you if you can persue it. How do you know if only a few had improper fastening, the ones you fixed. How can you check without ruining them
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Doobie, Under what premise can you mix the too, you can always make something fit, hell that is easy. What I was wondering is what principles are you using to make your statement that you can mix cu with ci.
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The two used cast iron radiators I bought weren't that expensive, but they were not that easy to find locally. And, compared to the cost of new cast iron radiators, they were cheap. The two used ones cost something like $100 and $75 dollars each (one was for a very small bedroom and the other for a small bathroom -- so neither was very large). But, new cast iron radiators the same size would have cost a few hundred dollars each, at least.. All of this is just for the replacement radiators themselves, not labor. I bought the two used cast iron radiators from a local, old-time, plumbing supply place in an old inner-city neighborhood where they get them from old home tear-downs. They pressure-check them and, if they are not cracked they sell them for re-use. If they are cracked, they sell them to a scrap metal dealer.
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I can understand the problem caused by the rapid heat loss of finned baseboard compared to CI radiators, but wouldn't this be minimized by the fact the circulator runs 100% of the time? Wouldn't the continuous circulation of hot water keep the finned baseboards at the same temperature the CI radiators are regardless of whether the boiler was heating or not?
And wouldn't CI baseboard units minimize this even more? My ground floor is four large rooms, all mostly very open to each other with lots of air circulation. There are 7 CI radiators spread throughout these rooms and I want to replace two of them with something less obtrusive, like baseboard. This is one zone, with constant water circulation, and it's hard for me to see why CI baseboard would be such a problem.
Thanks, Tom

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The Hydronics Institute highly recommends running the circulator all heating season 24/7. They used to be IBR and are now part of GAMA. A circulator for a closed loop heating system should draw less than 100 wats and give you the best heat. Try a Grundfos or Taco cartridge circulator.
Stretch
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Sure and with forced air you can run your blower 24x7. Ive lived with HW for years and run an aquastat. I dought a 100w pump will do it mine is apx 225 watt. it all adds up, for me running 225watts 24x7 adds apx 30$ a month. If you want to do it then be sure to correctly find out the btu of what you have, it will take research, don`t guess. Then oversize the baseboard and use valves to throttle it down if it is to hot . Another consideration is boiler temp, although you say you are set at 170 my boiler never reaches 170 till apx 0f outside. Otherwise 140-155 is all it reaches. Some Baseboards are designed for 170-190 you need to know btu output at low temps, Large cast iron start putting out heat at apx 85f. Im guessing but Id look into also water capacity and mass in Lbs. of both to help in matching. I would be sure if I were doing it to oversize output and have a valve you can cut back water to only that room , non others on that run-takeoff. If you research it well and can cut that room down it will work. " The Wal l" is a good group you will get alot of boiler pros at, and answers, unlike alt. Hvac "hacks"
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thermostat, then, circulators could run 24/7 as the boiler water temperature is maintained relative to the outside temp. Bottom line is a comfortable, more stable house temp.
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Circulator pumps are not supposed to run 24x7 unless you want to waste electricity. Will it work, you`ve gottten opinions, so try it and let us know if you are happy.
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My boiler installed highly recommended that the circulator be set up to run 24x7. I've tried it both ways, and there is definately an improvment in the evenness of the heat throughout the house when the circulator is run all the time. The electrictal cost is small. r

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