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?
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.
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.
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.
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
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
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.
It's very common practice to use
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.
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.
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.
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 $75 dollars each (one was for a very small bedroom and the other for a
small bathroom -- so neither was very large). But, new cast iron radiators
the same size would have cost a few hundred dollars each, at least.. All of
this is just for the replacement radiators themselves, not labor. I bought
the two used cast iron radiators from a local, old-time, plumbing supply
place in an old inner-city neighborhood where they get them from old home
tear-downs. They pressure-check them and, if they are not cracked they sell
them for re-use. If they are cracked, they sell them to a scrap metal
I can understand the problem caused by the rapid heat loss of finned
baseboard compared to CI radiators, but wouldn't this be minimized by the
fact the circulator runs 100% of the time? Wouldn't the continuous
circulation of hot water keep the finned baseboards at the same temperature
the CI radiators are regardless of whether the boiler was heating or not?
And wouldn't CI baseboard units minimize this even more? My ground floor is
four large rooms, all mostly very open to each other with lots of air
circulation. There are 7 CI radiators spread throughout these rooms and I
want to replace two of them with something less obtrusive, like baseboard.
This is one zone, with constant water circulation, and it's hard for me to
see why CI baseboard would be such a problem.
The Hydronics Institute highly recommends running the circulator all
heating season 24/7. They used to be IBR and are now part of GAMA. A
circulator for a closed loop heating system should draw less than 100
wats and give you the best heat. Try a Grundfos or Taco cartridge
Sure and with forced air you can run your blower 24x7. Ive lived with HW
for years and run an aquastat. I dought a 100w pump will do it mine is
apx 225 watt. it all adds up, for me running 225watts 24x7 adds apx 30$
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"
If you get one of those computer controlled boilers without a wall
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.
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.
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