Cast-iron & fin-tube baseboards on the same system

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Old 01-09-12, 04:41 PM
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Cast-iron & fin-tube baseboards on the same system

Yeah, I know - it's not recommended because of the different thermal characteristics. The cast-iron baseboards will heat up and store a lot of heat, while the fin-tube units won't store any appreciable heat. But I have one room with fin-tube, and the rest of the house is cast-iron. It's a monoflo system, all on a single zone, but with four separate physical piping loops.

How can I most easily improve the performance of the room with the fin-tube units? One way, of course, would be to ripout the fin-tubes and replace with cast-iron (a lot of work, before I'd do that, I'd probably just live with the situation). Here are some other thoughts I've had:

Add a pumped zone for the loop serving the room in question, but there are two other rooms on the same loop. Maybe add a zone valve for the other two rooms, cutting off their supplies when there is a call for heat from the room in question but not a call for heat for the whole system? Complicated.

Thoughts?

Add an electric baseboard for the room? Higher "fuel" cost.
 
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Old 01-09-12, 05:12 PM
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Thinking outside the box...

Some way to increase the thermal mass of just that room...

How about a buffer tank on just that room's piping... set up in such a way that you will have definite gravity flow from the tank to the emitters, even AFTER the pump shuts off.

So, ya get a heat call, the flow goes through everything as normal, and in doing so recharges the small buffer tank. When call ends, the fin-tube will act more like cast iron... gravity flowing heat out of the buffer...

What ya think?
 
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Old 01-09-12, 05:19 PM
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That's a very interesting idea. The room is on the first floor, and I'd put the tank in the basement, with an aquastat and a small pump to feed one of the two fin-tube units. Or maybe natural circulation would provide the flow without a pump?

As it happens, I have an old cast-iron radiator, not too large. That might be used as as the buffer tank - insulated and located in the basement.
 
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Old 01-09-12, 05:23 PM
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I would try to get it to gravity flow... eliminate the pump...
 
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Old 01-09-12, 05:23 PM
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I'm not sure the cast iron rad is going to have enough water to be your buffer. Especially since it is designed to give off its heat quickly. So I think you will just lose the heat to the basement. Why not put that rad in the offending room?

Do you have indirect hot water? You can pipe that room off the indirect. That way you won't short cycle the boiler with a micro zone.
 
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Old 01-09-12, 05:25 PM
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Our post crossed. - natural circ? And insulate the buffer radiator in the basement? Forget about the water in the ci radiator - think about the c.i. itself.
 
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Old 01-09-12, 05:26 PM
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Heck, just bolt that rad to the floor joists under the room and insulate all around! uh-oh, that sounds like radiant!

Sounds crazy, but I've actually seen it done... and it wasn't a NEW installation, it were OLD! And this was a HUGE rad... bolted horizontally to the joists below the living room, and piped into a big ole coal boiler. I think it was actually used as a 'dump zone' in case the boiler overheated, but I bet it made that floor nice and toasty!
 
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Old 01-09-12, 05:37 PM
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Wow! Sounds like one person needed to really shut another's person yap about her cold feet!

Like I said about the cast iron rad. It's designed to give off its heat. A buffer tank isn't.
 
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Old 01-09-12, 05:46 PM
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The rad would hold it's heat if insulated... but that does lead to another issue with a rad... just as it takes it's sweet-a55 time giving up it's heat, remember that it does the same taking in the heat. So in the time that the boiler runs on a typical heat call, you might not be able to fully recharge it.

I dunno... something to experiment with.
 
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Old 01-10-12, 08:21 PM
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Umm, how about reduce the flow in the cast iron portion? Use thermostatic radiator valves?

Yes, I know monoflow systems need a certain amount of flow to work right going past the venturis. But if you let the mono loops automatically throttle to avoid overheating, the end effect would be like a zone valve. The fin-tube "zone" would then be more like a constant circulation zone. It would also see increased flow rate as the cast iron loops throttled, so you'd get a tad more output.

Where is the thermostat with respect to the cast and fin-tube? I'm assuming not in the area served by the fin-tube, thus underheats or has greater swing.
 
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Old 01-11-12, 10:10 AM
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You can get the thermostatic radiator valves which allow radiator bypass so the flow through the venturi is always correct.
 
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Old 01-11-12, 03:38 PM
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I looked for some 3-ways last year and couldn't really find anything... can you point us to a manufacturer that sells in the USA ?
 
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