cast iron rads stealing my BTUs ;-)

Phil_6

I have a couple of jobs where there is some big old house with a big old converted gravity system and a couple of little zones of baseboard off to the side. I find that the return water from the main zone dumping back to the boiler will be so cool for so long that the water heading out of the boiler will never reach a high enough temp for long enough to really get the baseboard kicking on a real cold day. The main part of the house will be nice and toasty with the water at almost any temp but the other areas just can't keep up.
What are my best options for getting some of those BTUs swimming around in the cast iron over into the baseboard where they are really needed? Besides wanting to protect the boiler if it's the non condensing type. I've boosted the water temp, installed a bypass, cut the differential down on the aquastat as low as it can go and things along those lines but aside from putting in a HUGE boiler like in the olden days, I'm looking for more ideas.The boilers always seem big enough based on heat loss calcs but the heat is in the wrong rooms.

Thanks all, Phil

Mike T., Swampeast MO

You just defined why you don't want to mix fin baseboard and standing iron...

The iron retains heat--it's not "robbing" the BTUs, it has "captured" them and they're no longer "swimming around" when the circulator isn't running...

The iron rads most likely operate at a significantly lower temperature than the fin baseboard. To stay with your analogy, there aren't enough BTUs "swimming around" when the circulator is running to capture in the baseboard...

While I suppose you could set up the system to supply a completely separate, high-temperature zone for the fin baseboard, it would likely be less expensive and more energy efficient to replace the fin b/b with more suitable emitters.

In descending order of preference: iron rads; steel panel rads; iron baseboard.

Thad English

I seem to have the same problem in my kitchen and breakfast room: it's about 5 degrees cooler in there than in other rooms on the first floor. (And yes all of the windows and doors are weather-proofed to the same levels as the rest of the windows and doors on the first floor.) The kitchen and breakfast room have cast iron baseboard and the rest of the first floor has radiators. Would it be worthwhile to change the baseboard out for regular radiators? What other changes to the system would have to be done? It is a 2 pipe air-vent steam system. I will be gutting these 2 rooms next year anyway, so while I'm at it if it will make things more confortable why not do it all at once?

I should be receiving my copy of "The Lost Art of Steam Heat" any day now and can't wait to find the answers to my questions myself, but in the interim: any thoughts?

Phil_6

zones

In every case where I have this problem the fin tube is on seperate zones.It's just that the supply temps leaving the boiler tend to drop down considerably, 150 or less sometimes, when the main zone is running and dumping the cool return water back into the boilers. When it's nice and cold out the baseboard just doesn't get the rooms up to temperature.

Mike T., Swampeast MO

Yea, I see what you mean...

The iron rads can be seeming to "rob" the BTUs. They hold a lot of water and if they cool significantly between runs they'll certainly dump a lot of cold water back into the (likely modern and low water content) boiler...

Are these systems piped primary/secondary and/or does the iron radiation portion have thermostatic bypass to keep its temperature down and the boilers' up?

Steamhead

I solved this once

by running some return water from the main cast-iron zone into the supply for that same zone, right after the zone's flow-check and before the circulator which was Pumping Away. I think the circ was piped into 1-1/4", so I used 1" for the bypass pipe. It worked pretty well, everything got as hot as it should have and stayed that way.

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Steamhead

On steam

the best thing to do is go back to cast-iron radiators or use cast-iron baseboard. Good used ones aren't that expensive and new ones are still made. They come in different shapes and sizes so you're not limited that way. Just make sure they're installed properly- go to the Find a Professional page of this site to locate someone who can do this.

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J.C.A._3

Think about the \"mass\".

I remember a post that Dan made a few months back about the sizzling fajita plate. The cast iron holds the heat for a long time, while aluminum foil can be touched a few seconds after coming out of the oven.

I , to this day STILL don't believe there is a functional way to have these 2 types of emitters on the same zone or circut. Think about the heat being held on both as a graph. The big cast units will look like a "sign wave" from an AC current, while the graph from a strip of baseboard will look like the Sawtooth mountains. Up to temp, thermostat shuts off, and the lack of mass cools way quicker than the bigger, and in my humble opinion, better huge radiators.(A big plus being that Joe homeowner knows he won't be able to put furniture in front of the radiators,vs.having to keep the stuff in the room far enough away so the baseboard could work as designed, thereby making the room SEEM smaller)

My advice would be to zone the baseboard to a seperate circut, or like someone else said, look into some cast iron baseboard. It won't hold the heat as well as a radiator, but will be a closer match to the graph than fintube. Good luck. Chris

Phil_6

Bypass

I have tried the method Steamhead mentions below on a couple of jobs with some success, but I'm trying to come up with something more exact.I see it on a job piped primary/secondary also. By a thermostatic bypass are you talking about something along the lines of a thermostatic mixing valve kind of thing? This sounds like what I'm thinking of. Being able to reliably keep the return water from the main zone, and therefore the supply water, above a certain temp, or at least keep the amount of return water limited. I find these big boy rads heat quite well at almost any temperature since they are so darn oversized, so I'd like to save the really hot water for the fin tube.

Thanks for the help guys,

Phil

Tom M.

This worked for me

I had to replace an old boiler with a Weil McLain GO-5. Two baseboard zones in addition, one 1 1/2" monoflow zone with oversized cast iron rads. I did a heat loss on the area of the house with the cast iron and by one of the charts in Dan's "Golden Rules", it only reqired a 1" pipe at a 20* temperature drop.

I connected the 1 1/2" monoflow zone to itself in a loop with a Taco zoning circulator so that it would maintain the full flowrate that it had before. I then injected the 1" flow with closely spaced tees. I used the relay of the zoning circulator to call the 1" zone valve.

Tom M.

Phil_6

I like it

That's what I like about the wall. So many brains working together. Keeps mine from exploding.

Thanks Tom

Phil_6

I like it

That's what I like about the wall. So many brains working together. Keeps
mine from exploding.

Thanks Tom

jw

an idea

Add more fintube, so that the btu delivered into the room is more in line with the needs of that room. In otherwords, size the fintube to the lower temp water. Should be an easy fix, eh? More fintube or just more convective surface of some sort is the real answer. Does not matter the material, just needs sized for the water temp you are finding it operates at.