I have a hot water heating system that uses cast iron radiators in each room in the house. I’d like to remove the radiator in the dining room and replace the window it sits below with a set of in swing french doors. Of course, I still need to heat the room, but don’t want to put radiators on either side of the doors as that defeats the purpose of having the doors be in-swing doors. I was thinking that I would put the radiator in the floor with a grill over it. Regio radiator makes a product which is basically a six foot long piece of copper fin tube in a steel box with a nice grill on top. I’m concerned however that putting a fin tube radiator in a system that otherwise has all cast iron radiators is a bad idea as the fin tube relies on a continuous flow of water, whereas the cast iron radiators heat up and then radiate for a while without the hot water flow. I would think this would leave me with a dining room that is much colder than the other rooms in the house. Am I wrong? Is there some other approach I should be taking?
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I'm going to think out loud a bit. For a hydronic system, ideally, the pump will ALWAYS be on in the heating season ... adding JUST enough heat to offset the load. That means a hot water temp that is set 'perfectly'. Understanding that perfect isn't really possible, but knowing what perfect is supposed to be helps understand what you should do. I think the fin tube in the floor idea is fine. You need to have an air 'return' for it. I'm less sure about the science of the incompatibility w/ cast iron. Again, ideally it may not matter if you have the water temp adjusted right. Isn't there such a thing as a 'slim' cast iron radiator that provides the function you talk about? Seems like maybe I've seen them ... but I have a bit of CRS.
I'd never heard that the circulator was always supposed to on and, in fact, my system is not set that way. The way the system works is as follows. (It's single zone, by the way.) The thermostat is in the front hall and is set for 65 degrees during the day and 55 degrees at night. For the first call for heat in the morning, the cirulator starts running. The water temp in the furnace drops soon thereafter and the burner kicks in. Eventually the radiators heat up, the air temperature rises to 65 and the circulator kicks off followed by the burner. I just checked the furnace, the cirulator is not running and the water temp is 160 degrees. The system is also used for domestic hot water. Does this make a difference?
It's really a fairly simple calc. First, figure out what temp your system is set at. Then, look up your fintube and you should be able tell how many BTU's/ hour per lineal foot. There are also sites out there that will tell you how many BTU's a CI radiator of a given size/water temp puts out. I'm going to predict that at the temps that cast iron radiators run at, you're not going to get near enough heat out of fin tube.
Here is a link to the recessed fin tube radiator:
http://www.reggioregister.com/prod_detail_list/34The register I am replacing is 16 sections that have 5 tubes. Their height is 25". Bear in mind, however, that the system was installed in 1929 when there was no insulation in the walls and the windows were single pane. I have slowly insulated the house and have replaced all the other windows with double paned, argon filled windows.
I couldn't find the water temperature on there, and I really don't have the energy tonight to dig too much (H1N1 has struck). I am partly basing my response on the fact that I added a few fin tubes on my system (mostly CI) and it didn't work for s***. I thought it would because the mudroom they were in is very well insulated,but that wasn't enough.When you think about it, it's kind of doomed to failure. A cast iron radiator is like a big pot of hot water. Turn your thermostat up, wait for the radiators to get hot, then turn it off. Your radiators will stay warm for a long time. Think of the water in a copper fin tube. After the boiler shuts down,it's going to get cold in a hurry.Other posters have talked about systems using continous pumps. I believe that involves a thermostatic mixing valve with an outdoor reset controller. That means that the system temp is adjusted according to the temperature outside. This is over my head to comment on. I tend to think it would not solve your problem. I would look for professional help before going too far. Supply houses usually have a heating designer, and I think system design might even be available on the internet.
Your rad is good for about 8160 BTU's /hour at 180f water temp.
The largest grille is 6000.
Your call.
And what do you get out of your cast iron rads if you run 180 degree water into them?
Oh wait, you're already talking CI. I came up with 9520 but I suppose that's splittin hairs. Flow rate will probably mess up these numbers, being that your system will shut down when the call for heat is satisfied by the cast iron. I suppose you could throttle the cast iron way down to compensate. I think it's safe to say that there is probably more to it than just plugging in the new floor box.
A room that warms up very quickly?! Is this a trick question? If you thermally shock them, it may be different (and a detail I'm not privy to).
If a circulator pump is always running something is wrong. The dining room will get colder quicker and stay colder longer than the other rooms. Radiator types should not be mixed within a single zone.
I disagree. If you think about it ... having the continuous run provides maximum efficiency and comfort. The system (or you) reset the water temp based on the load, the circulator will always run ... again, in theory. That is because you've set the supply water temp to exactly match the heat load ... and the stat would always be just at the setpoint, maybe a hair low. That way, you don't turn the system on/off and have the fluctuations in temperatures ... nice and steady wins the race so to speak. Most efficient and most comfortable.
The extreme is to have high temp hot water and the system comes on full bore ... then shuts off. Meanwhile space temp swings up and down as the system goes on/off. The concept above is the same used in commercial applications where automatic controls reset the supply water temp based on the load (either the outside air temp or the zone needing the most heat).
Do you have reasons why radiator types shouldn't be mixed? I'm not disagreeing, because I really don't know, but others reading this don't usually take statements at face value and often want to know the why behind the statements ... to learn something.
Constant Circulation with outdoor and indoor reset is the best option. Also requires more controls.
Mixing different types of heat emitters is generally not a great thing to do. To get the required output, they require different water temps or the size of heat emitter has to be adjusted.
I used the poor mans reset ... a manually adjustable 3-way valve ... and then adjust it occasionally during the season. Early season is a cooler water temp than later on. It seems to work fine. I think I priced automatic controls and one guy gave me a price of like $800 ... so I opted for the manual adjustment. Seems like automatic controls should be cheaper. Maybe I should have went pneumatic. :) If you knew what you were doing, you could probably scavenge some commercial controls and make them work ... but I know little about those computin' machines 'cept how to log onto Breaktime.
pnuematics is LOTS more money.
Also a dying art/trade craft.
My opinion comes from my father who has done alot of plumbing in his 70 years and from a plumber friend of the family who all say not to mix radiators types on a single zone. A ci rad will stay hotter longer than a fin type. Rooms with ci will be warmer longer than a room with fins=colder room. If the thermostat is in the room with the fins it will turn on the system before the other rooms reach the lower temp of the fin room=one warm room,lots of hot rooms.
As for a continual running pump, i don't get the concept.Controls for that would be new to me. It might work for fins but i do not see it working on ci rads. They continue to give off heat once warmed up. Example my house is 68degrees, iturn thermostat to 70. Pump comes on, furnace fire up, when room reaches 70 it shuts off, but my house will heat up and continue to heat up after pump shuts off.
Continuous running pump is most ideal for e.g. concrete radiant floors which have even more mass than radiators. But if the water temp matches the load properly, you won't have the problem that you refer to. In fact hot water reset (which is what it is called in the industry) is designed exactly to resolve that problem ... particularly in systems that have e.g. hydronic concrete floors.
Once the floor heats up to the general temp you want it to be at, rather than bring the system on and heat the space up and then shut them off, you 'simply' provide just enough water temp to just reach (or just shy of) the set point. This way you continuously provide just enough Btus to satisfy the heat loss ... no more ... no less. This avoids the temperature swings that you refer to. This concept has been used for decades in commercial applications.
In my radiant system, I have adjustable 3-way valves. I set them at a low temp during the early winter and gradually increase their setting when it routinely is colder out. Not automatic reset, but its a reasonable approach.
I think if you reset the water temp, you might get away with mixing radiator types. But maybe there is another reason you wouldn't do it, too.
Edited 10/19/2009 8:17 am ET by Clewless1
I sorta get it but like i said it is new to me. My question is what is the heat source? Electric, or gas. I Burn coal and can't see it running constantly, there would be alot of waste and it wouldn't burn efficiently.
One advantage of a coal furnace or boiler is the water in the water jacket is always warm so when the pump kicks on it is instant warm water circulating, there is no waiting like with gas or oil. I am not familiar with all types of boilers, so maybe some run to keep a constant temp of water in the coil or jacket. Coal burners always have heat source though. No fuel like an old fuel.
I'm not talking about the boiler running constantly; it's the circulating pump (that is controlled by the thermostat). The boiler runs as it needs to to maintain the boiler temp. On cold nights the temp drops more/quickly and triggers the boiler to run more. The stat causes (or not) the pump to use more of that heat (or not).
I am not getting your notion of coal vs. oil/gas. They are essentially all the same, given the same boiler characteristics (i.e. type, size, HX configuration, etc.). The water 'in the jacket' is always warm ... maintained by the boiler setpoint/stat that is determined by you ... set it at e.g. 180 or set it at e.g. 130 ... depending on your needs and the system design. When a pump kicks on a call for heat, it draws the warm water out of the boiler to do so ... regardless of fuel type.
Constant circulation with TRV's on CI rads and a outdoor set back is the best for control from room to room comfort.
Without seeing the rad, it's hard to say if 6' will be enough.
Describe your rad. How tall? How wide? How many "tubes" in each section? and how many sections?
Got a link to the fintube?
I've never seen that to be successful. Your suspicions are right, the room will be under-heated. You need to match the mass of that radiator with something comparable. Another problem is that fin-types operate at higher temperatures.