Adding Steel Panel Radiators

Bridgestone

Our house has a gas boiler and three zones with three thermostats. Two zones have cast iron radiators. Zone 3 is a house addition using 3/4 inch copper-fin baseboards for heat. It's on a single loop with additional copper-fin running in basement joists under the floor. The zone is small and short-cycles at 180* because the baseboard heat is not satisfying the thermostat. I plan to remove two or three baseboard heaters and install two or three steel panel radiators on a 1-pipe system using Caleffi bypass valves.

If I keep one baseboard heater in the loop can it be located between two steel panel radiators? Will the bypass valves have any meaningful impact on water flow back to the boiler? Is Pex tubing safe to use if there is still short-cycling at 180*?

EdTheHeaterMan

If you are talking about the Caleffi 519 series valves, there is a specific reason for that device. A one pipe system you are mentioning may not be the proper use.

To be clear a One Pipe design would mean that the supply and the return of each radiator is connected to the same (One) pipe as illustrated here

This system requires diverter tees and must be properly designed to have a balanced system.

I believe that you actually mean a series loop system not a one pipe system. Normal baseboard convectors with finned tubes use this series loop regularly like this illustration



If you try to put two different heat emitters on the same series loop, you will be disappointed in the results.


Your best use of panel radiators to increase the heat needed in the troubled area is to have home runs to the boiler room or at minimum a direct return type system where the radiator supplies are connected the the boiler supply and the radiator returns connected to the boiler return with a circulator somewhere within the circuit feeding those radiators.


Those radiators can operate from the same thermostat, zone valve or circulator that is operating the existing zone. Some logical designing and piping will be needed to accomplish your goal.

Bridgestone

Thanks Ed. I plan to use 3 Celeffi 3012 bypass valves which have a diverter function within, 35% to the radiator loop and 65% staying in the supply line to the next radiator. The valves are adjustable. I will not leave a baseboard heater between the 3 new steel panel radiators. After the last radiator the return flow will go through copper finn running under the additon floor, in the joist space, and then to the boiler. Becase the zone is small and I have a 109,000 Btu boiler I think I will get heat beyond the last radiator. Does that make sense? The house has a larger main zone, but at times we only want to run the smaller zone, thus some short-cycling.

Big Ed_4

I would recommend to change out the baseboard and replace it with panels ..

kcopp

Another simpler solution would be to replace the baseboard w/ baseboard that has a higher output...
Petite 9, Sterling Senior or Heating edge 3

Bridgestone

Still have a question. Given a 3/4" main pipe will diverter tees or diverter valves provide the same flow rate through the system. I'm wondering about the flow rate beyond the last radiator that enters 3/4" copper finn under the floor and back to the boiler. If diverter tees are used, are they put on the supply or retrn side of the radiator piping. Still concerned about short-cycling. Thanks much for your input.

EdTheHeaterMan

Bridgestone said:

Thanks Ed. I plan to use 3 Celeffi 3012 bypass valves which have a diverter function within, 35% to the radiator loop and 65% staying in the supply line to the next radiator. The valves are adjustable. I will not leave a baseboard heater between the 3 new steel panel radiators. After the last radiator the return flow will go through copper finn running under the additon floor, in the joist space, and then to the boiler. Becase the zone is small and I have a 109,000 Btu boiler I think I will get heat beyond the last radiator. Does that make sense? The house has a larger main zone, but at times we only want to run the smaller zone, thus some short-cycling.

Looking at the Caleffi valve you mentioned, and the fact that you have less than 40,000 total BTU output of radiation with the baseboard and panel radiators, either of these two diagrams should work.

Preferred.

Acceptable:

as long as you feed the valves with 3/4".
If you reduce to 1/2" in any section of the series loop, you will cut down your total zone output to the amount of heat that 1/2" tubing can handle, about 15.000 BTU

Big Ed_4

I like the "better design"....

Bridgestone

Ed, you stated that (as long as you feed the valves with 3/4"). From the videos I watched it appeared that the Celeffi 3012 diverter valves had a 1/2 " feed. Was that compressed down from 3/4"?. Can the valves have a 3/4 " feed?

EdTheHeaterMan

In order to be as clear as possible on this point, I recommend that you read the first few pages of this book. (pages 4, 5, and 6). Read than more than once. https://s3.amazonaws.com/s3.supplyhouse.com/product_files/108119-Reference Guide.pdf
There are simple designing rules that must be followed to ensure that you get the heat from the source to the radiators. If the pipes are too small then you will not get all the heat from the boiler to the radiators. Here are two of those rules:



If the valves you wish to use are only available in ½” then your piping any portion of the series loop will determine the maximum amount of heat that the rest of the pipes on that loop can move from the boiler to the radiators. In this example, the design will restrict the maximum flow rate to 1½ GPM.


As long as the total heat needed for that zone is 15,000 BTUh or less, this design will work. If you actually need more that 15,000 BTUh to properly heat this zone, then you will need to select an alternative design or get 3/4" valves for those radiators.

If 3/4" valves are not available, Then you should consider this piping design.

EdTheHeaterMan

A closer look at the Caleffi 3012 valve indicates it will accept a 5/8" PEX tubing connection. There is also a 3/4" PEX-AL-PEX fitting that will fit that valve. You should be fine using that valve, Just get the tubing size that will provide the needed flow rate for the entire loop. Then adjust the bypass to allow the needed GPM to continue to the next radiator or back to the boiler.

Bridgestone

I read the pages you referenced, thanks.

I've decided to install a 3/4" manifold and do home run connections to 3 steel panel radiators in a large room, using 1/2 " pex. All runs would be less than 15'. I would like to keep 36' of 3/4" bare copper finn running in joist patterns under the floor to a different room. That run has 1 3/4" square finns, smaller than standard, so not sure about btu output.

I could feed the copper-finn run with 1/2" pex from the manifold, or feed it directly from the boiler and then to the manifold for home run connections to the radiators. Is one method appreciable better than the other? Radiaor perfomance is the top priority. This would be the entire heating on this zone with a thermostat in the room with the radiators.

Jamie Hall

Um... er... there is some fundamental thermodynamics which seems to have gotten overlooked here.

The output of a given amount of baseboard, or a given radiator, operating on hot water, as is the case in this system, is very closely proportional to the average temperature of the water in the unit minus a constant (conveniently taken as 80). It is related to the flow through the unit only indirectly.

An example. Let's suppose we have a 10 foot baseboard rated at 580 BTUh per foot at a water temperature of 180 F. Now if the average temperature of the water flowing through the unit is in fact 180, that baseboard will deliver 5800 BTUh. It will also extract that 5800 BTUh from the water flowing through it. Now let's further suppose that that unit is supplied with 1.5 gallons per minute of water. Call it 12 pounds per minute, to keep this on the back of an envelope. That's approximately 720 pounds per hour. Now extracting the 5800 BTUh from 720 pounds per hour of water the temperature must drop -- in fact, by about 8 degrees. Now recall that we said that the average temperature is what counts, so if we lose 8 degrees going through that radiator, the input must have been 184 and the output must have been 176/

So far so good?

Now if our baseboards are in series, the next one doesn't get 184 degree water, it gets 176 degree water, so it's output will be less. The math can get messy if we mix units, so let's just consider your 40 feet of baseboard in series. If the average temperature of the water across those 40 feet really was 180, you could expect to get 20,000 BTUh out of them A little higher than the rules of thumb above, but not outrageously so. But -- what must the input temperature be to do that? Well, the thermodynamics says that the temperature drop with that flow to provide that amount of heat is 32 degrees. Problem. Out input water isn't at 196, it's at 180 -- so the output temperature will be around 148 and the average won't be 180, it will be 164. Remember that the output is more or less proportional to the average water temperature minus about 80 -- so the actual output will be more like 17,000 BTUh (oh ho -- so that's how we get 15,000 BTUh from the rule of thumb. Round numbers!).

But in the diagram we have some radiators now at the output of those baseboards. They're not getting 180 degree water, they're getting -- as the input -- only 150 degree water. Their output will only be about 60% of what they are rated for, because of the lower water temperature.

All of which is sort of the long way of saying that if you are running a series loop, you can't calculate the output of a given unit based only on the flow. You have to take into account the drop in temperature of the water as it goes through the loop.

You really can't compensate for that with higher flow rates, as the velocities will get too high in the pipes.

Pipe your system in parallel, not series, and you will be much much better off. That way all your units get the input water temperature, rather than a tepid bath.

Bridgestone

Br. Jamie - regarding my question, if I understand correctly I should run seperate 1/2" pex from the 3/4" manifold to and from each of the 3 panel radiators using isolation valves. That would be parallel piping for those radiators. Also, from the manifold I should connect 1/2 pex to the copper fin loop in the joist pattern under the floor of an ajacent room. The last emitter of that loop would not perform as well as the first emitter because they are connected in series. I'm most concerned about performance of the radiators in the room with the thermostat and will take what Btu's I can get from the copper-finn loop under a floor. Or I suppose I could split that loop and have parrellel piping to each loop from the manifold, but not to each emitter. Am I understanding this correctly? Thanks for your input.

Jamie Hall

You've got the principle -- keep working on it!

hot_rod

A few other options with either electric actuators, better yet TRVs for individual control.
A delta P circulator help determine flow rate based on zones opening and closing.

The tubes inside some panel rads would be the flow restriction to a series loop.
Looks like about a 12mm OD tube in these Dianorms.

More info in Idronics 23 about adding heat emitters.

Bridgestone

Hot Rod, thank you for the very clear picture. My boiler has an air vent servicing all three zones, should the manifold I select also have an air vent. The other 2 zones in the house are higher.

As an aside, the prior owner, due to a house addition, placed 210 feet of copper pipe containing 102 feet of copper finn on one series loop. The 15' of 3/4 baseboard in the valulted ceiling room will not satisfy a 66* thermostat on cold days, and the boiler shortcycles, 180 to 160 and back to 180, frequently. So I have limited heat and aggravating shortcycling. I've been getting along on clold days with a space heater to satisfy the thermostat setting. Any improvement will by enjoyed.