how to pipe a radiator

John Koll_3

We have disagreement among us about how to pipe a cast iron radiator in a conventional hydrnoic heating system... supply in the bottom and return out the opposite bottom or opposite top... or supply in the top and return out the opposite bottom.  We haven't found anything illustrative online or on The Wall.  Anyone have any depcitions of the recommended connection, please?

Gordan

Bottom to bottom is best.

Buoyancy will make sure that hottest water makes it to the top.

Big Ed_4

Hot Water Radiators

Either pipe a radiator supply bottom - return bottom or supply top - return bottom ...



If the supply and return , both are piped to the top ....Water would only flow through the top section , thus just the top part of the radiator would be warm ....



If you supply the bottom and return from the top , you just made a heat trap which would restrict the flow...



If the supply is on top and the return is on the bottom , on the same side of the radiator , only the first section would warm up...



You can supply through the same bottom using a double tap bushing , just need to extend one of the tap with a internal pipe to the other side of the radiator ... Or top feed bottom return with a single bushing extending an internal pipe across the inside of the radiator... Supply or return but just one ..



Which is better , top-bottom or bottom-bottom ? With Top-bottom the radiator will fill more evenly across , it would be like a reverse return . All the passages through the radiator would have equal distance. Panel radiators are piped top supply -bottom return..



With bottom -bottom the warmth would work its way across each sections , as each section fills with near equal supply temperature ...



... With cast iron radiators piped bottom-bottom, you don't have the sometimes unsightly top supply pipe , unless you pipe it in polished brass which I think looks cool ...

Charlie from wmass

ED I have an old radiator

I tried to save from an old gravity system. The supply and return are both on the same side at the bottom. The existing ones that did not get cracked actually heat quit well. I will need to get photos of the cracked one I have with the side by side 1" tappings.

Big Ed_4

Gravity

I could see a double tap with out the internal pipe work on a gravity , not sure with the restricted tapings.( Size matters on a gravity) or how it worked in its heyday when the windows where open ... I am sure its not the best way ..I am thinking someone cut corners even back then ..

jublack2000

bottom to bottom piping question

Hi there,



I have some old rads where the piping for supply and return are at the bottom on the same side. I also have some where the supply and return are at the bottom on opposite sides.



Does it matter which one is used as the supply and which one is used as the return?



If so, how do I tell the difference between the two?



Thanks for your help!



Juliana

J_Lin

radiator hot water piping

Our renovation/restoration is a 1920 American foursquare containing a number of first and second floor CI rads - I have been reading this thread to acquire knowledge regarding the piping of these radiators once the system has been updated to include circulators.  The existing gravity system incorporated piping into the radiators at the bottom on the same side of the radiator.  The hot inlet was valved by a device that allowed a 1\4 turn.  The valves are no longer usable because of deterioration.  I have read through "Classic Hydronics" and have gained an understanding of how radiators may be short circuited with conventional piping due to the nature of increased flow from the circulator.  I know you know what I am going to ask.  Is this original piping going to cause a problem inside these radiators?  May I introduce the hot water at the top opposite corner of the radiator? 



The original gravity system piping has been removed due to age and corrosion.  It was a good system and I can vouch for that as I grew up in this old house.  I have replaced these lines using Wirsbro 1" for the direct return and teed off 3/4" for the radiator runs.  I will be using 3/4" iron stub pipes through the main floor from the first floor radiators for aesthetic reasons and connecting to the PEX under the floor.  The second floor radiators will be plumbed in exposed 3/4" iron down through the first floor and connected again under the first floor to the PEX. 



It is my understanding though, that I will need to re-plumb the radiators to supply hot water at the top corner and return water at the opposite bottom corner in order for these radiators to work properly.  I would very much like to use the TRV for temperature control in the rooms.  I am at the beginning of this project and welcome your insight and thank you in advance for reading this. 

J_Lin

Well after much work plumbing pipe, restoring radiator fitting threads, running HePex and purchasing a variety of tools including the milwaukee ProPex enpander I was up and running three weeks before the cold snap hit. 9 rads are plumbed in leaving two to go once those rooms are finished.

Trinity Tx Combi - no DHW tank - all is well this winter

NO2nice

J_Lin - how did your project go? I am doing the same thing and was going to pipe my radiators Bottom-Bottom. I have nipples on all 4 corners of the radiator so i can technically do any configuration.
How did you size your circulator for this project?

icesailor

IMO & Experience, bottom to bottom is the best all around way. Any time you pipe radiators diagonally, you run a risk of the water UNDER the diagonal. not being hot, or as hot. Even if you feed one side at the top and return at the bottom. Especially when over pumped. If you feed one side, always feed the hot entering at the top. If you feed at the bottom, the hot can run right up the first few sections and out the top. Especially if over pumped.

wmtandson

jlin we need pictures
thanks

J_Lin

Thanks for the interest. Circulator is a Taco 007 F5 - sufficient for 11 rads I'm told but I can go bigger if needed. This circulator runs 24/7. I have 9 rads tied in now, all set with Danfoss trvs, and am running a differential bypass valve which returns after the boiler to keep return temps as low as possible. It is -28C tonight here and things are humming along nicely. The boiler has not yet run into high exhaust temps and continues to condense even in this bitter cold. Interesting subject is the radiator piping. I chose to supply at the top and return opposite bottom, with the thought that if i had problems then I could change all that in the heating off season. The arrangement is very interesting.

I haven't had any problems with cold rads period. Once the trvs were fitted I found the return temps lowered. The rads closer to boiler supply were throttled and the rads further down the supply were heating properly. The interesting result I noticed after the trv began throttling was that hot water remained in the opposite diagonal and shed its heat over a good period of time. No cold rads, and no cold sections of rads. This does work. I should note that although the rads are piped 3/4" the orifice in the trv reduces that to just over a pencil size. The water movement through the rad is quite slow. I was worried about this, however by asking the right questions I was convinced all would be well. Surprisingly, the rads heat very quickly, and the hot water does hang around a long time.

Now, the exposed piping may not be aesthetic and that would be a personal decision. It suits this 1920 two storey though, as the first to second floor piping is also exposed. I did come across an excellent article on heating help that directed me in this process and will have to find the link some time later. It is worth reading.

The HePex is a god send in my opinion, and the ProPex system of connecting could not be easier. The system is a two pipe direct return through a primary header, and if needed I could easily make this a reverse return. I definitely have enough left over material. The only reason I would consider this is to see what would happen to the return temps. I chose direct return because of the CI baseboard I will be adding to heat the house entrance.

I cannot send any photos at this time as i do not know how to post them, but once i figure that out I may add them. Its not much to see tho, just some old rads in a nice old home.

J_Lin

Hi again - as requested by wmtandson I have a few pictures to upload - The rad piping is painted as of yet but all things take time - The Danfoss TRV is on the supply end of things. The piping is designed to be tucked away so that normal living won't bump into things. The rads have been finished in black and I believe it helps the radiation. As one enters a room the radiator can be physically felt from across the room. I have listened to similar comments from visitors.

The final photo shows the work being done on the final room to be restored (present work in progress). This room was the original master bedroom. The radiator shown is comprised of 18 sections as opposed to the guest rooms having 13 sections. It is a heavy rad and easily much too large in this day and age for the room requirements. However it will be cleaned up, painted and piped in. It is much too large to remove.

This is our fifth year of renovation and restoration work on this house. It has been a great privilege to be able to progress to this point.

Charlie from wmass

Bottom to bottom for full rated output. Others have posted infrared images to prove this.

icesailor

Charlie from wmass said:

Bottom to bottom for full rated output. Others have posted infrared images to prove this.

That may be true, but with TRV's, is it better to control the temperature on the floor or higher up in the room? Where that TRV is located?

I'll take the higher up for comfort.

Paul48

In that case, get a TRV with a remote sensor, and put it where ever you like.

icesailor

Paul48 said:

In that case, get a TRV with a remote sensor, and put it where ever you like.

That's always a possibility. But my experience with the nuances of some people seeing some unexpected object on the wall that appears to look like a phallic object with a wire running out of it , connected to some object on a radiator.

You never know what will ignite someone's senses.

Charlie from wmass

Dial and sensor on wall together.

Henry

here is the prefered method from Audel's Engineers and Mechanic Guide of 1921

vaporvac

Holy moley, Henry. That book is AWESOME! I love the web and free books.

bob_46

thats for an overhead gravity system

Charlie from wmass

1953 Starbuck's Modern Heating Illustrated

J_Lin

The trvs are doing their job and its nice to have them located out of the kicking zone. Bottom to bottom piping would be ideal to encompass the rad volume directly under what is the top supply piping. I chose this piping because I wanted the trv up higher and I suspected the flow restriction of the trv would facilitate even heating of the rad. Temperatures fell low enough this year for an adequate evaluation of the heating system, although not into the historically -40 lows. I'm happy with the operation but I also realize how the bottom to bottom piping would increase efficiency.

J_Lin

BTW all of this wouldn't have been possible without this forum. Thank you for the information and help. I'm pretty good at working with metal but useless without procedure.

J_Lin

Hi y'all -btw Dan's book (What Hydronics Taught Holohan) is wonderfully written and answers many questions about life in this industry. Thank you Dan for putting this book together. It isn't easy, I realize, to edit a lifetime into a book. I realize your other publications I have in my possession complement this volume. As individuals express interest in our renovation the most interesting questions are directed at the CI rads and how the uniform heating was accomplished. I always explain I had excellent help and if anyone cares to find out I have the books.

As an update on this old gal of a home, the last two of the second floor rads were piped in November 2015, at which time I did convert the system to reverse return. I had concerns of the direct return failing to fully heat the last rads on the loop while coinciding with boiler return temps higher than those particular rads.

It isn't a particularly difficult change as I had designed this transition into the loop, thinking ahead as I was taught (thanks again dan) in the event the direct return may not perform as desired based on this house configuration. I am happy to say all is well with reverse return. Eleven rads, two stories, 1800 sq.ft combined, all supplied by one circulator, and the most comfortable home I have lived in with the quietest heating system.

Regarding the top fed CI rad. Although it has been explained that bottom bottom piping results in better CI rad efficiency I can, at this point after two long winters, say confidently that it works sufficiently without problems. I prefer the TRV at the rad top personally and I really like the danfoss simplicity.

Thank you for the help over these past years, figuring out how to get this all to work.