Cast Iron Radiators with Wood Boiler

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hedgecutter

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I am helping a guy install a new Outside Wood Boiler in an old school house that has the old cast iron radiators which were originally used with steam. The the old two story school building is being used as a residence and is now being heated with four different propane fired forced air systems. We are planning on installing water to air plenum coils in the two forced are units for heating the first floor, but upstairs we want to use the old cast iron radiators (maybe 1900 vintage) by circulating hot water from the OWB up to a plate exchanger and then plumb two or three different closed loops using pumps and t-stats through the radiators. My question is how to plumb our lines into the cast iron radiators. Some of the rads have inlet/outlets on both the bottom and top on both ends and some on just the bottom. I was figuring the water temp to be around 170 to 180 F.

1. Would you plumb the hot water in the bottom and then out the top on opposite ends? In the bottom on one end then out the bottom on the opposite end? What is your opinion to maximize heat transfer?

2. What about pressure testing and flushing the rads? They have not been in service for decades and I assume there is some crust on the inside.

3. Any other advice or opinions on how to control or plumb this project.

Thanks
 
radiators

As Eric has said you should visit heating help to learn more.


I would not waste any time with forced air heat when you can regulate the heat in every room with the radiator set for hot water!!!!


The radiators should be cleaned by a firm that does this as a part of thier business to be sure everything is ok with the radiators-clean, no sediment
painted for you, tested for leaks etc.

Typically the converted radiator pumps from bottom to bottom through the castings to shed heat.

FYI using the radiators will reduce the amount of dust you have in the home too.


leon
 
Was the steam system a one pipe or a two pipe?

You will definitely need to flush them out before you use them, since there is probably scale and other badness inside.

I think This Old House did a piece on the conversion from steam to hot water, you may be able to find it if you dig around online.
 
This is exactly what I did last year. There is nothing better then the cast iron radiators imho. I converted 18 of them in my house. I had single pipe steam prior. I used some of the origanal inlets and took out the plugs on the bottom of the other side. Put a reducer and hooked pex to that for a return. I was able to go from a single zone to 5 zones. What is nice about the cast iron is it stays hotter longer than the baseboard heaters. Granted, they don't look as nice and they take up more room but they were already here.
 
Also I forgot to sat you have to put a bleeder at the top outlet side. There is a plug there also. Mine had blow offs half way down on the outlet side. Just unscrew those and plug the hole and put the bleeder above that.
 
As Eric has said you should visit heating help to learn more.


I would not waste any time with forced air heat when you can regulate the heat in every room with the radiator set for hot water!!!!


The radiators should be cleaned by a firm that does this as a part of thier business to be sure everything is ok with the radiators-clean, no sediment
painted for you, tested for leaks etc.

Typically the converted radiator pumps from bottom to bottom through the castings to shed heat.

FYI using the radiators will reduce the amount of dust you have in the home too.


leon

Thank you Leon. So pump the water in the bottom on one end and then out the bottom of the other end of the radiator. I was a little reluctant to try and use these old radiators with hot water as I knew they were originally used with steam and I have no experience with radiators. Sounds like a good way to heat.
 
Two Pipe?

Was the steam system a one pipe or a two pipe?

You will definitely need to flush them out before you use them, since there is probably scale and other badness inside.

I think these radiators were two pipe as they have a pipe attached on both ends at the bottom. One is larger which I assume was the steam supply and the other end has a smaller pipe which I assume was the water/condensate return back to the boiler. Does that sound right?
 
You will wanna pipe the supply in the bottom and the return should be out the top on the other side. This will get all the air out of your radiator. A bleeder valve will be a great Idea also to help with air removal when filling the radiator with hot water. Don't pipe both supply and return in the bottom cause your radiator will only have a couple inches of water in it and probable won't put off that much heat.
 
I think these radiators were two pipe as they have a pipe attached on both ends at the bottom. One is larger which I assume was the steam supply and the other end has a smaller pipe which I assume was the water/condensate return back to the boiler. Does that sound right?

Usually in steam radiators the steam will be in the top and condensate will be in the bottom.
 
Sizing

This is exactly what I did last year. There is nothing better then the cast iron radiators imho. I converted 18 of them in my house. I had single pipe steam prior. I used some of the origanal inlets and took out the plugs on the bottom of the other side. Put a reducer and hooked pex to that for a return. I was able to go from a single zone to 5 zones.

Sounds like you are happy with the heat from your rads. So you plumbed yours in the bottom on one end then out the bottom on the opposite end. Do you know if there is any kind of sizing rule of thumb as far as wood boiler water capacity to how much water capacity you can have in your radiators?
 
Sounds like you are happy with the heat from your rads. So you plumbed yours in the bottom on one end then out the bottom on the opposite end. Do you know if there is any kind of sizing rule of thumb as far as wood boiler water capacity to how much water capacity you can have in your radiators?

How does the radiator ge full of water when both are piped in the bottom??:confused:
 
How does the radiator ge full of water when both are piped in the bottom??:confused:

As you and Darnet both posted above I will need a bleeder at the top of the outlet side of each radiator. Would that not bleed all of the air out when you fill the system?
 
As you and Darnet both posted above I will need a bleeder at the top of the outlet side of each radiator. Would that not bleed all of the air out when you fill the system?

The bleed valve won't work properly if the supply and return are both piped in the bottom. The water would just come out one pipe and flow into the other. You need to put the supply in the bottom and return in the top. This would allow the ratiator to fill all the way up with hot water. Then the bleeder vale will need to be used to evacuate all the air in the radiator. If you don't bleed off all the air you can cause an air lock which will not let the water flow.
 
I have converted many steam systems to hot water, Darnet is correct plumb both supply and return into the bottom of the radiator and a bleeder in the top. If there isn't already a plugged 1/8" hole on top side of one of the end sections for the bleeder, there will be a small round flat spot where you can drill and tap it. Most time you can get away without having the radiators flushed to have some one do this is very costly. There are additives you can use that will help with the scale
 
All my radiators are full of water. When you crack the bleader water will come out. This is how the plummer had me hook them up. If they were draining because the outlet is hooked up on the bottom they would get air bound all the time. So far I have had no problems with that. Just to let you know this is a closed system now. The pipes and radiators and header are full of water all the time.
 
I have converted many steam systems to hot water, Darnet is correct plumb both supply and return into the bottom of the radiator and a bleeder in the top. If there isn't already a plugged 1/8" hole on top side of one of the end sections for the bleeder, there will be a small round flat spot where you can drill and tap it. Most time you can get away without having the radiators flushed to have some one do this is very costly. There are additives you can use that will help with the scale

Sorry for being a pain. How would the bleeder bleed the air when the air won't push through if they are both piped in the bottom?? How would the radiator get full of water to have max heat transfer??
 
All my radiators are full of water. When you crack the bleader water will come out. This is how the plummer had me hook them up. If they were draining because the outlet is hooked up on the bottom they would get air bound all the time. So far I have had no problems with that. Just to let you know this is a closed system now. The pipes and radiators and header are full of water all the time.

A plumber works on plumbing kinda things. Ask a pipefitter how to hook it up.
 
I think these radiators were two pipe as they have a pipe attached on both ends at the bottom. One is larger which I assume was the steam supply and the other end has a smaller pipe which I assume was the water/condensate return back to the boiler. Does that sound right?

You are right hedgecutter.

A one pipe system would have been for steam supply as well as condensate return. The pipes have to be sloped properly to work this way, and it went out of practice due to the restrictions on pipe runs. The two pipe system had the steam in and condensate out like you mentioned. Typically the condensate return line is a few inches above the bottom, so that any of the crud that would flake off or settle out of the steam would become trapped in the bottom of the radiator. That way it wouldnt plug up your condensate return line.

Here is a page worth a read....

http://www.masterplumbers.com/plumbviews/2000/convertsteama.asp

And Another...

http://search.thisoldhouse.com/search.html?Ntt=radiator&bu=
 
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