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Re: Cast Iron Rads & New Boiler

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Posted by Wayne Bunker on January 07, 2006 at 22:07:20:

In Reply to: Cast Iron Rads & New Boiler posted by Daniel on November 03, 2005 at 11:58:47:

: I have installed a new oil fired boiler (wet leg) in my 80 year old home. I simply added a circulating pump(with check valve) on the supply side and this works fine. What I am wondering about is how I could make the system even more efficient, when I replaced the boiler I did not remove the pipes that lead to the cast iron rads, the way it is set up now is that I have a large diameter pipe that has smaller pipes branching off to the rads and the return is done the same way. I would like to create one zone upstairs and one downstairs, but as it is setup now both floors are supplied and returned with the same large diametre pipes making it so that all rads are fed hot water no matter what floor. Could I replace the large pipes with smaller pipe, could I start with the farthest rad and create a loop with the other rads while coming back to the boiler, I would obviously only loop the rads that I want on a particular zone. Also what would be the best way to create these zones, should I get two zone valves or should I get an additional circulating pump. Also could I use a mixing valve somewhere to control the amount of cold water coming back to the boiler, there is quite a bit due to the number and size of my cast rads (11 total) and it does take a while to heat up all that water. Thanks for any advise.

You have a supply and return system. You should never pipe cast iron boilers in series. The pressure loss would be huge, this would slow the flow through the system, the first radiators would be hot and the last radiators would be cold. If you want a separate zone for the the second floor you will need to run a new supply and return main for the second floor zone and pipe the second floor radiators to these mains. Because of the amount of water involved I would recommend a separate circulator for each zone. A low water volume boiler may require a bypass from the supply to the return near the boiler to keep the boiler temperature from getting too cold.
You say the pipes are large. If they are bigger than say 1 and 1/2 inch in diameter (inside diameter) then they may have been for a gravity system (no circulator). These pipes are oversized for a pumped system. Find a good plumber or a mechanical engineer who can give you some guidance.

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