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tmguinan 09-22-2012 04:55 PM

Pipe Sizing for Hot Water Heating System
I live in an old house where we recently replaced our heating system hot water boiler. The original system in the house was actually steam heat and the previous and current system use hot water which is circulated through the old massive steam heat pipes. We would like to replace these with copper or PEX pipes. Was thinking we would use 1 inch piping on main supply and return pipes and 3/4 inch for connections to the radiators. Does this sound about right?

beenthere 09-22-2012 06:25 PM

1" copper is good for about 80,000 BTUs. So what size is the boiler, and how much radiation do you need for the house.

tmguinan 09-22-2012 08:17 PM

Many thanks for the quick response. The boiler is rated at about 93,000 Btu output. When I did a radiator calculation I came up with about 100k btu. I called the manufacturer and they told me the boiler was adequate for the house. Your number troubles me a bit as the piping the plumber installed to connect the furnace to the old piping is 1 inch copper - seems that might be a bit on the low side. Haven't faced a cold winter yet- it was installed early last spring.

beenthere 09-22-2012 09:27 PM

Hot water boilers should be sized to the homes heat loss, not the amount of radiation, as most home have more radiation in rads then needed. Your boiler should have been connected with 1-1/4" copper. 1" will probably work. But its FPM will be slightly higher then it should be.

tmguinan 09-23-2012 07:09 PM

Thank you for the excellent information. To tell u the truth I'm puzzled why the plumber didn't us the correct size pipes. Since he was not repiping the house and just connecting to the existing loop, how much money could have been involved. My suspicion is that he just didn't know what he was doing. - troubling. If I change the main loop I will go with 1 and a 1/4 inch piping and replace what he did n the furnace.

beenthere 09-23-2012 07:28 PM

Shame is, Could be he didn't have any 1-1/4" on his truck.

tmguinan 09-23-2012 07:55 PM

I have one more question, if you don't mind. The plumber installed his own circulator, not the one that was shipped with the unit. Seems to work fine, but I noticed the top of the connection flange is 1 inch as u might suspect. Does this mean I will likely need a circulator with a 1- 1/4 flange? Not sure how these things a manufactured.

beenthere 09-23-2012 07:59 PM

You'll need 1-1/4" flanges. The circ should be fine.

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