maximum copper pipe length

Joe R

Regarding the 55 to 73 feet of element, sounds like it would be enough. But 150 feet round trip, maximum copper pipe in the system wouldn't work because there are several rooms (built 1949) to be served, (or did I get it wrong) and you were saying maximum 150 per zone? Obviously the pump would have to have the ability to move eveything.

Joe R

maximum copper pipe length

What is the maximum length of 3/4 inch pipe that one can have in a hot water system including how much can be finned radiation. A heat loss has been calculated; the boiler is 101,000 btu; the house is 2800 sq ft plus 1100 sq in the basement. I want to heat the basement and get rid of the electric baseboards on the 2nd floor as well as improve some 1st floor locations.

Brad White_9

In a single run??

It all depends on how the radiation output is sized.

Firstly, for your situation, I imagine you will be splitting up each area on separate zones. (Duh, you must, for you are an intelligent being with opposable thumbs


Back to radiation selection: If selected for 180 degree water (170 average given a 20 degree drop), a 3/4" line can comfortably handle 3 to 4 GPM. I would not go higher.

Finned element varies by manufacturer and application so that can range from 500 to 650 BTUH per LF, sometimes more. Let's take it at 550 per LF to be conservative.

Now let's balance the two concepts:

Flow at 3 to 4 GPM and a 20 degree drop allows you 30,000 to 40,000 BTUH to be distributed. At 550 BTUH per LF, you could have between 55 and 73 linear feet of element on that run.

Running 150 feet does not scare me, round trip. If you allow 50% for fittings and such, the pressure drop will be between 5.5 and 9.3 feet of head at 3 to 4 GPM respectively.

Keep in mind that if any loop serves a series of rooms versus one open floor plan, the radiation will have to be derated (element increased) in direction of flow to compensate for temperature drop.

Brad White_9

I was thinking

not over 150 feet per circuit all in parallel.

Yes you could size your circulator for all three and use zone valves and maybe a pressure differential bypass valve or use three parallel circulators with flow-check valves. Your call.

Personally, I favor fewer pumps. The electrical use adds up. You can always toss a couple more hamsters in the generator wheel but the poor guys do get tired, not to mention union scale