Parallel 1/2 Of 3/4 Copper Pipe

Old 05-10-05, 03:57 AM
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Parallel 1/2 Off 3/4 Copper Pipe

I'm running HOTWATER BASE BOARD (HWBB),3 zones.In one zone I will be running 3/4 with 26 ft of heating elements (HE). Can I run 1/2 copper pipe to feed 3 ft of HE in parallel to this 3/4 section (not in series). The 3 ft will be about 50-60 ft round trip to the 3/4 (trying to run in walls-ceilings).If I can how far should the two T's (on the 3/4 pipe) be apart if it makes a difference. This parallel section will be near the begining of the run of the 3/4.

Last edited by BOB1934; 05-10-05 at 05:12 AM. Reason: spelling
Old 05-11-05, 01:58 AM
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Parallel 1/2 off 3/4


Many older hot water piping arrangements were originally installed this way, & usually work to a greater or lesser degree; in any event, you would have to install at least one DIVERTER VALVE, usually in the return side of your loop arrangement in order to get enough hot water to flow from the 3/4" "main" thru the 1/2" & 3 foot baseboard loop; the supply & return takeoffs from the 3/4" "main" should be at least 1 ft. apart, preferably 2' to 3' apart.

The diverter valve has an arrow stamped on the brass housing as an installation guide; some of them have "supply" or "return" stamped on the housing to indicate installation on either side of the loop.

If you are retrofitting the 3' BB onto a 1/2" piping loop that is already installed in place thru the walls & ceiling & are unable to run either 3/4" (preferable size) copper or flexible PEX plastic to the site of the BB, you might be able to use a diverter valve on both the supply & return of the loop to get enough hot water flow in the 3' BB for your needs, but you might only get ~3/4 gpm flow, which would produce ~400 btu/hr per foot of BB; if you use 3/4" pipe, you would get ~580 btu/hr per ft. of BB.

Also calculate the BTU OUTPUT you need for the room in question by doing a heat loss calculation at the website below; 3' of baseboard is not going to provide very much heat (1200 to 1740 btu/hr); even a small room 10' X 5' (assuming 8' ceilings) in the dead of winter will require ~2250 btu/hr (rule of thumb: 10' X 5' = 50 sq.ft. X 45 btu/sq.ft. = 2250 btu/hr/560 (btu output of each ft. of BB) = 4' of BB needed.

If you're trying to heat a bathroom, the amt of BB should be increased by 50%.

Baseboard is rated according to the temp of the water & the gpm flow thru it; avge is 590 btu/hr per ft. @ 4 gph flow @ 180 degrees water temp.; there is a HIGH CAPACITY output version BB available that puts out 850 btu/hr under the same conditions; this is good for cramped conditions like a bathroom.

The Heating Help website explains the use of piping loops, pipe sizes & diverter valve placement; click onto the "Heating Q & A" item at the sidebar, then onto "Diverter-tee hot-water heating" item.

Diverter valves & high output baseboard are avaialble only at heating supply stores & usually not at the big box home improvement stores.

Last edited by Chimney Cricket; 05-11-05 at 02:23 AM.

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