flow restriction

stan_2

Is it or is it not true that the water flow in a hot water system with copper-finned baseboard piped in series is restricted to the smallest diameter pipe in the loop? I recently saw a job where the installer supplied the first piece of baseboard in a loop with 3/4" pipe then reduced to 1/2" which fed the next piece of baseboard. I followed the piping and found that it continually changed back and forth from 3/4" to 1/2". I can only guess why someone would do this. The 3/4" pipe, working with a 20 degree delta T, was fine. I seriously doubt they were working with anything but 20 degrees. I think the answer to my question is yes but I'd like to hear someone elses thoughts. Thanks for any input!

Steamhead

You're absolutely right

that 1/2" piping really slows down the flow. Betcha the end of that loop doesn't heat properly.

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flange

for a given pipe size, x amount of gpm will flow with a predetermined pressure drop. if you are pumping this water, your overall gpm will be reduced, but your velocity will be increased. system delta p will increase, overall performance will decrease. example: when you put your finger over a portion of your garden hose, you cut down on the water coming out of the hose right?, but the water does come out at a higher velocity.

randy_4

1/2 pipe

You can run up to 25 feet of baseboard in a 1/2 loop which will stay in the 20 degree temperature drop. Most supply companies stock 3/4" baseboard, so you'll find the piping to the baseboard in 1/2" and the baseboard element in 3/4".