pump volume

Brad White_185

at least to verify your outcome:

What is the space's heat loss and how much radiation (finned element) do you have?

<i><b>The question of how much flow you can get through 1.25" pipe is one thing, the fin tube flow requirements to make rated output may be something else entirely...</B></i>

The table of outputs for the radiation will be your best guide and the only place I would start.

Say you have 4.25" fins on 1.25" nominal copper at say 1,000 BTUH per linear foot and a space heat loss of 40 MBH. Technically, at a 20 degree temperature drop, you need 4.0 GPM.

Your flow velocity is below 1 FPS and being below the magic number of 3 FPS that will marginally affect your output. There are charts which depict an accelerating drop-off below 3 FPS but this does not become appreciable until you get below 1 FPS in general terms. As a practical matter, maybe you increase the flow to get away from the laminar flow range.

BTW: The reason I mention and used "40 MBH or 40 feet of element" is that this is a guideline I have been trained to use. It is not a coincidence. Longer than this and depending on a variety of circumstances, you can get a colder feeling at the return end and perhaps too warm at the supply end.

Keep in mind that you can quadruple your flow rate and barely add 10 percent to your output; all doing that does is to very slightly raise your average water temperature upon which the radiation is rated, right in the middle of the run. Try to save pump Watts...

Here is a tip for greater comfort, not that you asked: If you are feeding at one end and returning at the other (straight shot), you will have the possibility of "warm at one end, cold at the other". Your average water temperature will be in the middle and will rise and fall on the appropriate side of that.

If you supplied and returned at the same end, with a u-bend at the far end, your average water temperature will be the same no matter where you draw an imaginary line through the elements. Diagram it and see. This can also allow you to better use the flow potential of 1.25" pipe to maximize output. You will not double your output but may just get another 35-50 percent out of it. If you do this, I suggest supplying water to the top element and return along the bottom, to keep the temperature differences as wide as you possibly can. Hope that makes sense!

MaintmanMN

Pump volume

What kind of GPM would be reasonable to put through a 1-1/4" baseboard heat loop? Is there a chart of rough guidelines.

ALH_4

Velocity

The maximum flow rate is generally limited by velocity because of pipe/fitting erosion. Also as the velocity increases the required pump size increases. I like to stay below 5 ft/s in general. You're looking at 19gpm max at 5 ft/s in a 1-1/4" pipe.

John Faust

The rule of thumb is not to exceed 4 ft per second velocity. This is to keep noise level low and secondly to reduce pump head. At 4'/sec this would be 15 gpm in copper. The copper development association has sizing calculators avaialble.