Heating loop length

Paul_28

What is the maximum length heating loop the can be made with ¾ inch copper pipe?

Mike T., Swampeast MO

Like most things in hydronics the answer is, "it depends."

But, using the below generally regarded "safe" parameters of:

1) 20° temperature drop in the loop

2) 1 gpm flow

3) 170° AVERAGE water temperature (assumes 180° supply and 20° temperature drop)

4) 480 btu/hr per foot of baseboard (65° entering air)

--------------------------

One gallon per minute of flow @ 20° temperature drop gives you 10,000 btu/hr to work with.

10,000 / 480 = 20.833' of baseboard max @ 1 gpm.

--------------------------

With 2 gpm of flow @ 20° temperature drop you get 20,000 btu/hr to work with.

20,000 / 480 = 41.666' of baseboard max @ 2 gpm.

--------------------------

With 3 gpm of flow @ 20° temperature drop you get 30,000 btu/hr to work with.

30,000 / 480 = 62.5' of baseboard max @ 3 gpm.

--------------------------

With 4 gpm of flow @ 20° temperature drop you get 40,000 btu/hr to work with. 4 gpm is the the highest recommended flow rate and baseboard output can now be considered to be 510 btu/hr per foot with 4 gpm of flow.

40,000 / 510 = 78.43' of baseboard max @ 4 gpm.

--------------------------

To compute flow you must first find the head loss in the loop including all fittings, etc. Then select a circulator that will move the desired amount of water at that head loss.

--------------------------

If you design for a 30° temperature drop in the loop (again considered near the maximum safe design level) each gallon per minute of flow will now move 15,000 btu/hr. BUT, the average temperature will now be lower at about 165° (assuming 180° supply) so each foot of baseboard will be putting out slightly less heat.

Paul_28

Thank you

> Like most things in hydronics the answer is, "it

> depends."

>

> But, using the below generally

> regarded "safe" parameters of:

>

> 1) 20°

> temperature drop in the loop

>

> 2) 1 gpm

> flow

>

> 3) 170° AVERAGE water temperature

> (assumes 180° supply and 20° temperature

> drop)

>

> 4) 480 btu/hr per foot of baseboard

> (65° entering

> air)

>

> --------------------------

>

> One gallon

> per minute of flow @ 20° temperature drop gives

> you 10,000 btu/hr to work with.

>

> 10,000 / 480 =

> 20.833' of baseboard max @ 1

> gpm.

>

> --------------------------

>

> With 2 gpm

> of flow @ 20° temperature drop you get 20,000

> btu/hr to work with.

>

> 20,000 / 480 = 41.666' of

> baseboard max @ 2

> gpm.

>

> --------------------------

>

> With 3 gpm

> of flow @ 20° temperature drop you get 30,000

> btu/hr to work with.

>

> 30,000 / 480 = 62.5' of

> baseboard max @ 3

> gpm.

>

> --------------------------

>

> With 4 gpm

> of flow @ 20° temperature drop you get 40,000

> btu/hr to work with. 4 gpm is the the highest

> recommended flow rate and baseboard output can

> now be considered to be 510 btu/hr per foot with

> 4 gpm of flow.

>

> 40,000 / 510 = 78.43' of

> baseboard max @ 4

> gpm.

>

> --------------------------

>

> To compute

> flow you must first find the head loss in the

> loop including all fittings, etc. Then select a

> circulator that will move the desired amount of

> water at that head

> loss.

>

> --------------------------

>

> If you

> design for a 30° temperature drop in the loop

> (again considered near the maximum safe design

> level) each gallon per minute of flow will now

> move 15,000 btu/hr. BUT, the average temperature

> will now be lower at about 165° (assuming 180°

> supply) so each foot of baseboard will be putting

> out slightly less heat.