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[GCTerpfan]

Last winter I was getting a larger temperature drop coming back to my stove than I wanted, because of this I decided to upgrade the circulator on my stove.  I used the information from this link to determine what pump I needed: http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf

I have one circulator on my stove and it sits fairly large distance from my house and my garage.  I have a total loop from stove to house to garage and back to stove of 420' of 1.25" pex.  I am not currently heating my garage but hope to in the future.  Lets assume I need 100,000 btu/hr with a 20 degree delta T, this means I will need a flow of 10gpm.  This is just under the maximum flow of 1.25" pex, which is 11.2gpm according to the link above.  I have a total loop of 420' and I have calculated the equivalent length of the piping circuit as 513.5' with all valves, tees, elbows, etc.

I have calculated the head loss as 21.4' in step 4 and I added 6' because my stove sits 6' lower than my house.  So the total head is 27.4' and I need 10gpm which hits the 0013 pump curve almost exactly.

Here is the problem, I heated last winter with the 007 pump that is currently on the stove.  This spring I pulled a fitting off in my garage (which is near the end of my piping loop) and filled a 5 gallon bucket in about 45 seconds.  This means the 007 was pumping about 6.6 gpm, but according to the pump curve the 007 pump should not have been providing any flow at all at 27' of head?  According the pump curve it was operating under 8'-9' of head if it was pumping 6.6 gpm. What am I doing wrong?

[juddspaintballs]

Is any part of the system higher in elevation than the fitting you removed to fill the bucket?

[GCTerpfan]

Yes. The fitting was about 4' lower than the highest point of the system. I am guessing it may have been syphoning?

[juddspaintballs]

Draining out, yes.  Gravity is a heck of a water pump.

[willieG]

i think your 007 on that length of loop would be able to do somewhere between 5 and 6 gpm
i think you would be between 8 and 9 feet of head

as your desire for gpm increases or decreases (and your loop stays the same length) the head pressure created will also increase or decrease

[RSI]

The elevation should not be figured into the total head.
It will screwup the flow rate running into a bucket though. You need to get the end of the pipe at the exact height of the top of the water in the boiler for that to work.

I just estimated what the 007 would be flowing and came out the same as Willie's estimate. My guess is closer to 6 gpm.

An 0011 pump should get you over the 10GPM you are looking for. Unless you really want a taco, I would go with a Grundfos 26-99. They are better pumps (in my opinion) and you can get them for less money right now due to special pricing Grundfos had at the end of last year.
Also, it is a 3 speed pump so you can run it at a lower speed if you find you don't really need that much flow.

[GCTerpfan]

Thanks guys, it makes sense now. I failed to realize that the flow rate is  a component of HL, so as the flow goes down so does the head and vice versa. 

I was also looking at 3 speed pumps but couldn't find any pump curves to make sure they would work.  I have read good things about Grundfos and I have no attachment to Taco, so I will check them out.
Thanks.