Boiler circulator pump question


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Old 01-02-10, 06:59 PM
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Boiler circulator pump question

Here is my situation:

I have a c. 100 year old house with new windows and improved insulation, but it still leaky. The house is 3 floors + basement, approx 3000 sq ft.

We have a 3 year old radiant hot water system. The boiler is a Slant/Fin Victory II 120,000 BTU boiler, no domestic hot water. I am currently running at about 18 PSI, ODR is using a set-point of about 120 F, outside temp is currently about 5 F.

Last year we had the boiler re-piped, as the installers had put the circulators on the return side. We moved them to the supply side as well as adding an ODR. This reduced (but did not eliminate) creaking noises and stopped the short cycling of the boiler. Our gas bill dropped about 20% as a result.

There are 3 zones piped with 3/4" pex and an Armstrong Astro 30 pump, one zone per floor (basement is not heated directly). On each floor there is a manifold that divides the line into 4 loops using 1/2" PEX in a staple-up installation for each of the first two floors and 2 loops for the 3rd floor (which is about 1/2 the size of the other floors).



Here's the problem:

The third floor is quite cold and based on the flow gauges on the manifold I am getting about 1 GPM per loop. If I shut off one of the loops, I get closer to 2 GPM in the other loop.

My question:

From what I understand, the Astro 30 pump performance curve tops at about 16' of head and only 13' of head at 4 GPM. If I replace this with an Astro 50 or 70 (20' and 23' @ 4 GPM respectively, will I solve my heat problem?

I don't know what the delta is on this zone, but subjectively it feels much greater than the other two zones.

Thanks for any advice.
 
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Old 01-02-10, 07:38 PM
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Delta T's would be idea to have.
On first look, sounds like either there is a bit too little tubing.
1000 sqft * 1.6 = 1600 /4 = 400' loops.
400 foot is a long loop, so I don't think anyone would install that much pipe.
PEX is BAD for staple up, and 120 degree water temp might be too low.
At 1 gpm, you have about 3.61 ' hd per 100 ft.
You might try to trim the flow on the two zones that are making temperature and send some extra flow up to the third, then bump the temp a bit and see where you go from there.

Typically I will use a Taco 00R or a Grundfos 15-58 for applications such as this without issues.
 
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Old 01-02-10, 07:50 PM
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I agree with you on the staple-up PEX! We bought the house this way- it was newly renovated.

Unfortunately, I do not have the plans so I can't even figure out where the loops are run on each floor. On the first and second floors the loop servicing the area farthest from the manifold are still too cold, so I am reluctant to cut flow down there. I may try bumping the water temp 5 degrees and see if it helps.

Can I replace the Armstrong pump without re-piping? That is why I thought of swapping for the more powerful Armstrong that fits in the same space.

I have been unable to find a pro in Toronto who really understands this kind of system. I have gone through two companies that don't really get it - I have been trying to educate myself on this as I go.

Originally Posted by TOHeating View Post
Delta T's would be idea to have.
On first look, sounds like either there is a bit too little tubing.
1000 sqft * 1.6 = 1600 /4 = 400' loops.
400 foot is a long loop, so I don't think anyone would install that much pipe.
PEX is BAD for staple up, and 120 degree water temp might be too low.
At 1 gpm, you have about 3.61 ' hd per 100 ft.
You might try to trim the flow on the two zones that are making temperature and send some extra flow up to the third, then bump the temp a bit and see where you go from there.

Typically I will use a Taco 00R or a Grundfos 15-58 for applications such as this without issues.
 
  #4  
Old 01-02-10, 09:52 PM
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"MOST" wet rotor circulators have the same flange to flange spacing, at least until you get into the bigger pumps.
Hopefully, the installer put shut offs on either side of the circ so it does not require draining.
ODR helps a great deal with the ticking of the pex, but as you increase the water temp you will get back into the start and stopping of flow and you will get more ticking.

I only ever did two jobs with PEX staple up, one was for a business so the tick didn't matter, and the other for a friend in the beaches and he didn't have the money for Onyx tubing.

Let me know if there is anything I can help you with.
 
 

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