Velocity Noise - Possible Oversized Circulator?

topher77s

Just a homeowner here looking for some advice. I've been hearing a lot of velocity noise (sounds like water rushing through pipes) in my hot water baseboard heating system. I am beginning to wonder if the circulator (Grundfos UPS 26-99 on the lowest speed) is oversized. My system is a single zone of 3/4" fin tube baseboard that splits into two loops off a 1" supply main in the crawlspace. Both loops feed back into a 1" return main in the crawlspace. The first loop measures 82' of fin tube element and about 90' of additional piping, the 2nd loop has 78' of element and 70' of additional piping . In addition to the baseboard zone, the circulator is also feeding a Burnham Alliance 35 gallon indirect water heater. The baseboard zone and indirect are zoned with zone valves.

Some additional details: House is a 1670 sq ft. ranch. Heatloss from SlantFin app calculated at 68,000 BTU. Boiler is a Solaia SL375 with a Carlin EZGas burner.

I've been reading through some of the posts on the wall about circulator sizing and after looking at pump curves, I'm thinking the UPS 26-99 is too large for this system. I'm wondering if a UPS 15-58 or maybe an ALPHA would be a better fit? I'm open to suggestions. Thanks!

Zman

What speed is the 26-99 set at?
Doing the quick calculation, at low speed the circ is a little too big, probably not worth replacing. At high speed, it is way too fast and will cause pipe noise and erosion issues.
Something like the 15-58 or alpha would have been a better choice.
Sometimes the noise you hear is air trapped in the pipes. What is the system pressure? Is the the circulator "pumping away" from the expansion tank? Pictures would help.
Carl

Paul48

The 26-99 on low is about perfect for the system. Four gallons per minute to each part of the split loop at 10 ft/hd. I think your problem is balancing the split loop.

Zman

Paul48 said:

The 26-99 on low is about perfect for the system. Four gallons per minute to each part of the split loop at 10 ft/hd. I think your problem is balancing the split loop.

When I put it Siggy's software on low it was around 5.5 gpm on one side and 4.3 gpm on the other. That is in the right range (upper end).
Moving to the 15-58 or alpha had it in the 3-4 gpm range.
Kind of a personal preference, in my mind there is not a clear right or wrong.

topher77s

The circulator is set on the lowest speed and is pumping away from the expansion tank. There is a bypass loop with a thermostatic bypass valve for boiler protection. The pipe noise is audible when the circulator is on low and is of course much worse when on either of the two higher speeds. It sounds like water running through the pipes kind of like what you can hear from another room when someone is running water elsewhere in the house. System has been purged of air through the purge valve and no air comes out when opening individual bleed valves on the baseboards. System pressure is reading about 20psi cold and about 25psi hot if the gauge on the boiler is correct. Seems a bit much for a ranch?

I've attached a couple pictures of the boiler.

Zman

If it were mine and the noise was an issue, I would switch it for an alpha.
The advise Hatterasguy gave you about checking the supply and return temps would be a good step before spending money on a new circ.

topher77s

Thanks for the replies! I'll get the installer to check the supply and return temps when he comes to service the boiler and swap the circulator out if necessary.