Grundfos 15-42F Speed Question

Jim_52

Forgot to ask, what is head loss? THe highest point of piping is about 5 feet above the circ pump, connecting to the garage heater hanging from the ceiling.

Jim_52

Grundfos 15-42F Speed Question

Can anyone tell me what the three speeds are on the Grundfos 15-42F circ pump, and what it should be on? Mine's been on "2" for years, but recently I discovered that changing it to "1" makes it much quieter inside the house. On "2" or "3" there is a very slight rumble or moan that can be heard in certain parts of the house. I have one zone, with an open loop in the garage for the heater, so it's circulating unless I turn off the breaker to the boiler. 1982 Burnham 204. Thanks.

Brad White_52

Depending on your head loss

I cannot find the RPM values corresponding to the speed settings. I would think your Burnham would run nicely at about 8 GPM (96,000 input, 78K and change output call it 80K at a 20 degree drop.)

Assuming that is right and constant for discussion, you would have head loss capacity of 2.5 feet on speed 1, 7.5 feet on speed 2 and 12 feet on speed 3

If your piping is an old converted gravity system speed 1 might just do it. If iron pipe maybe 1.25" even in a monoflow system, speed 2. (Mine was like that for years is how I know). If small tube copper and long distances, speed 3 and that may be high.

I would try speed 1 and watch the boiler temperature rise to gauge/triangulate the flow. If it works and heats well, what's not to like? I kind of doubt it will be enough flow but give it a try.

Grundfoss circulators are usually very quiet in and of themselves. But a restriction at the outlet, sharp turn, flow check valve.... regardless of circulator brand, anything turbulent may create some noise as a function of flow. Noise travels really well in water, an incompressible fluid. Shows up in odd places. I have it show up in one of my Runtal wall panels but only since the Pressure Accident that turned that one into a mattress. (I do not talk about that anymore. It is too painful

Jim_52

Thanks for the input. The house is 1982 ranch style. All copper pipes, baseboard above and in crawl space (live in Alaska) P204 Boiler mfg'd in 1979 I believe. No outdoor reset, so I keep the temp around 160 until zero or colder. If I slow it down, the boiler temp might go up?

Plumb Bob

The head loss is unrelated to the highest point in the house; it has to do with pipe diameters.

The pump doesn't have a fixed RPM at each speed; it depends on the head. So your question does not have a simple answer. In general, the pump speed doesn't matter a whole lot as long as it is heating the house adequately. So if pump speed #1 works for you, it is probably fine. (Mind you, I haven't seen the house and can't anticipate esoteric problems.)

No, the pump output (supply) temperature won't go up, because the boiler has a fixed supply temp set by its aquastat dial. However, the temperature of the returning water will go down. You can think of it this way: if the water is moving more slowly, it has more time to cool down in the radiators. So the difference between supply and return, the delta-T, goes up. But this doesn't matter than much; people say delta-T should be about 20F, but there is nothing sacred about that.

soot_seeker_2

Any changes in the heat around the house?

If no changes, I'd leave it on one.

Jim_52

Nope - All is well so far

Jim_52

Learned that when

the zone valve is open to the house, the noise diminishes almost completely in the house, but not right by the boiler. Makes me think bearings...?

Jerry_15

All great advice, but if you check the delta t, it will tell you in an instant if you're over pumping. Folks tend to over pump baseboards, and under on infloor. You have the luxury of an adjustable pump. 15 to 30 great. 5 you're wearing the copper off the pipes, and creating velocity noise. 40/50, acid rain in the boiler. Good luck

Jerry_15

Oh yeah, check the pressure on the system, rumblng is often a sign of low pressure. DON'T TRUST THE BOILER GAUGE. Stick a test gauge on the boiler drain. Good luck.

Paul Pollets

PBD

Jim, If you install a Pressure Bypass Differential valve around the pump, you'll eliminate all pump noise and when the zone valves close down, the pump's energy will be shunted to the return, rather than "dead-heading" the pump. PBD's are made by Honeywell, Oventrop, Danfoss....

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