What size circulator pump for boiler?


Old 01-01-18, 04:58 AM
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What size circulator pump for boiler?

I have long loops. First floor about 150 feet. Second floor about 175 ft. Master bedroom, about 150, Basement, 120. I have baseboard. The boiler is in the basement. 178,000 BTU with efficiency of 85%. What I have trouble understanding is the curve chart for a VT2218 circulator pump. Looking at 00e Series VT2218 | Taco Comfort Solutions I figure that to get to the top floor, that is about six feet up from boiler to the first floor, then eight more feet up, plus one foot more between floors. So that is 15 feet. Throw in the various elbows and maybe it is 17 feet. So the chart shows at speed 4, there is your 17 feet reached at four gallons of flow. I have 3/4 inch pipe. But what about the basement or first floor? At that speed, if I understand the chart...the flow of water would be too fast. It seems a smaller circulator like the Taco 7 is fine for the first floor but not for the second. Flip that around, what can pump to the second floor seems to be good for the second floor and not the first. What am I missing? And if a few zones open up at once like in zero weather, how does the hot water get up to the second floor? I must be misinterpreting the chart. Anyone who could set me straight, thank you. My goal: have circulation upstairs and not starve upstairs but not cause pipe damage on lower levels with a constant speed.
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Old 01-01-18, 05:56 AM
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The static head involved in the elevation difference up to your top floor is irrelevant, except to initially fill the system, which you can use city water pressure for. Then when the circulator is running, it only sees the differential head of the dynamic friction loss of the piping. What is the current pump and how well does it perform? Why are you replacing the current pump?
Old 01-06-18, 03:42 AM
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I am not replacing the pump. My interest is understanding how the bedroom floor gets equal pump time vs. the basement. There was a time when it was difficult to get heat upstairs to the bedroom floor but no problem with the basement. By problem I mean with weather like recently, I could get it to 68. The basement zone was blasting. The first floor, I could get it to 70 with weather like today. When the inlaws slept over, they liked more heat and I could not give it to them. So I went for a Delta T VT2218 pump but the sensors are too short on one side to get to the supply. So I used the first speed. I am getting good results.

Why Delta T? I was hoping the pump could sense when all zones were open and calling for heat. I wanted a pump that would speed up and not struggle to get heat to the basement floor. I realized I do not understand the pump curves and this is what I am asking. Regarding the boiler, it is at 24 lbs pressure, steady, a Peerless, and the nozzle was changed over the summer from 1.25 to 1.5 and that really made a difference these cold days. So that is the history, and why I swapped the pump last year. I am getting good heat now but it seems to me I do not know how to select a pump as in "How does the bedroom floor not lose out for heat when all the zones are open" and"how is a replacement pump sized?
Old 01-07-18, 06:26 PM
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There are multiple question here. DeltaT pumps have their place, but in multi zone systems lack flexibility. Other brands of ECM circulator pumps are multi mode. The Grundfos Alpha by pushing a button can be set up on seven different speed, pressure or automatic modes. You can experiment and pick the mode best for a given system. It is more practical than playing with pump curves.

Replaced a big Bell & Gossett Series 100 with Grundfos-Alpha for $175:

If system uses zone valves rig up some way ( I use LEDs pilot lights) so you can see which (often several) are activating circulator.

Get a cheap 2 chanel digital thermometer to monitor deltaT, boiler out and return temps, under different modes and zone openings.

It is very cold here. Wife said radiators are not getting as hot as previous years (she is scientist). Showed her 180 F water temp, 28 F deltaT and 5 GPM flow rate. Turns out she had not vacuumed the radiator elements this fall.
syd81 voted this post useful.

Last edited by doughess; 01-07-18 at 07:00 PM.

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