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# How much more head would a buffer tank (water heater) add ?

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Member Posts: 603
edited May 2022
I plotted a boiler's head against the curves of my Grundfos UPS pump. How much more head would be presented when adding a buffer tank with a half dozen 1" 90's and squeeze it thru the 3/4" tank openings of a side-port water heater (a 12 gallon "tall" water heater used as buffer) ?

30+ yrs in telecom outside plant.
Currently in building maintenance.

• Member Posts: 3,354
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Hi, What sort of GPM are you looking at? Better would be to share the system curve so we can see the fuller picture. My old System Syzer gives me about 3.5 GPM for 3/4" type L copper, so you would be turning over the volume of the tank in about three and a half minutes... if than helps!

Yours, Larry
• Member Posts: 22,342
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Idronics 16 walks you through the steps to plot a system curve. Everything in that circuit needs to enter into the calculation. EL, equivalent length of fittings and devices

Then lay the system curve over the pump curve to determine the OP, operating point, which is where the two curves cross
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 603
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Okay. All 1".. I imagined 7 elbows, 2 sideport tees (the "generous pipes" attached to the buffer), a coupla reducers, 2 ball valves, 10' of pipe, and a little glycol at 130f pushed at 7gpm. Ran it thru the formula and got 1.5ft of additional head.
If I add 1.5ft to the pump-vs-boiler curve intersection (on medium speed), that now puts me potentially below the max heating side flow out of the tank. So now I bump the speed up on my 3-speed pump and recalculate using the pump-vs-boiler intersection (on high speed). The new calculation gives me 3 ft of head (in addition to the boiler at that flow speed), and I end up with 7gpm.
Hopefully that ballparks it.

30+ yrs in telecom outside plant.
Currently in building maintenance.
• Member Posts: 22,342
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15-42 is an older model Grundfos, the 15-58 is a newer 3 speed model, the boiler you are considering has a 15-42?
15-58 or some have a 15-62 OEM version on mod cons
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 603
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The Lochinvar Epic (non-combi) needs a field-supplied boiler circ. The 15-42 is my 20 yr old. Lived the first 10yrs on high speed as my secondary circ , then 10 yrs as my primary circ at low speed.

Should I consider replacing it due to mileage ?
No noise from it, but that's a pretty good amount of spin time I suppose.
Retire it and keep as a emerg backup (it could replace either of my Boiler or System circs in a pinch) ?

The UPS15-58 looks like an exact match, if I need one. Thanks.
30+ yrs in telecom outside plant.
Currently in building maintenance.
• Member Posts: 22,342
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Run em till they drop, replace with ECM  style for less power consumption, torquier motor, digital display, when the time comes
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream