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What is \"Feet of Head\"?

Mark115
Mark115 Member Posts: 6
I think the circulator may be too small for my system. I've looked at the TACO 0xx-F5 data sheet. I understand how to read the graph, but I'm not exactly sure what is meant by "Head-Feet" or "Feet of Head".

There's about 20' of 1.5" pipe between the boiler and the 1st radiator in the nearest zone. There's about 40' of 3/4" pipe to 1st radiator in the farthest zone. Is that the information I need to select the right circulator?

Also, if anyone can tell me the recommended gpm thru Buderus G234x-45 and G124x-25 boilers, I need that too.

Comments

  • thfurnitureguy_4
    thfurnitureguy_4 Member Posts: 398


    I believe that feet of head refears to the vertical # of feet your pump is trying to raise water or whatever. Im sure the resistance caused by the length of pipe weighs in but the head is over coming gravety, Lifting water up
  • Al Letellier
    Al Letellier Member Posts: 781
    feet of head

    It is the measure of resistance to flow through any given piping system. To figure the "head", measure the longest run of piping in the system (from the boiler and back), add 50% and then multiply by .04. That will give you the head. If you have a commercial pump and can measure the pressure on both sides of the pump, find the difference and multiply by 2.3 and you have your system head pressure. It's simple math.

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  • Jim Walls
    Jim Walls Member Posts: 49
    pump head

    is the force the circulator develops to overcome pressure drop, it refers to the circulators ability to over come friction,,,,,,,,in other words you must take into account the number of fittings, & the size of the pipiing network,,,,,,,as for as the circulator is concerned the height of the system does not exist, that is static pressure and has no affect on the circulator,,,,,,,,,lifting the water is a function of the feed valve,,,,,,,
  • Jed_2
    Jed_2 Member Posts: 781
    Circulator Head

    The pump curves you are seeing represent the potential feet of mechanical head energy that particular pump is capable of developing, depending on the piping circuit resistance to flow, expressed in "feet of head". Use the methods expressed in other posts to estimate your circuit, and choose the appropriate circulator.

    Jed
  • thfurnitureguy_2
    thfurnitureguy_2 Member Posts: 74


    The weight of the water going up is counteracted by the weight of the water going back down in the sealed system. Is this why its static?
  • Steamhead
    Steamhead Member Posts: 16,714
    Also

    the amount of actual resistance the water encounters will depend on how much water you're trying to move thru the pipes. This is the reason we should use such small circulators on gravity conversions- the pipes are large, the flow rate is low, so the resistance is low.

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  • Mark115
    Mark115 Member Posts: 6
    How much is too much?

    My system has 1 circ pushing into the boiler, and I have 5 zones. Recommended flow thru G124/25 is 10gpm. Typically, only 1 zone calls at a time, but it's rare that more than 2 call at a time. Zone1 is easily the most active.

    I've calculated my FTHD and the gpm generated by a TACO 0011 on each zone:

    Zone1: 10.8 FTHD, 22gpm
    Zone2: 9.0, 23
    Zone3: 6.6, 24.5
    Zone4: 7.2, 24
    Zone5: 6.0, 25

    Are these flow rates simply too high?
  • Steve_35
    Steve_35 Member Posts: 546
    Feet of head

    is just a way of quantifying how much resistance to flow a pump can overcome. Of course this will vary as the amount of fluid being moved through the pump changes.

    A pump that can move 5gpm at 10' of head can literally move 5 gpm of water out of the end of a pipe that's 10' above the pump outlet. If you need to move 6gpm you may have to shorten the pipe to 9'.

    As far as flow through a cast iron boiler like these it's generally not the concern it is with a condensing boiler. What is a concern though is making sure the return water gets hot quickly enough to not make these condensing boilers. You mentioned radiators. If these are cast iron with iron piping this would probably be a concern.
  • Steve_35
    Steve_35 Member Posts: 546
    What size are the pipes?

    You want to stay under 4fps.
  • jim walls_3
    jim walls_3 Member Posts: 31
    static

    thfurnitureguy,,,,,,,,,,,,,,sorry it took me so long to reply,,,,,,you are correct,,,,,,The first time I attended a seminar of Dan's, I think he was still sponsored by B&G, and they have this great little book they handed out at the seminar titled "It Ain't the Same!" (CounterPoint) "How Hydronic System components Really Work"
    It is written in wonderfully plain English, just like Dan's books,,,in fact I'm not sure that he did not have a hand in this or write it himself,,,,

    In one section "Circulator's Job descripition", along with illustrations you are asked to think of the circulator as the motor on a ferris wheel. A Ferris wheel motor does not provide lift, the weight going up is balanced by the weight coming down. The motor's only function is to overcome the friction of the bearings and the air to set the wheel in motion. So a circulator only has to overcome the friction in the piping system to set the water in motion as the weight(static pressure) is perfectly balanced with the same pressure going up as coming down, as you mentioned,

    Hope this is helpful
    Jim
  • Mark115
    Mark115 Member Posts: 6
    Cast iron - yes

    The longest loop is 1.25" cast iron pipe and bb. Everyone says that they suck more heat out of the water than copper bb, but no one can tell me how much.

    Please check my calculations: 10 gpm = 2.6 ft/sec thru a 1.25" dia pipe. I should be OK thru the iron, but 10 gpm thru the 3/4" copper bb is 7.2 ft/sec. Is that a problem?
  • Mark115
    Mark115 Member Posts: 6


    Great information guys! Thanks!
  • ALH_3
    ALH_3 Member Posts: 151
    Head

    Water weighs 62.4 lb/ft^3

    According to Daniel Bernoulli:

    Divide the pressure in lb/ft^2 by 62.4 lb/ft^3 and you get ft. This is referred to as "pressure head".

    Divide the fluid velocity squared by 2*32.2ft/s^2 and you get ft. This is "velocity head".

    Simply subtract the final elevation from the initial elevation to obtain "elevation head"

    Pumps work by creating velocity head and converting it to pressure head.

    To convert psi to ft of head multiply by 144/62.4 (1psi=2.3066ft)

    Head loss is fairly complicated, but it essentially has two sources: shear stress at the pipe wall and turbulence at irregularities like valves and fittings. There are all kinds of short cuts to estimate these values, but it depends on the material of the pipe and the type of valves and fittings present in the system.

    -Andrew
  • Steve_35
    Steve_35 Member Posts: 546


    10gpm through 3/4" copper is WAY excessive. Velocity should be 2-4fps according to people much smarter than me.
  • Joe Mattiello
    Joe Mattiello Member Posts: 703
    Feet of head is unit of measure for pressure

    Centrifugal pumps use ft of hd,as opposed to psi. the conversion is divided by 2.31 to psi. the pressure in the system or the system curve is calculated by the flow rate required through a length of pipe at the diameter specified, plus valves, fittings, and the pressure drop through the boiler. Knowing all of this gives the design engineer the operating point of the pump on its curve.

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  • Weezbo
    Weezbo Member Posts: 6,232
    WEll Feet of Head is an Irish term...it evolved over many

    centries...for the most part as near as we have been able to ascertain one takes a 80 gallon beer mug, and pours a full Barrel of stout from height of 6 foot above the mug,....as fast as it can be done...then one takes the yard stick and measures from the top of the stout to the top of the Head.....I hope this helps. if you get it wrong the first time no problem divi up the stuff roight fast and gie er another go .*~/:) Happy Saint Patricks dae.
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