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pump size help

rich4 Member Posts: 5
 I have a 38/50' garage with 6- 250' loops of  3/4"dara pex on 16"c but last one it is on 12"c do to big doors. they are ran so the inlet is on one end and the outlet is on the other end of building 50' away.The inlet manfoild is 35' of 1" pex with 3/4" by 1" tees about every 6' to hook to loops. I was going to tee in the middle of manifoild or should i go to the end? The outlet manfoild is 35' tee in the same place  + 50'  of 1" to stove, there is also 4-3/4"  by 1"90s .my heatloss is 30000 btu but i would like 50000 to  60000 btu do to big doors open a lot My concrete has 2" foam under it and 6" on all edges rest of building is r50 stove is a 120000 btu hardy wood furnance ,it has 3/4" nipples on it will i have to put 1" to make it work with 1" feed? Stove is level with floor.  Need help on pump size. Total 3/4"pex 1500' total  1' pex 175' 8 3/4' by 1" tees and 4 3/4' by 1" 90s thanks Rich


  • CMadatMe
    CMadatMe Member Posts: 3,086
    Who Did

    May I ask who did the heat loss and radiant design? Where did you purchased the PEX? Planning on any antifreeze in this system?
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • rich4
    rich4 Member Posts: 5
    I did

    The heat loss was done by a company  and i did one on the net..They  was for 0 degree and r 30  The design was mine  i know lot more now..I will run antifreeze if i can run car antifreeze cause i have 55 gal. new..
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited November 2010
    And We Did A

    Radiant heat loss and not a conventional heat loss correct? How did you come up with the design? Better make sure you size that pump based on the percentage concentration of anti-freeze. It changes the head.

    I ask about the heat loss and radiant design because you want pump sizing and cannot size a pump unless we know the parameters you used.  Did we also design for a 10 degree delta-t? Need to know that also for sizing the pump, ie gpm flow rate.  Where did you purchased your pex and what brand is it? From a local supplier or the internet? Need to see it's flowrate capacity based on the percentage of anti-freeze or 100% water.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • rich4
    rich4 Member Posts: 5

    Here  is some info, pex brand is Nibco,the design? I dont know what you mean. antifreeze 30 to 50 precent which is better? I am not sure on heat loss i will have to look, how does it matter  I heat it right now with a 50000 btu ready heater and it heats very easy
  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited November 2010
    A Radiant

    A radiant heat loss is different then a conventional heat loss. There is very little to no convection so the air infiltration rate changes thus lowering the heat loss..That's why the 50K btus heats very easily and why radiant heat is more efficiency than other conventional heating type systems.  Your cramming more btu's then you need. Which means your wasting your fuel dollars and possibly short cycling your heating equipment. Which means wear and tear...

    The design is important because you have to take into consideration the properties of the fluid in your loops lengths for head. It may also effect the water temperature needed to overcome the heat loss. In radiant for a slab application we design for a 10 degree delta-t versus the standard 20 that is used in a baseboard type system. It matters for pump sizing.  The design also takes into consideration the R-Value of the floor surface in relation to the water temp needed at design conditions to heat the space. May I ask what water temp you are currently running through the system? How would you attain the proper water temp needed when you don't have a heat loss or a proper design?

    I searched Nibco's web site via there technical data but cannot find any flow rate characteristics for 100 percent water or glycol (anti-freeze mix) maybe some else here has those to help you out to figure out head. Going to need that water temp needed as design though.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • rich4
    rich4 Member Posts: 5

    Currently there is no water in it i have it plumbed to manifoilds no pump yet. The 50000 btu is a forced air heater. My floor is 4" concrete no coverings my design is pretty much as my first post. There is no fresh air in the building i will need mechanical vent ,very tight building
  • rich4
    rich4 Member Posts: 5
    water temp

    This system is really no design it is just 6 250' 3/4" pex-nibco with 2 35' manifoids + returns and fitings so water temp i dont know,i have a hardy with ajustable water from from 100 to 180 should have advice sooner
  • Ironman
    Ironman Member Posts: 6,890
    Hardy Wood Boiler

    You cannot run the temp in the wood boiler below 150deg, it will condensate in the flue and fire box.

    Also, you're going to have air/purge problems if you connect the unpressurized wood boiler directly to the radiant. The radiant needs to be pressurized.

    I would suggest you put an indirect tank between the wood stove and the radiant. This will allow you to pressurize the radiant and the aquastat on the indirect can control the temp going to the loops while the stove maintains 170 - 180deg. This will also provide a buffer tank to aid the stove when it tends to lag while recovering.

    We install wood boilers regularly and have found this to be the best way to integrate them directly to radiant.

    Of course, you'll need the normal components to pressurize the radiant side and an additional pump, but this could reduce the size of the boiler pump also.

    Like Chris said, you need to post the correct info for sizing.

    Also, be prepared to deal with alot of smoke. That Hardy will smoke like a freight train.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,839
    Aside from the fact that you have chosen a dicy heat source...

    Calculating the head is a relatively simple thing to do.

    With radiant floors, the lower the delta T, the higher the average fluid temperature, and subsequently, the higher the floor surface temperature. Uponor typically likes to see a 10 degree DT for design conditions.

    So worst case, if your loss is 60K btuH, then 60,000 divided by the number of loops (6) = 10,000 btuH/loop.

    10,000 divided by 480 = 20.8

    480 is a constant for water/glycol mixture based on poundage per gallon times 60 minutes per hour.

    20.8 divided by the required DT(10) = 2.08 GPM per loop.

    So the pressure drop of the individual loops would be based on a flow rate of around 2 GPM per loop.

    Add to this the pressure drop in the supply and return piping, which in your case would be 12.5 GPM in a 1 inch pipe. You will have to calculate the actual developed length.

    Engineers will typically take whatever developed length they calculate and add 50% to that number to compensate for fittings, valves etc.

    You should be able to find these pressure drop charts on line for the tubing of your choice.

    The pressure drop of one in floor circuit is added to the total pressure drop of the supply and return circuits. The GPM is the total required flow of all circuits combined.

    So your pump size will be based on the above factors, and will be expressed as X feet of head at 12.5 GPM.

    If you want to mess with wood as your heat source, don't forget what might happen in the event of a power failure, and consider installing a large buffer tank that will allow you to run the stove at a high rate of fire, which burns quickly and cleanly and stores the energy in the buffer tank. And as others have advised, consider treating the floor loops as a pressurized closed loop system.

    Good luck in your ventures.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
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