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BTU's per linear foot of PEX

David CurryDavid Curry Member Posts: 8
Looking a Radiant project in an addition that has a lot of glass windows. Addition is 13x32 feet. The heat loss calcs say I need 16,000 btus/hr. I wondering if I need to space the tubing closer together than normal (2 tubes per 16") Planning on a staple up job using either 3/8" or 1/2" HePEX with aluminium plates.
Does anyone of the top of thier head know the rough BTU's per linear foot for this type of system


  • Brad WhiteBrad White Member Posts: 2,440
    I think

    you need to post more information, such as your target water temperature, floor coverings and the like. Too many variables.

    You are at over 38 BTU's per SF assuming that the floor area is 100% available for radiant.

    I would take the radiant as far as I could to maybe 25-30 BTUH per SF then supplement with panel radiators, personally.
  • David CurryDavid Curry Member Posts: 8

    Tile floor over 5/16" durock cement board over the 3/4" underlayment. Water temp 110-155 deg or so I think is about right.
    Looks from what you said I am right to be abit concerned.


  • no need to go any further brad, you hit it on the heat. Take the floor to 25-30 BTUs/h/sq ft, do the rest with supplemental.
  • ALHALH Member Posts: 1,790

    The limit is the allowable floor temperature. Somewhere around 30 btu/sf is all you can get without raising the floor temperature until it is uncomfortable or dropping the mean radiant temperature until it is uncomfortable. 155°F fluid temp with pex and extruded plates will provide floor temperatures that are much too warm for comfort.

    One option is to supplement with a radiant ceiling. Pex-Al-Pex and Thermofin-U makes a nice radiant ceiling panel.
  • David CurryDavid Curry Member Posts: 8
    Last piece of data

    Again thanks for the thoughts confirming some of my gut feelings.

    One more data point. Part of the room is going to be used as an aviary for large parrots. So one of the drivers for radiant was to eliminate the baseboard heating which would be really tough to keep clean.

    The radaint ceiling panels are interesting. Also thinking about a forced air cooling system and filtering. Anyone have any thoughts on adding supplemental heat in the forced air system.
  • MarsMars Member Posts: 65
    Hydronic heating coils

    You could add a hydronic heating coil to the air handler and use it as a secondary stage of heat and it should take care of the problem. The Honeywell Vision Pro 8000 thermostate can run two stages of heat but you would need a relay to controll 2nd stage.
  • kalkal Member Posts: 60
    i dont like all my eggs in one basket...

    so i dont like hydro air unless someone twists my arm (read - lots of mula-shmula) - with today’s pvc vented 90+ furnaces, there is no reason not to avail yourself of it unless it's already installed and you are adding a coil, and i get better temps at the unit to keep the moisture from the humidifier in suspension – and I don’t have to worry about freezing the heating coil if I have a fresh air intake in the winter – or the airflow restriction – and having yet another coil to clean in the long term, nor worry about heat migration from my manifold producing indirect hot water in the summertime – sure I put spring checks on both the supply/return to mitigate that – but you have to ask yourself why?, the new furnaces are smaller, quieter, and efficient - you will have a hard time convincing me, especially since my neck still hurts from the last coil repair job

    ps with today’s airborne pathogens, I really recommend an ultraviolet light treatment system in each air handler, I like to put the 2bulb Honeywell unit over the A-Coil
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