Radiant Floor Heat

CG

Does anybody have accurate information on which size tubing is best for under floor heat? I am getting mixed responses from suppliers. Some say to put 1/2" tubing 8" OC, others say you can use about half as much tubing if you use 3/4". All the engineering data seem to support this. Does anyone have knowlege on this?

Alan(CaliforniaRadiant)Forbes

Tube size

doesn't get you more heat; it just increases the allowable loop length.

As far as the engineering data to support this, I'll leave that to others that follow.

Best wishes,

Alan

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Rick Kelly

underfloor radiant

Ease of installation is something to consider. 1/2" tubing is going to be easier to work than 5/8" or 3/4". Bending radius is a huge factor. Using 1/2" is the only way to achieve consistant spacing and loop ends. Larger sizes will at least require oversize loop ends. Hole size is another thing to consider. I drill 1 3/8" holes for 1/2" and that allows a nice margin of slop to make pulling reasonable. Any reasonable size job could involve hundreds of holes. How big are you going to make those holes? Bigger holes usually mean more effort.

Use 1/2" and keep your loop lengths below 300' total and you might never know how unhappy you could have been.

Mike T., Swampeast MO

You seem to be asking...

...if ¾" tube 16" on-center will give the same output as ½" 8" on-center.

NO!

Regardless of how heat is leaving the tube; be it embedded, stapled, suspended or conduction enhanced, THE HEAT TRANSFER IS A FUNCTION OF THE AREA OF THE TUBE.

½" tube has about 23½ square inches of surface area per foot.

¾" tube has about 33¾ square inches of surface area per foot.

Instead of 2 times the surface area of ½" tube, you get 1.33333333333333 times.

While you CAN "play" with things SLIGHTLY by changing velocity and restriction (thus delta-t and delta-p) you WON'T be able to to make up for this difference with ANY acceptable velocity or tube length!

Dave H_2

It's not size that matters

when looking at floor heating!

You have to remeber that the tubing is not heating your house, but the flooring system. The tubing just delivers the heat to the floor.

Also, another thing to remember about radiant floor heating, you want to heat the space slowly and gently, never blast the area with heat, it will be the most uncomfortable room of the house if operated in this fashion.

If you have a large diameter tubing and 1/2 the amount, you need to deliver the heat faster which will result in a myriad of difficulties; flywheel effect of the air and floor temp, striping of the floor (hot and cold spots).

Remember that you DO NOT want a radiant heating system, you want a warm floor, the radiant heating ends up being a by-product.

Radiant heating is acheived by slowly extracting the heat out of the floor, not out of the tubing. Larger diameter can deliver more, but we don't want to deliver it that fast. Typical flow rates through radiant tubing is in the range of 0.3-0.8 gallons per minute. Safe flow rates for 3/4" is 4 gallons per minute. So working with 1/2" or even 3/8" diamter tubing is well within design limitations and as Rick stated, so much easier to work with!!

Dave H.
If your floor is not comfortable, you are not comfortable

Boilerpro_3

How bout 3/8 inch....

Much easier to use and fits the needs of most residential applications. Tube spacing is the primary factor affecting heat output.

Boilerpro