Gypcrete Delta T

Josh_10

I was hoping some of you could give me your opinions on proper Delta T for 1 1/2" gypcrete staple down radiant. I have been getting conflicting thoughts from the tubing manufacturers.

Aidan (UK)

delta T

The delta T when combined with the flow rate indicates how much heat energy was dispersed - it doesn't mean it went where you wanted it to go. You need to provide proper supply temps and adequate insulation below the floor to heat the room properly.

The typical standard for residential applications is 20F. With a 1gpm flow rate, a 20F delta T will deliver 10,000 btu's of heat.

A lower dT will have the floor heat faster and put out a more uniform heat disbursement, because the water is moving faster and has a higher average temperature. Designing this way may require shorter loop length and a higher head circulator.

(depending on the manufacturer, they may like the shorter loop lengths because that might mean an extra port or so on the manifold - more sales $$)

You don't say what the floor covering and tube spacing is, but I wouldn't suggest designing around a dT over 20F. This can lead to striping - a condition where it is easy to detect the position of the pex due to surface temperature differences.

Sometimes, we may design for a higher dT so that we can use a lower flow rate but still deliver the same amount of heat, or to cause return temperatures to be very low for condensing boiler applications. See the attachment. It will let you see very quickly the relationship between btu loads and flow rates.

I don't believe there is any "correct delta t for gypcrete". Its just 1 of many variable design parameters. Let's see if there are other opinions.

Hope this helped you.