Thermostat and distance between Pex

[Rickcnc]

Looking at putting pex in my 28X40 shop 12 foot walls. One supplier recommends the pex be a 9" centers (6 runs), another says 12" is fine (4 runs).

Floor will be insulated to R10, walls R20, one large door 12X10 R16 one man door, no windows (6" slab)

Do I go with 9" or 12"

Second question should use a thermostat that measures slab temperature or air.. or both

 

[BadgerBoilerMN]

The closer the PEX tube spacing, the greater the "potential" output. Narrow tube spacing will also lower the required water temperature. If you have a condensing boiler, geothermal heat pump or any more conventional boiler with weather sensitive controls 9" may be a good thing. But I doubt it.

When I perform a heat load for a radiant floor the program kicks out a design water temperature. If I want a lower one, I tighten up the tube. This is another good reason to insist on a heat load before buying the first role of PEX.

On the other hand, they might be trying to sell more pipe...

As for thermostats; ambient air only will serve nearly every radiant floor I ever designed. There is a place for a floor sensor or even a combination, but I have rarely used them nor found a good argument for their regular use, save by the people who make or sell them.

Stick with the guys who provide a heat load upfront and the design to back up their claims. If the argument is good and the math correct, there is no such thing as too much tubing.

 

[Highbeam]

The most common, and traditional spacing for 1/2" pex is 12" O.C.

Most folks use an air thermostat. I put a spare tube in with a capped end in case I ever wanted to measure slab temp. Can't hurt to throw the tube in there.

I've never seen the benefit of doing a heat load calc until you start considering the boiler size. The default 12" spacing and standard rules work fine for the folks on this site and others that have done it in their garages. Then again, I'm not trying to sell the calc either so I have nothing to gain.

 

[pseudorealityx]

The most common, and traditional spacing for 1/2" pex is 12" O.C.

Most folks use an air thermostat. I put a spare tube in with a capped end in case I ever wanted to measure slab temp. Can't hurt to throw the tube in there.

I've never seen the benefit of doing a heat load calc until you start considering the boiler size. The default 12" spacing and standard rules work fine for the folks on this site and others that have done it in their garages. Then again, I'm not trying to sell the calc either so I have nothing to gain.

How do you determine the size of the boiler if you haven't done any load calculations?

 

[Highbeam]

At the time of boiler sizing a heat load calc is the very best tool.

 

[BadgerBoilerMN]

And always the 1st step for professionals, be they in the trades or engineering.

There is clearly no advantage to performing a heat load after the fact.