Radiant heating is a popular and highly recommended method to heat a concrete slab. RADIANTMAX radiant heating systems use ½ inch BPEX radiant tubing with a spacing of 12” on center, with a maximum 300 foot loop length.
Why do we use ½” BPEX for Concrete Slab Systems?
A concrete slab is a great conductor of heat energy, and therefore an important thermal mass for radiant heating. Concrete slabs efficiently store heat energy and release it slowly over time. Since a concrete slab is efficient at storing heat, a 12” spacing is optimal, and anything closer is unnecessary.
Thermal mass also dictates the required tubing diameter. ½” BPEX is recommended to heat a concrete slab with low temperature radiant heating. Since concrete has a limit of the heat it can absorb in a given time, a larger diameter tube will not provide any benefits.
Solar Gain Affects Radiant Tubing Diameter and PEX Spacing
½ inch BPEX is used for indoor concrete slab radiant systems. Snowmelt radiant systems use ½ inch BPEX with a 6” spacing to accommodate for the high heat loss. All homes have 
some passive solar capabilities, and this is taken into consideration with the specification of ½ BPEX spaced 12” on center.
Different types of construction will allow for greater solar gain. The best type of construction to maximize solar gain is Insulated Concrete Form (ICF) construction. Eagle Mountain’s Center for Green Technology is build with ICF construction and benefits from significant passive solar gain during winter months.
The thermal mass properties of concrete offer benefits when used in all building components. ICF walls absorb heat during the day and release it slowly throughout cold nights. Concrete slabs retain heat for a longer period of time than any other material.
Reasons to Avoid Large Diameter Radiant Tubing
Large diameter radiant tubing requires a more powerful circulator in order to achieve the turbulent flow required for efficient heat transfer. Bigger is NOT better when specifying tubing for a radiant heating system. A larger circulator will increase the size and cost of your radiant system, without quantifiable benefits.
Concrete Slab Radiant Heating — 1/2″ BPEX 12″ Spacing
RADIANTMAX concrete slab systems use ½” BPEX with 12” spacing and are available as turn-key radiant slab packages for DIY installers. Eagle Mountain supplies Insul-Tarp concrete slab insulation as part of its RADIANTMAX radiant heating systems.
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