Retrofitting Hydronic Heating into an uninsulated Basement Slab

Concrete and Masonry, HVAC & Mechanicals, Insulation and Air Sealing, Kitchens and Baths

Retrofitting Hydronic Heating into an Uninsulated Basement Slab

Taken from: ProTrade Craft for Residential Construction Pros 05/23/2016

Retrofitting in-floor heat is a great way to warm up a chilly basement bathroom. But unless you have insulation under the heating system, your customers are going to spend fat stacks of Benjies heating the earth every month.

Step by step:A2A59FF6-CC30-48B7-B6E3-7B94C3D64AAE

To keep the heat where you want it, cut out the slab before installing the heating system. Dig deep enough to allow for gravel, insulation, and a slab on top. Cover the earth with compacted gravel to support the slab and keep water from wicking in. Reinforced plastic over the gravel stops water vapor.
Rigid insulation comes next surrounding the new slab on all five sides.

You will need some sort of steel reinforcement, either wire mesh or rebar and then install the hydronic tubing. Pour the slab over the tubing, let it cure, and cover the whole assembly with flooring—and be confident that your customers Benjies will stay in the bank.

2012: IECC:

2015 IECC:
Section 402: Building Thermal Envelope
R502.1.1.1: Building Thermal Envelope (existing building)
R 502.1.1.2 Heating and Cooling Systems (existing building)