Warmboard-R Install Guide

Assembly instructions for retrofit radiant panels

Warmboard-R Panel Description

Warmboard-R is a hydronic radiant panel made from oriented strand board (OSB) with a conductive .025″ thick 1070 aluminum alloy skin bonded to the entire top surface. Each panel type is stamped with a series of aluminum channels on the top surface to hold 1/2″ PEX or PEX-AL-PEX tubing.

Warmboard-R consists of two panel types which weigh approximately 25 pounds, are 13/16″ thick and measure 23 7/8″ x 48″. In a completed assembly, Warmboard-R weighs 3.2lbs per square foot, which includes the panel, tubing and water.

Warmboard-R is typically installed over concrete or subfloor, though is also used in walls and ceilings. Non-aluminum filler panels are also available.

panel type detail

Installation Highlights

  1. Count your panels when they arrive on site and confirm the shipment is correct. If there are any questions or inconsistencies with your plan set, call us immediately.
  2. The existing subfloor should be reasonably smooth and flat prior to the installation of Warmboard-R. Inspect for squeaks and refasten to joists if necessary.
  3. Warmboard-R and the subfloor MUST be dry prior to installation. Warmboard-R CANNOT be exposed to rain before or after installation. 
  4. Gap 1/8″ between panels on the 4′ side and always use the alignment pins when fastening to ensure
    the tubing paths between panels line up.
  5. ONLY use tubing approved by Warmboard, Inc. DO NOT use silicone or other types of adhesives in the tubing channel.
  6. Tubing layouts for Warmboard-R can be quite flexible. Make field revisions as needed but DO NOT exceed 275 linear feet per loop.
  7. Custom routes require a router with a minimum 1.75 horsepower (2.25hp is recommended). DO NOT attempt a custom route without the proper template guide.
  8. When Warmboard is installed over a crawl space or existing subfloor, a minimum of R-19 insulation
    is required beneath the panels to prevent downward heat loss.
  9. Review the installation manual before installing finish floors.
  10. The surface temperature of finished floors is not to exceed 85ºF. This rule applies to the entire radiant industry, and is endorsed by the Radiant Professionals Alliance (RPA) and International Association of Plumbing and Mechanical Officials (IAPMO).
  • Warmboard-R panels are but one component in a complete radiant system. System design should be done in accordance with Radiant Professionals Alliance (RPA) guidelines, manufacturers’ recommendations for ancillary components, and is the responsibility of the system designer.
  • By reading these highlights before proceeding, you will save you time, money and hassle.
  • Warmboard products are required to be installed. and managed by experienced and licensed trade professionals pursuant to current local laws. Failure to use proper installers will void any product warranty.

Approved Tubing

PEX Aluminum PEX tubing, 1/2″ ID

  • Warmboard PEX: PEX-AL-PEX
  • Bluefin: PEX-AL-PEX
  • Mr. Pex: PEX-AL-PEX
  • Watts: PEX-AL-PEX


ONLY use the supplied Warmboard PEX-AL-PEX, which has been specified and tested by Warmboard for use with the WCS. 


PEX tubing, 1/2″ ID

pex tubing

  • HeatLink FL PEX-a
  • Mr. Pex
  • Rehau Raupex Oxygen Barrier
  • Uponor helioPEX X2
  • Uponor/Wirsbo hePEX
  • ViegaPEX Barrier
WCS tubing

Although Warmboard approves these tubing products for panel projects, they are NOT supported for use with the Warmboard Comfort System. ONLY use the supplied Warmboard PEX-AL-PEX.

Necessary Tools

Tools and Materials

  • Circular saw, carbide blade
  • Router, minimum 1.75 horsepower, 25hp recommended
  • Electrician nailing plates
  • 16oz Rubber mallet
  • Warmboard approved tubing
  • Shop vacuum
  • Drill motor with a 3/4″ drill bit
  • PEX tubing cutter
  • Wax pencil or permanent marker
  • Tubing un-coiler
  • 4″ Grinder or Dremel tool

Warmboard Installation Kit Content

(supplied with each order)

  • Warmboard panel/tubing plans
  • 3 Custom routing templates (wood)
  • 5/8″ Router bit
  • 2 Alignment pins
  • Router template guide
  • Router guide lock nut

Installing over Subfloor

Preparation for subfloor installation

It is essential that the existing subfloor is both flat and smooth before the installation of Warmboard.  Inspect the subfloor for evenness along the joists and flatness between the joists.

If necessary, sand the subfloor and install extra blocking below. Inspect for squeaks and refasten with decking screws as necessary.

Cutting and installing Warmboard-R is very straightforward. The panels can be trimmed with a standard skill or table saw and will rip just like ordinary OSB. We recommend cutting with the aluminum side down to help avoid burrs.

Method 1: Screw Only

Use a #8 x 11/2″ GRK R4 Multi-Purpose screw (or equivalent) with a top 1/2″ smooth shank. Fasten with a pattern of 3 rows of 4.

  • No pre-drilling required
  • Self-counter sinking
  • No adhesive needed

Method 2: Nail and Glue

Use a construction adhesive designed for bonding OSB to plywood (Loctite PL Wood Adhesive or equivalent). Follow all directions specified by the adhesive manufacturer.

For nailing, use a ring shank or a screw nail. To determine the appropriate length of the nail to use, evaluate existing thickness of subfloor and add 13/16″. Fasten nails with a pattern of 3 rows of 4.

panel over subfloor

  • Warmboard-R and the subfloor MUST be completely dry, with a moisture reading between 8-12% before, during and after installation.
  • DO NOT expose Warmboard-R to rain before or after installation.
  • It is crucial to use the alignment pins to line up the channels from panel to panel.
  • Cut panels with the aluminum side down.

Installing over Slab

Benefits of installing over Concrete slab

Installing Warmboard-R over a concrete slab can retrofit a basement, home remodel or new home with a state of the art radiant floor heating system.

A broad range of finish floor options are available, including hardwood, tile, carpet, vinyl and linoleum.

Concrete Slab Requirements

The existing slab MUST be level and flat. A newly poured slab needs to be well-cured for a minimum of 30 days, and a moisture test should be conducted to ensure the slab is properly cured prior to installation of Warmboard-R.

Like any wood product, if Warmboard-R panels are exposed to standing water or moisture intrusion, the wood will swell and rot. DO NOT use Warmboard-R if these environmental conditions are possible during or after construction.

Testing for Moisture

There are several methods by which to test the moisture content of a newly poured slab, the simplest being the “Plastic Sheet Method” (ASTM D 4263-83).

To do this, place an 18″ x 18″ clear plastic sheet on the slab and tape down on all sides. DO NOT allow the sheet to come in contact with direct sunlight or excessive heat. After 16 hours, if any condensation is found on the underside of the plastic, or if the slab surface is darkened, the concrete is too wet for a coating application.

NOTE: It is possible for this method to yield a false result in cooler conditions when the concrete may retain moisture and fail to condense on the plastic.

To ensure a reliable result, make sure that the surface temperatures and ambient conditions during the test are very similar to those present after the Warmboard panels are installed.

If not performing a moisture test, we recommend giving a newly poured slab 90 days to cure fully. Once certain of the moisture level of the slab, we recommend one of two installation methods.

  • The slab MUST have sufficient drainage from rain and snow at all times. Failure to provide sufficient drainage will void any product warranty.
  • Warmboard-R MUST be mechanically fastened, not just floated or glued. Failure to mechanically fasten the product will void any product warranty

panel over slab

Method 1: Fasten Directly

Apply either a liquid vapor barrier or a 6- or 10-mil polyethylene vapor retarder overlapping two feet (2′) at the seams. Continue with Warmboard-R panel installation using split drive anchors, Tapcon concrete fasteners or powder-actuated fasteners.
We recommend a maximum of 9 fasteners for each

Method 2: Using Insulation

Install a 6- or 10-mil polyethylene vapor retarder directly to the slab, overlapping two feet (2′) at the seams. Next, install a 1/2″ Homasote Comfort Base or Homasote 440 SoundBarrier over the entire slab (adding a R-value of 1.2). Gap all Homasote panels 3/16″ from all adjoining panels and 3/8″ from walls.
Use fasteners (21 per panel) to attach the entire assembly to the slab. Find the instructions for these products at homasote.com

Fastening to Concrete

Concrete drilling should be done with the Warmboard panels in place (pre-drilling the concrete is not recommended). Use a heavy duty roto hammer drill and a high-quality masonry drill bit. The hole should be 1/2″ deeper than the required specification.

Once drilled, draw the drill bit in and out a few times to loosen excess material. Use a shop vacuum to remove the debris.

Choose one of the following methods to fasten the Warmboard panels to the concrete. Use a pattern of 3 rows of 3.

  • Flat head Split Drive Anchors will save you many hours of labor, but may be difficult to find in retail locations. Call 888.498.5747 or visit confast.com.
  • Fasteners MUST exceed a length of 2 1/4″ if using Homasote between the slab and Warmboard-R.