When a homeowner upgraded his old boiler to a new, combi system that worked with his heat pumps, he noticed he couldn’t get his bathroom to warm up. With the idea to tap into his boiler’s water supply to install radiant floor heating in mind, the homeowner called the team at Ask This Old House for help, and Richard Trethewey answered. In this video, Richard helps him install a new radiant floor system in his retro bathroom.
How to Install Radiant Floor Heating
- Start by mounting the heat exchanger and manifold to the wall relatively close to the combi boiler. The close proximity will allow the heat exchanger to run as effectively as possible without the heating water cooling much.
- Connect the pump radiant floor pump and manifold. Use the solderless press machine for simple, strong connections. Make sure to have an inspector or certified plumber check the installation of pressure relief valves and check valves.
- Carefully trim and knock out the blocking between the joists using the oscillating tool and a hammer. It’s not necessary to remove the entire blocking board—just remove the top 2 inches or so, leaving enough clearance for the plate and the heating tubing.
- Install the transfer plates in sets of two rows per joist bay. This will allow the tubes to track down the joist bay and loop back before moving to the next bay.
- Drill holes in the joist bays to pass the PEX tubing through from bay to bay. Drill these holes close enough to the subfloor to keep them out of the way but low enough that the tubing will be safe from nails and screwdriving from the floor above in the event of a flooring change.
- Weave the PEX pipe through the joist bays and use a rubber mallet to strike the lines to clip them into place. Start on the section furthest away from the manifold and work backward.
- Reinstall any insulation that’s been removed.
- Connect the new radiant system at the manifold to operate the system. Use the compression fittings included with the manifold to attach the PEX piping. If there are additional zones not being used, consider using a small length of pipe (known as a jumper) to close the loop.
- Connect the new system back to the water heater using the solderless connection tool. Be sure to include shut-off valves to make the system serviceable.
Note: Be sure to have your system inspected by a local plumbing inspector or contractor to ensure all of the proper safety devices are installed, including pressure relief valves, fill valves, expansion tanks, and other devices not mentioned above.
Materials
- T-fittings (solderless)
- Compression connections
- Push-to-connect fittings
- Transfer plates
- PEX pipe
- A heat exchanger with pumps
- Screws
- A variety of check valves
- Pressure relief valves
- Expansion tank
- Fiberglass insulation
- Propress for solderless connection
Tools
Tools & Materials
Resources
Richard mounts the heat exchanger by securing it with screws. Then, using a pipe cutter, he cuts to allow room for a T-fitting. Richard uses compression connections and push-to-connect fittings to run the piping from the T-fitting supply and return of the heat exchanger.
Richard mounts the manifold by securing it to the plywood with screws. He then uses a pipe cutter to cut and connect the piping from the supply and return of the heat exchanger into the supply and return lines on the manifold.
Richard mounts the radiant heat transfer plates to the underside of the subfloor using screws. The homeowner snaps the PEX piping into the mounted channel plates up and down the joists for the length of the room and then packs fiberglass insulation on top of the piping to ensure that all the heat generated by the radiant goes up towards the bathroom.