- Q.My company has been
contracted to build a new bathroom. Plans include a
tile floor installed over a radiant-heated slab. Will
the heat generated by the hydronic tubing embedded in
the slab cause problems with the wax seal between the
toilet and the drain?
A.Mike Casey, a licensed
plumber in Connecticut and California and coauthor
of Code Check Plumbing, responds: Yes, both
electric and hydronic radiant systems can get hot
enough to melt wax, leading to failure of the
toilet's wax ring. While neither the IRC nor the
Uniform Plumbing Code specifically addresses this
issue, both do state that installation of radiant
systems should comply with manufacturers'
instructions. And every instruction manual I've
read notes that it's important to keep a heat
source — such as an electric heating mat
or hydronic tubing — 4 to 6 inches away
from the toilet-floor waste penetration. Some even
recommend insulating around the penetration to
further prevent heat transfer, particularly with
metal drain pipes.
A concerned installer could provide additional
insurance by using a neoprene ring in lieu of the
standard wax ring — but in my experience,
the neoprene rings tend not to seal as well as
To play it safe, keep the radiant pipes or
heating mat 6 inches away from the drain, stick
with the wax-type seal, and insulate only if the
drainpipe is metal.