Notes from on installation of a radiant floor system. Notes are particular to water systems going under existing wood subfloors with a tile finish.




a.       Use water and not antifreeze unless there is a freezing issue. (pg 42)

b.      Water temperature going into the tubes: 110° to

c.       120° for concrete, 130° to 140° to for staple up, 110° for Gypcrete. (pg 71)

d.      The heating loops can be up to 500 ft long. (pg 4)

e.       ½” radiant loop normally flows at less than 1 gpm. (pg 4)

f.        Use 1/8” air gap between bottom of subfloor and pex. (pg 4)

g.       Install extra tubing for high heat loss such as glass wall or door at end joist and ends of runs. (pg 27)

h.       Do not place tubing within 12” of exterior slab edge. (pg 7)

i.         Do not install tubing under toilet; it could melt the wax ring. (pg 7)

j.        If you take 500 times the number of rolls of tubing designated for this floor and divide that by the length of the joist space, this will give you the number of single runs you can install. If the number of single runs exceeds the number of spaces, this number represents the number of doubles you can run. Be sure to allow extra for the run to the manifold. (pg 55)

k.      Designing a radiant system with all of the loops the same length eliminates the balancing problems and the equipment associated with it. (pg 58)

2.      PEX TUBING

a.       ¾” pex staple from Peter Mangone Inc. on ½” pex, on 8” centers (or 16” to 24” centers (pg 18)). (pg 4). Use hand operated staple gun. (pg 18)

b.      Pex-A and Pex-B are both acceptable. (pg 7)

c.       Pex-A is slightly more flexible. (pg 7)

d.      Pex-B is more uniform in wall thickness and will outperform Pex-A in freezing and temperature performance. (pg 7)

e.       Pex-Al-Pex sometimes is not Pex. (pg 51)

f.        Do not use Pex-C. (pg 51)

g.       Pex tube should pass ASTM F876/F877 (SDR 9) certificate as tested by NSF (14 & 61) and CSA, conform to International Standard 9001, and have a 25 year warranty that includes property damage. (pg 51)

h.       Ultraviolet light will cause accelerated aging on pex. Do not expose  (pg 7)

i.         The Pex-A made by Safelink is the best, more flexible and stronger than others. (pg 67)


a.       Setback thermostats do not save energy. (pg 4)

b.      Place the thermostat so that it will heat up from this solar gain and respond quickly. In other areas place the thermostat between 4 ½ to 5 foot high, on the inside walls, and away outside doors and heat sources. (pg 19)


a.      Do not use emission plates or aluminum foil sandwiched between subfloor and floor. (pg 3, 4)

b.       Install insulation on exterior rim of joist (pg 7)

c.      Radiant barrier: double bubble with a layer of aluminum foil on both sides. (pg 22)

d.       2” high density foam is the best insulation available for sealing the rim joist. FDBF, High-Rad (pg 22)

e.        Each inch of dead air space between the foil and the tubing is worth an R-3. (pg 22)

f.       Never put foil next to tubing. (pg 23)

g.       Areas with vaulted ceilings above will need a layer fiber glass. (pg 24)

h.         Crawlspaces will need fiberglass plus radiant barrier under the joists. (pg 24)

5.      BOILER

a.       Modulating/condensing boilers. (pg 4)

b.      Designing a radiant heating system with a combo-unit is much easier than with a boiler. Designing a radiant system with a combo-heater allows you to run the water in the system at the same temperature as the tank, this eliminates the need of mixing valves and extra pumps. (pg 58)

c.       Do not design the system around the pump that is furnished with the boiler. (pg 58)

d.      Come out of the boiler with 1 ½” or 1 ¼” black pipe directly into the pump flange. Then come out of the pump with a 1” pump flange and 1” copper. There is no need for a shutoff on each side of the pump. You should nto put any crossover pipes between the manifolds, You should put a full flow ball valve on each zone. (pg 44)

e.       There is no need to install temperature gauges in addition to the gauge that comes with the boiler. (pg 44)

f.        Flow meters are unnecessary in a residential heating system. Every system should be design with ball valves on every loop for balancing. (pg 44)

g.       Be certain to use a boiler drain verses other types of valves on the return side. (pg 44)

h.       You should use an all brass fill valve. (pg 44)

i.         Boiler pressure should be 12-15 lbs when cold and 15-22 lbs when hot. (pg 44)

j.        A ball valve should be installed in front of the fill valve.  Fittings should be copper or brass. (pg 44)

k.      The gate valve is used for purging and to service the zone valves and should be 1 ½” or 1 ¼” to match the iron pipe coming out of the boiler. This is a good place to change to copper with a 1” brass reducing busing. (pg 44)

l.         The purge valve should be a ½” boiler drain valve. It is the only purge valve you need. All systems should be self purging, but this valve makes it faster and more positive. (pg 44)


a.       Need no more than the smallest expansion tank. Expansion tank is made out of steel and should be screwed into a copper fitting. (pg 45)

b.      The pipe fitting must be on the top of the expansion tank. (pg 45)

c.       Do not place the expansion tank to close to the pump. (pg 45)

d.      Install the zone valves on the return manifold. (pg 45)

e.       Float vents should be cast brass. This is the only vent needed on a radiant system. (pg 45)

f.        The pressure relief valve on top of the boiler or as close to the top of the boiler and the feed water must be on the bottom. (pg 45)


a.       By using a higher head pump you can keep all of the plumbing in the mechanical area, this reduces the cost and the chance of damage by a leak. (pg 58)

b.      Adding pressure regulating bypass valve you can design a system using one pump. (pg 8 )

c.       The new cartridge and sealed pumps are very well suited to these higher head requirements. (pg 46)

d.      When the pump moves water upward, the air moves freely though it, and the heat from the motor is carried away by the water. (pg 46)

e.       Steel and copper creates a dielectric union. Copper has no problem with brass or cast iron. Put a brass or cast iron fitting between the steel and the copper. (pg 46)