Installing Tubing Between Floor Joists


Installing radiant heat between the floor joists is a very effective way to get heat into any space. This is also known as the “staple-up radiant heating” application. As long as you can see the floor joists from below then you can add radiant heat. This application works well in new construction and is also a very popular retrofit option.

In our opinion, a staple-up radiant heating system must be installed correctly in order to be efficient and effective. Again it is our opinion that the following steps must be taken for a staple-up installation to work effectively:

Install Aluminum Heat Emission Fins (aluminum plates)

Many debate the merit of installing plates. Some say they’re noisy (ours are not). Others say they’re too difficult to install. Some say they aren’t necessary. If people tell you this they are trying to sell you a system simply on price and don’t care how well it works or how efficient it is. We have nearly 40 years of experience in this business. The installation of aluminum plates is CRITICAL. They will allow you to run cooler water temps through the radiant tubing. Lower water temps=lower operational cost. Installing the plates will also allow the floor to warm up quicker which again will equate to lower operational costs. Finally, the aluminum plates allow for more even and equal heating across the floor surface. You’ll be less likely to feel warm and cold spots.

Install Aluminum Reflective Barrier

About 1-2″ below the radiant tubing and plates, you should install an aluminum reflective barrier. This is nothing more than a craft paper with an aluminum facing. It has fibers that run through it so it doesn’t rip or tear but it can be cut with a pair of scissors. The reflective barrier comes on a roll that is 50″ wide and must be cut so that it can fit between the joists. We have an installation video that shows how to do this.

The purpose of the reflective barrier installation is to reflect the radiant heat waves back up towards the sub-floor. We are also trying to create a small dead air pocket that further helps to equalize the heat transfer. Some will argue that the reflective barrier isn’t necessary and that it will become covered up with dust and lose its effectiveness over the years. We still feel it’s an important piece and since it’s relatively inexpensive, it should be installed.

Install Insulation 

Many people ask us if it’s necessary to also install insulation below the radiant tubing, heat transfer plates, and reflective barrier. If you can only do this once because the ceiling will be finished then the answer is absolutely yes. The amount of insulation is dependent on what is above and below. If there is carpeting or a high heat loss area above then you should put in R-19. If not, you can probably get away with R-13 but R-19 is better. The type of insulation doesn’t really matter all that much.

If there is an unheated basement below then you should use R-19. Most people don’t mind if they lose a little bit of heat downward in this scenario. If the heat loss downward is entirely wasted to a crawl space, for example, then your insulation method should be extensive. You should try to get in a minimum of R-30. Some will insulate between the joists with fiberglass and then seal the entire underside with rigid foam.

If the ceiling will not be finished, some will wait and see how the system performs and then add the insulation after if necessary. What can happen if you don’t insulate? Since radiant heat will go in all directions, the heat will just as easily go downward. The basement will get too warm and you won’t get enough heat into the space above.

Radiantec conducted our own plate study and you can find the results here: Plate Study Page


Radiantec Home Free Quotes! DIY Contact Us