Existing concrete slab and Warmboard

Simply Rad

Hello all and thanks for input
First, I want to say this is not a discuss on the performance of the radiant panel but the heatloss. I have a project starting soon, with an existing home and large addition. We are converting the entire home to radiant floor hydronic. The builder has already spoken with Warmboard for the project. I am very familiar with WB and have over 100 homes with comfort system. At this point it not about the system but about the small details. The original home was built in 1987 without under slab insulation. In prior projects with this application I have used Roth panel, because of the built in insulation. The builder is looking to me for advise as I have expressed my concern about the downward heatloss of installing the WB directly on the slab. Radiant panels are about conduction heat and insulation. Radiant heat seeks cold no matter if its up, down left or right. The insulation is used to guide the radiant heat where its intended to provide comfort. I did a simple heat loss for the large recreation room, which sits on the existing slab. One calc I used R .75(7/8" thickness of the R panel) underslab insulation for the WB and the other with R 4.7 for the Roth panel. The difference for that room was 22,500BTU/hr for non insulated VS 13,500BTU/hr for Roth panel. That is just one room in the lower level and the calcs are just for one hour for heatloss. In my mind the Roth panel is the clear choice for energy savings. What do you think of this?
Jeffrey

hot_rod

Actually there is no much insulation under the tube itself with the Roth panels. Or the WB for that matter. So I'm not sure how they come up with the R-value numbers? Must be the thickness of the foam or plywood itself, not under the tube thickness?

But certainly the foam has an edge for R-value.

I do like the Roth with the 6" spacing option, which helps in high load areas to pack in extra tube. The foam provides a nice feel to any wood flooring used over it. It's very easy to cut and install also, compared to wood based dry systems.

It is hard to put an exact number on downward loss under an uninsulated slab. Soil type, moisture content, depth of slab, local frost levels, etc.

I like the Roth for over slab applications.

Simply Rad

HR
I used Uponor design suites heatloss program. For the WB I used .75R for the 3/4" wood and 4.7R for the claimed Roth panel R value. For the program I have the option of slab on grade or below grade(and how deep below grade), there's an option for water table underslab. So a lot of the questions you asked are addressed with the Design Suites program. Also, for underslab insulation you can chose edge, perimeter and slab insulation. So I feel the downward loss is addressed relatively accurate. Anyway, the only variable I changed in the heatloss comparison was the R values of the WB and Roth. This is the best comparison for downward heatloss I can come up with. I am going to suggest the Roth Panel as clearly some insulation is better than non.

Sal Santamaura

If ceiling height isn't an issue, can't one use rigid insulation under the Warmboard? Honest question; I have no idea.