Gypsum Concrete

A method going back decades, but a lot has changed in 50 years

For decades, high mass radiant heating had been the default method for radiant heating. But it has many, many drawbacks. Below is a comparative look at both gypsum concrete and Warmboard.

Performance

This video shows a side-by-side comparison of the two systems. Both products experience the same air temperature of 65ºF (18.3ºC), the same water temperature of 120ºF (49ºC), and the same flow rates. And yet, with 12 inch tubing spacing, Warmboard is able to produce 10 BTUs of heat in 20 minutes, while it takes gypsum concrete 2.5 hours to reach the same output. Later, Warmboard is generating 20 BTUs/hr/sf (British Thermal Units, per hour, per square foot) while the other system is only outputting 12. This clearly shows that Warmboard is far faster in its response and energy usage.

The striping (the temperature variation across the panel) only varies by 2.4ºF on Warmboard while the gypsum concrete is 5.9ºF. While temperatures variations below 3º are indistinguishable to the touch, a 6º variance will be felt as you walk across your floor.

By doubling the amount of tubing, gypsum concrete has a much better response time. And yet, it still does not perform as well as Warmboard. Here, Warmboard again reaches a 10 BTU output in 20 minutes, while gypsum concrete takes an hour. Striping is below the threshold for Warmboard, and just above for gypsum concrete.

Typically, Warmboard uses water between 80-110ºF, while gypsum concrete uses 140ºF water. That not only means lower energy bills for Warmboard owners, but it allows condensing water heaters to run more efficiently and for easier interfacing with solar and geothermal technologies. Low water temperatures also extend the life of your heating equipment.

Note: Temperatures were taken from just above the center of each panel. Striping differences were also gathered from this area. Temperatures from on top of the tube were compared to temperatures at the midpoint between the tubing pattern.

Installation

Gypsum concrete weighs 15 lbs per square foot dry (25 lbs wet). Because of this, structural changes must be engineered to accommodate the weight, including code enforcement and seismic considerations for certain parts of the country. Gypsum concrete takes many days to dry, and can lead to potential mold issues if not dried adequately.

Because gypsum concrete is a poor conductor of heat, installers often double or triple the amount of tubing in order to improve output. While this does improve response times (as seen above), it also increases the amount of tubing required, the number of manifolds and the complexity of the control system - not to mention the additional labor.

For those installing hardwood, high mass systems will also require sleepers (not used in our videos). Sleepers are wooden 2x4s located every 12 inches within the concrete pour which allow the hardwood to be nailed down properly. These 2x4s break up the cement space and interrupt the transfer of heat across the surface. The result is much higher striping and much more noticeable temperature differences. And hardwood installation becomes extremely problematic and expensive. Sleepers are warped as the concrete dries creating an uneven surface to install the flooring. Increased striping can age the floor unevenly, causing warps and cracks. In stark contrast is Warmboard, which avoids all these hassles while simplifying the install process. Another option is to one to two layers of plywood over the surface of the dried concrete. This eliminates the sleepers, but also dramatically inhibits heat transfer by adding over an inch of material between the heat source and the interior space.

Summary

The nature of gypsum concrete limits flooring options. Hardwood can be extremely difficult (and expensive) to install, while thick wool carpets can actually prevent the heat from entering the room. With Warmboard, your flooring choices are not limited.

Response times with gypsum concrete are very slow, taking hours to adjust up or down slightly. In some places, this contributes to even more discomfort. Should the weather change rapidly, high mass systems can’t keep up. The heat will come hours after you need it, and then your home will be too hot when the weather warms up again. In fact, some modern thermostats have a "radiant mode" which attempts to overcome this slow response by guessing the heat output you will need 3 hours in advance. But even with all of our modern technology, weather is unpredictable and can change quickly.

Warmboard will also work with thermostat features like nighttime setback. This features allows the temperature of your home to drop several degrees while you sleep. But gypsum concrete responds to slowly to benefit from this feature.

Choose the modern alternative based on science and sound construction principles. Choose Warmboard.