Hi all, (Climate Zone 6B)

We recently completed a high-end renovation in Madison, Wisconsin, that included a radiant floor heating system powered by an IBC boiler. We’re experiencing a persistent problem: the alcove area consistently remains 10°F colder than the adjacent kitchen during the winter, despite both spaces being part of the same zone and having identical tile flooring.

However, the two areas differ in how the radiant heat is delivered:

• The alcove utilizes piping embedded directly into the concrete.
• The kitchen uses an aluminum heat transfer layer above the slab.

The builder claims that this temperature variation is “within acceptable range” and not a defect, citing the absence of an explicit performance standard in our contract.

We’re seeking input from HVAC professionals, radiant design experts, and others with experience:

Is a 10°F ambient temperature difference in a radiant slab system between adjacent spaces common or acceptable?

Some additional details:

• We engaged an independent HVAC firm that suspects a design flaw, but they’re reluctant to confirm without access to the system drawings, which the original installer refuses to release.
• Floor sensors are present, but their exact locations are unknown due to the limited documentation available.
• On our first night in the house (in December), the interior was uncomfortably cold and required backup heating. The next day, the installer switched the Aube TH114-AF-024T thermostats to “floor-sensing only” mode, disabling ambient sensing. This did not resolve the problem, and they have not returned since.
• To keep the kitchen comfortable during winter, we’ve had to set the floor thermostat to around 78°F. Despite this, the adjacent alcove remains 8–10°F cooler daily.

We are trying to determine whether this persistent differential reflects a design flaw, particularly given that the alcove and kitchen are thermally distinct and yet share the same zone and thermostat.

Have others encountered this issue in slab-based radiant systems?