Super cozy radiant heat

Radiant heat is scientifically proven to be healthier and often significantly cheaper to operate than convective forced-air systems. It eliminates the ductwork losses and air turbulence that drive up utility bills and circulate allergens. [1, 2]

Why Radiant is Healthier

• No Allergen Circulation: Because it does not use forced air, radiant heat does not blow dust, dander, pollen, or mold spores around your living space.

• No Respiratory Dryness: Convective systems inherently dry out the air as it passes over heating elements, which can irritate sinuses and throats. Radiant heating warms objects, maintaining natural humidity levels.

• Physiological Comfort: Radiant heat warms your body and surfaces directly (just like the sun), allowing you to feel comfortable at lower air temperatures. 

Why Radiant is Cheaper to Operate

• No Duct Losses: Traditional forced-air systems lose 20% to 30% of their thermal energy through leaks and uninsulated ductwork. Radiant systems avoid this entirely.

• Reduced Stratification: Convection heats the air, which immediately rises to the ceiling where it is not needed. Radiant heat targets the floor or wall zones where people actually are.

• Lower Thermostat Settings: Because the surrounding surfaces and your body are warmed directly, you can keep your thermostat set roughly \(2\) to \(4\) degrees lower without sacrificing comfort. Every degree lowered can save around \(6\%\) in heating costs. 

High mass radiant heat drastically outperforms convection heat for heat retention. Radiant systems heat solid objects (floors, walls, furniture) directly, which store and slowly radiate warmth back into the space. Convection simply heats the air, which is highly inefficient for retaining heat because warm air is easily lost to drafts and poor insulation. 

Key Differences in Heat Retention

• Heat Storage (Mass vs. Air):

  • High Mass Radiant Heat: Solids have high thermal density. A masonry heater or a concrete radiant floor slab absorbs and retains significant thermal energy for hours, releasing it steadily even after the heat source is turned off.

  • Convection Heat: Air has low mass and very poor heat retention. Once the heating element (like a baseboard heater or furnace) stops, the hot air rapidly dissipates, cools, and requires constant reheating.

• Drafts and Infiltration:

  • High Mass Radiant Heat: Because it transfers heat via invisible light waves directly to objects, it does not rely on air circulation. Heat is not easily pulled out of the space by drafts or open doors.

  • Convection Heat: Relies on air continuously rising and falling. If a window or door opens, the warm air escapes immediately, often forcing the system into continuous, inefficient operation.

• Temperature Distribution:

  • High Mass Radiant Heat: Warms the floor and objects first, ensuring consistent, 360-degree comfort where people are.

  • Convection Heat: Leads to stratification where the hottest air collects near the ceiling, wasting energy where it's not needed while leaving the floor cold.

Radiant heat directly warms your skin and objects via infrared waves instead of heating the air. Because it bypasses the air, it generally feels about 4°F (or $\sim$2°C) warmer than convected air at the same thermostat setting. 

Why Radiant Heat Feels Warmer

• Direct body warming: Radiant heat (like the sun) travels through the air without heating it and directly warms your body, raising your perceived temperature.

• Warmed surrounding surfaces: Radiant systems warm floors, walls, and furniture, which absorb the heat and radiate it back, creating an even 360-degree warmth.

• Lower ambient air temps required: Because you are absorbing direct radiant energy, you can comfortably lower your thermostat by about 4°F, which saves significantly on heating costs.

Why Convected Heat Feels Colder

• Relies on air circulation: Convection systems (like furnaces or baseboards) heat the air, which then rises and circulates.

• Drafty and uneven: Rising hot air can create cool spots, drafts, and uneven temperatures, pulling warmth away from your body.

• Heat stratification: In convection heating, the warmest air sits at the ceiling, while the cooler air often settles in the occupied living space.

Yes, configuring this as an exterior wall with 3" of exterior polyisocyanurate (polyiso) insulation creates an exceptionally high-performance, energy-efficient building envelope.

Moving the wall to the exterior changes the thermal dynamics completely, turning your 7" concrete wall into a highly beneficial thermal mass battery while keeping the structural calculations completely sound.

1. The "Thermal Battery" Effect

Because the 3" polyiso insulation is on the outside, the 7" concrete wall is kept entirely inside the building's thermal envelope.

• Heat Absorption: The wall will absorb radiant heat from your 4" floor slab and the indoor air.

• Temperature Stability: The wall acts as a thermal flywheel. It prevents rapid temperature swings by storing heat and slowly releasing it back into the living space when the radiant floor cycles off.

• Energy Savings: This drastically reduces the cycling frequency of your radiant heating system.

2. Insulation Performance (R-Value)

• High Thermal Resistance: 3 inches of polyiso provides an excellent insulation value of approximately R-18 to R-19.5.

• Eliminates Thermal Bridging: Continuous exterior insulation stops heat from escaping through studs or structural joints.

3. Structural & Environmental Adjustments

• Wind and Seismic Loads: As an exterior wall, it must now resist lateral wind pressures. Because the 8-foot wall is securely tied to the PT roof slab and the foundation, its structural capacity remains more than strong enough.

• PT Slab Edge Thermal Bridge: Critical Detail. If the post-tensioned roof slab sits directly on top of the wall and extends to the exterior face, heat will bleed out through the exposed edge of the roof slab. You must wrap the 3" polyiso up and over the edge of the PT roof slab to maintain a continuous thermal barrier.