Passive Heating and Radiant Floors

The cold weather has arrived in the northern states of America and other regions of the world. Heating is needed around the clock for houses in many of these winter months. This is especially true for single-family homes or stand-alone dwellings. This typology is known as exterior load dominated buildings, or ones that have most of the heat exchange occurring through exterior walls and roofs. Compared to multi-family housing units (interior load dominated buildings), which benefit from a lower exterior wall surface area to interior space volume ratio, single-family houses have a large amount of exterior wall exposure to the outdoor climate. This means there is more surface area for heat exchange to occur – resulting in heat loss during the winter season. Properly insulated exterior walls and roofs can help reduce the heat loss while properly oriented windows can help improve solar gain to the interior spaces.

Emphasizing solar gain opportunities in your house will improve the natural heating for the winter. Having windows oriented facing south to accept the direct sun during the mid-day will benefit the heating addition to your indoors. This is known as a direct gain passive heating strategy in architectural design. Direct gain heating can be combined with thermal mass materials, such as concrete and masonry, to further stabilize the indoor temperature from day to night. As these materials absorb the sun during the day they continue to heat up while holding the heat energy for longer periods of time. This is because certain materials have a high heat capacitance (water and waxes being some of the highest), which allow for heat retention and storage. By the time night rolls around and temperatures are dropping, and the thermal mass is no longer receiving direct sun, these materials will begin to slowly release their stored heat energy to the surrounding environment. The thermal mass with direct solar gain is a great passive design strategy for keeping your home’s spaces warm during the day as well as the night!

Thermal mass can be integrated as the exposed floor material - concrete floors are wonderful for this and can be beautifully finished and decorated with seasonal rugs. Thermal mass can also be integrated as the exposed interior wall material – masonry or concrete walls are common for this and can have an earthy and grounded feeling to them. The thermal mass wall will need to be positioned across from a window so that the sun’s rays can reach the wall directly. When these direct gain with thermal mass strategies are located in smaller perimeter spaces or adjacent rooms to the primary living spaces, they can be used as indirect gain systems. This often occurs with sunrooms, sun-spaces, or fully enclosed and sealed porches. These adjacent spaces can serve to absorb the radiant heat during the day while keeping it building up due to the greenhouse effect. At night, the warm air from the sunroom can be vented into the main parts of the house.

These indirect solar gain systems are sometimes designed within the exterior wall itself, known as a trombe wall system. The trombe wall is a layered wall system, with exterior glazing, a large air-gap (usually 4”-10”) and then a thermal mass wall directly behind the air gap and glass. The challenge with most trombe walls is that your space will not receive any of the natural daylight since the glass is just providing a trap for radiant heat inside the wall system. The trombe wall functions similar to the sun-space in that the wall will have operable louvers or vents that can be opened up at night to allow the heat into the habitable rooms. This passive heating design strategy is more often implements in larger scale buildings as it can be a more costly exterior wall solution for single-family residences. However, if you balance the cost benefit for passive heating over 30-years of living in the house, it will pay-back very well!

Active heating systems can be used in combination with the passive strategies to enhance the amount of heat that might be needed at times and in certain locations. Some active heating systems are more effective than others when it comes to addressing human thermal comfort. The primary goal of heating your home is to keep you and your family members warm and comfortable. As humans, we tend to occupy the floor space of our homes where we walk, sit, and near where we sleep. In some cases, you might have a sleeping loft that is leveled up high above the floor in a room, but otherwise most beds are located relatively close to the floor. The challenge with the heating season for occupied spaces is that heat naturally rises and so most warm air in our homes is continuously moving upwards to the ceiling. So, it can be difficult to keep the occupied zones that you inhabit feeling warm enough.

The most effective active heating strategy for human thermal comfort is a radiant floor system. Radiant floor systems come in a few different forms. In their original form, they are comprised of hydronic pipes that loop underneath a finish flooring layer. They continuously cycle warmed fluid through the pipes, which transfers into the floor by conduction (direct contact) and thus warms the spaces above the floor. Radiant floor heating provides a consistent and stable warmth throughout the space that it covers. It can be put in as a retrofit in selected spaces or included in the entire house with new construction. Because the heat is being moved with liquid and transferred by conduction it is much more efficient than central air systems. Air is the least efficient fluid for transferring heat because it is a gas, and the molecules are far apart. Just like heat pumps, the radiant floor system can be switched over to a cooling fluid in the summer months.

If you don’t have the depth in your floor for the fluid system or are otherwise concerned about potential leaks in the system, there are some electric floor mat options. There are standard electric radiant floor mats as well as carbon-fiber floor mats. Both of these forms remove the fluid in the system and consist of a much thinner cohesive floor underlayment. In comparison to the hydronic loop radiant heating system, the electric mats require a little bit more energy on your electricity bill. The hydronic system can be integrated with a passive solar heating unit (typically located on your roof) to work with very little to no energy from the grid.

No matter which option you consider, radiant floor heating is a great solution if you are already planning to make some floor finish updates or flooring renovations. The active radiant flooring system can be combined with the passive direct gain concrete floor! It is a beautiful combination for the modern eco-friendly home. These heating systems are clean, low energy, low environmental impact, and healthy for effective human comfort.

If you have any questions about the best heating systems for your home, reach out to AIDA, LLC today for a consultation.You can always find more information and healthy home resources at Aletheia Ida Design and Architecture, LLC (AIDA, LLC) at www.aletheiaida.com.