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Radiant Solar Heating

Radiant heating relies on infrared energy to transfer heat directly to people and objects in a room. This is very different from heating the air, which is how liquid (baseboard) and forced-air systems work. Radiant heating has a number of advantages. First, it is more efficient that baseboard heating because it does not require the high temperatures that baseboard heating does and is almost always more efficient than forced-air heating because there is not heat lost in ducts.

Radiant heating is also beneficial for those with allergies because there is not air movement in this system. No air movement means dust and other allergens are not stirred up and blown through the air. Also, there is no air intake on these systems, so outdoor air and all of its allergens are not brought into a living space.

When it comes to installing radiant heat, there are two different mechanisms that can be used and three places that panels can be installed. Wall and ceiling panels are similar and will be treated together. Floor heating is a bit different and is treated in its own section.

Radiant Floor Heating

The concept of radiation floor heating, regardless of energy source used, is that warming the floor will keep the rest of the house warm as the hot air rises. It is important to note that these systems perform best when a large thermal mass is located in the floor, such as a concrete slab, and when the flooring is hardwood, tile, or linoleum. Carpeting tends to insulate the floor and prevent the transfer of heat into the room.

Though air is used to heat flooring in some applications, it is generally a poor choice and will not be discussed in depth. It is the least efficient and most difficult to construct system, thus it is seldom used and not recommended as a radiant heating mechanism.

Electric Resistance

This is, by far, the most common type of radiant heating used in floors. It consists of cables built into the floor or electric mats that are laid underneath the flooring. These systems generally use a thermal mass concept to keep costs down as electric heating can be quite expensive.

In most cases, a concrete floor or slab will underlie the hardwood, tile, or linoleum in a home. At night, when electrical costs are low, the concrete will be “charged” or heated up. It can then store enough energy to keep the home at a comfortable ambient temperature for up to 10 hours. When combined with appropriate passive solar warming, this system can work quite well.

The drawback to such a system, as might be imagined, is the fact that it heats the home at night. This means it cannot utilize solar energy. If PV systems are used, then electric radiant heat can be 100% solar and only rely on grid energy as a backup. Overall, electric radiant heating is not the best system in terms of cost or energy efficiency for people looking to use solar.

Hydronic (Liquid systems)

Hydronic systems are the most popular and the most cost effective systems. In these systems, water or an antifreeze solution can be heated using passive solar collectors. The liquid is then circulated through pipes in the flooring rather than being stored in a tank as in standard solar hot water systems. These systems are usually closed, direct-loops and if distilled water is used they are very low maintenance.

The drawbacks to hydronic systems are the high initial upfront costs, difficulties if maintenance must be performed, and possibility that they cannot provide all of the heat a home may need. Many of these systems are tied into backup systems that burn traditional fuels.

Ceiling and Wall Panels

These systems usually rely on either electricity or hot water to heat a metallic panel mounted to the ceiling or wall. These systems are generally used for supplementing radiant floor heating and are seldom used on their own. The reasons for such usage patterns are as follows.

First, because the panels are substantially smaller than the floor space in the room, they usually are not effective in creating extensive heat. They can heat a small area of a room, but often not the entire space. Most panels have a low “heat capacity,” which means that they are very quick to warm up, but also very quick to cool down. This feature makes them useful for rooms that are used less often used because, while they cannot provide substantial heat, they can provide it quickly. If electricity is used, these panels are not the best options to be matched with solar.

The second reason these panels are generally poor at space heating is their location. Rather than being on the floor and providing the full potential for heat rise and warmth, they are located at greater height. This means that the heat they give off is limited to line-of-sight and that they rest is lost to the ceiling, a place where humans spend little time! The best heat from these systems is achieved when directly in front of them, which presents the problem that they often heat a person’s head more so than a person’s feet. Most people find this uncomfortable.
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