Radiantly Heated Floors

Floors can be heated by electrical resistance wires, warm air circulating through multiple ducts, and warm water circulating through coils of pipe to warm the surfaces of concrete or plaster. Heated floors warm feet by conduction, and set up convective currents to heat the room air evenly. Tables and chairs can block IR waves coming up from a floor, thereby blocking heat to the upper body.

Without good insulation, heated floors can't pro- X vide all the heat needed in a cold climate unless the floor is brought up to a temperature too hot for feet. Rugs and carpets reduce the efficiency of heated floors. Heated floors can't react quickly to small or sudden changes in demand, due to the high thermal mass of concrete floors. Repairs are messy and expensive.

Hydronic radiant panels are better used in floors than ceilings. Hydronic radiant heating systems circulate warm water through metal or plastic pipes, either encased in a concrete slab or secured under the subfloor with conductive heat plates. They are directly embedded in concrete cast-in-place floors. Radiant coils under wood floors are quite popular. A rug or carpet over the floor will interfere with the exchange of heat. Special under-carpet pads can help with heat transfer, or higher water temperatures can be used.

The water supplied for radiant heating may be heated in a boiler, heat pump, solar collector, or geo-thermal system. In response to a thermostat setting, a control valve in each coil adjusts the supply water temperature by mixing it with cooler water that has been circulated already. Adjacent spaces must be insulated, as radiant panels generate very high temperatures, and there is the strong potential for great heat loss. With higher insulation, smaller panels can be used. They are usually located near exterior walls, but this may not be the case in solar-heated buildings, where they can supplement areas that aren't heated well by the sun. Copper was formerly used for the piping, but connections could fail, so synthetic one-piece systems are now used.

Electric radiant floors aren't appropriate for every home because of the cost of electricity, but they can be an excellent solution to certain design problems. Choosing the right system means knowing what you want it to do, and looking past manufacturers' claims to the system's real costs and benefits. Electric systems are easier and less expensive to install than their hydronic counterparts. They're also less expensive to design for different zones. They can be used to heat a whole house or to provide spot comfort in kitchens and baths.

Electric radiant floor elements can consist of cables coated with electrical insulation (Fig. 24-7), or of fabric mats with the cables woven into them, which are more expensive. Like hydronic tubes, electric elements are embedded in the floor system. Cables are usually embedded in a 38-mm (1.5-in.) thick slab of gypsum underlayment or lightweight concrete. As with hydronic tubing, you need to consider the ability of the framing to support the slab's weight and make adjustments to window and door heights for the slab's extra thickness.

Mats generally require less floor thickness than cables, and can often be placed in a mortar bed beneath floor tiles. This adds as little as 3 mm ({in.) to the floor height. Some mats can be rolled out on the subfloor beneath a carpet and pad. Mats are available in a range of

Electric cables will be covered with thin slab of concrete or gypsum.

Figure 24-7 Electric radiant floor:

Electric cables will be covered with thin slab of concrete or gypsum.

Figure 24-7 Electric radiant floor:

standard and custom sizes and shapes. Mats heat up a tile floor faster than buried cables, but the thermal mass of the cable system will keep the floor warm for a longer period of time.

Hydronic radiant heating systems can use gas, oil, electricity, or even solar energy as their energy source. On the other hand, electric cables don't require a boiler, and may be more cost-effective for small floors. An electric system for a small bathroom could cost $300 to $400, compared to $4000 to $5000 for a hydronic system, not including fuel costs, which are generally higher for electric systems. Electric floors are often used to supplement heating systems in homes with forced-air systems. Highly efficient homes with thick insulation, airtight construction, and passive solar features may also be appropriate sites for electric floors.

Getting Started With Solar

Getting Started With Solar

Do we really want the one thing that gives us its resources unconditionally to suffer even more than it is suffering now? Nature, is a part of our being from the earliest human days. We respect Nature and it gives us its bounty, but in the recent past greedy money hungry corporations have made us all so destructive, so wasteful.

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