You’re not alone! The ancient Koreans and Romans didn’t not like cold floors either. To keep warm, the Romans channeled hot air under the floors of their villas. The Koreans channeled hot flue gases under their floors before venting them up the chimney.
Fast forward to the modern age. Radiant floors are still keeping toes toasty in modern homes.
The water tubes are typically placed in a concrete slab or in a thin layer of gypsum poured over a wood subfloor. The hot water tubes are sometimes installed the tubing beneath the subfloor between the floor joists. In this case, heat is transferred to the floor by wide aluminum fins.
Advantages of Radiant Floor Systems: The popularity of radiant floor systems is based on their many advantages. Rooms with radiant floors feel warmer than those with unheated floors at the same air room temperature. Cool floors absorb many more heat waves from your body than they give back. In this uneven exchange you feel a coolness. The surface temperature of a radiant floor may be 10oF to 200F warmer than a conventional floor.
Radiant floors provide more even heat, especially those imbedded in concrete or gypsum which have significant thermal mass. They are quieter than forced air systems which have fan noise. Radiant floor heating also eliminates the leaky ducts, draft and dust problems associated with forced-air heating systems.
Radiant floors use lower water temperatures than hydronic baseboards heater which requires 160° F to 200° F water. The water temperature needed to heat tile radiant floors is typically 120oF, but can be as low as 90°F to 105° F for floors with less thermal mass. This makes radiant floors a good match with a low-temperature heat source like an air- or ground-source heat pump, or even an active solar system. Also, producing lower temperature water puts less heat stress on your boiler, helping it to last longer.
Some Cons: When turning on the heat, it will take some time for the radiant floors to get warm. When heating a concrete slab-on-grade, which is not insulated, there will be heat loss into the ground. By simply insulating a slab-on-grade from below and on the sides, it will become much more comfortable in cool weather, even without radiant heating.
Radiant floors are expensive to install and to repair. Also, in super-insulated green homes, does it really make sense to install an expensive system which only supplies a little amount of heat? Radiant floors cannot be used for cooling and dehumidification, as can forced air ducts. Also, they do not have the capacity to filter the air as does a forced air system.
Conclusion: An widely quoted article in Environmental Building News, 2002 by Alex Wilson summarizes the utility of radiant floors as follows:
“In homes with conventional levels of insulation and typical glazings, radiant-floor heating is an extremely comfortable heat-distribution option. It does not contribute to IAQ (Indoor Air Quality) problems, and it might well even save a little energy if homeowners can be convinced to turn down their thermostats to a level that will provide the same level of comfort as a house without radiant heat. But in an extremely well-insulated, green home, radiant-floor heating usually is not the best option. If you’ve gone to all the effort and spent all the money to achieve a truly stand-out energy-conserving envelope with passive solar gain, why not offset that cost by dramatically reducing the cost of the heating system?”
In a cold climate, an insulated foundation keeps your home’s bottom warm and dry. And it can save on your heating bills and improve your quality of life.
The greatest need for foundation insulation is in cold climates where the average winter soil temperature is 500F or less. In these situations the house can lose lots of heat to the soil.
A home’s foundation is hard at work doing all sorts of stuff: It supports the house and connects it to the ground. It protects the interior from soil moisture, humidity, and insects. It also helps in maintaining a moderate interior temperature. When adding insulation the above factors need to be kept in mind.
In areas with hot humid summers, cool basement walls condense moisture out of the air. This creates excellent conditions for mold and mildew. Insulating basement walls keeps them warmer and less likely to form condensation.
A homes foundation comes in different configurations such as slab on grade, crawlspace with low foundation wall, and basement and high foundation walls. Each foundation type poses different problems and opportunities.
Got Waterlogged Soil? Help your foundation to fulfill its duty of keeping you dry! Before installing any insulation, make sure that your foundation’s surrounding soil or backfill does not become waterlogged. Check that the drainage grade around your home slopes at least 10% downward. Install or repair gutters and dispose of roof drainage at least 10 feet away from your home’s walls. Move any irrigation systems away from the home’s perimeter. If you have a perimeter drain, check that it is in operating order. If you have poor drainage, consider installing a perimeter drain.
Let’s face it. It’s not practical to insulate under a slab in an existing home. However, there is good news. The slab’s sides can be exposed and insulated. And more good news: heat loss through a slab occurs mostly at the edges. This means that insulating the edges of a slab has a good return on investment.
The U.S. Department of Energy estimates that, in most parts of the United States, just insulating the exterior edge of the slab can reduce heating bills by 10%–20%! Waterproof closed cell foam is most often used as the insulation material.
Most crawlspaces are not insulated, but vented to the exterior by crawlspace vents. However, exterior crawlspace ventilation may not work so well in climates with humid summers. In these situations, the vents can bring in more humidity than they take out. When warm, humid outside air flows across a cool wood or masonry crawlspace surface, condensation may result. And in freezing climates, it may be hard to keep ventilated crawlspaces warm enough to prevent water pipes from freezing. Finally, a cold crawlspace causes losses of heat from the heated rooms above.
For these reasons, there is a trend towards non-vented insulated crawlspaces for new buildings or retrofits. Non-vented crawlspaces are only feasible if effective moisture controls, air sealing, and insulation are in place. Without outside venting, the crawlspace becomes part of the home’s conditioned space. This enables effective control of crawl space summer humidity and winter chill.
The U.S. Department of Energy estimates that basement insulation can reduce natural gas heating bills of $250 to $450. This approximates 10% to 20% of the heating bill. Basement insulation is also essential for a comfortable finished basement.
Basement walls are buried deep in the soil, exposed to surface water drainage, ground water, and humidity. No basement waterproofing system is perfect. Inevitably some liquid water and water vapor penetrates through the basement wall. In addition, cool basement walls condense moisture from the outside humid air which leaks into the basement. Due to failure to address these multiple sources of moisture, many basement insulation retrofits have resulted in moldy walls with horrible smells. This discussion owes much to an in-depth technical guide to basement wall insulation, by Lstiburek and Yost
Most basement insulation in older homes is installed on the interior surface of the basement wall. Unfortunately, the insulation is often not installed correctly.
According Lstiburek and Yost, any interior basement insulating wall system must have the following properties:
• It must be able to dry to the interior should it become wet since the below grade portion of the wall will not be able to dry to the exterior during any time of the year. This precludes an interior polyethylene vapor barrier or any impermeable interior wall finishes such as vinyl wall coverings or oil/alkyd/epoxy paint systems.
• The wall assembly must prevent any significant volume of interior air from reaching the cool foundation wall. Thus it must have an effective interior air barrier or a method of elevating the temperature of potential condensing surfaces (such as rigid insulation installed directly on the interior of concrete or masonry surfaces).
• Materials in contact with the foundation wall and the concrete slab must be moisture tolerant; that is the materials should not support mold growth or deteriorate if they become wet. However, moisture tolerant materials are not necessarily capillary resistant. That is, some materials may tolerate being wet without blocking the passage of liquid water through the materials. A capillary break must be placed between these materials and moisture sensitive materials.
Figure 1 shows a typical interior insulation retrofit of a basement wall. The foam insulating board will not deteriorate or support mold when wet. It is carefully installed so that it blocks interior basement air from reaching the interior surface of the concrete wall. This prevents wall condensation when humid air is present. The concrete wall dries to the interior: water vapor passes through the foam board and wall board which are permeable to water vapor. If necessary, a dehumidifier can be used to dispose of excess wall moisture.
(Important Cautionary Note!: A very common mistake, in installing insulation on interior basement walls, is to place a polyethylene sheet, or other vapor barrier, over the insulation. This prevents the wall from drying to the interior. The result: wet insulation, mold, odors, and wood rot.)
Exterior basement wall construction is best applied when the building is constructed. A convenient retrofit opportunity for exterior insulation occurs if the wall exterior is excavated for the installation or repair of a perimeter drain. Due to the expense and technical difficulties of excavation, cost effective insulation retrofits may only expose and insulate a half of the wall. Heat loss savings, from installing a double-thick layer insulation on half a wall, are comparable to the savings from insulating the whole wall with single thickness.
Figure 2 shows a typical exterior insulation retrofit of a basement wall. Moisture resistant foam board is installed on the exterior surface of the concrete wall, which has been sealed with rubberized asphalt. A dual-purpose drainage mat is installed on top of the foam. The mat protects the foam and directs soil drainage downward. A perimeter drain, if present, disposes of the downward drainage.
The damp concrete wall dries to the interior: water vapor passes through the foam board and wall board which are permeable to water vapor. If necessary, a dehumidifier can be used to dispose of excess wall moisture.
The exterior form insulation keeps the concrete wall warm, and enables it to act as a thermal mass to reduce temperature swings. The warmth of interior concrete surface keeps the wall dry by preventing condensation caused by humid interior air.
Foundation insulation is essential for an energy efficient, comfortable home in cold climates. It is also cost effective, savings hundreds of dollars in heating bills annually. Before retrofitting, take any measures needed to prevent waterlogging of the soil or backfill surrounding the insulation.
For basement walls, a retrofit which places insulation on the wall exterior is the technically best option. It keeps the basement walls warm which prevents condensation and add to comfort. Nevertheless, most retrofits place insulation on the interior of basement walls. This avoids the expense and pitfalls of excavating the wall.
Heed Lstiburek and Yost’s advice! For both exterior and interior retrofits, it is essential that the damp concrete basement wall be allowed to dry to the interior. This prevents moisture from becoming trapped in the wall, and avoids the risk of bad odors, mold and woodrot.
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