Radiant Floors

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Talking to builders and going to home shows, radiant heating systems are all the rage.  Unlike forced air systems from a furnace, radiant does not move air and thus is less drafty.  The theory is that because air is not being blown around, there is less loss through windows.  Also, because there are no drafts, people are more comfortable at lower thermostat settings.  Some believe that the added comfort at lower temperatures is why radiant systems can save energy.  My view is that this is a bit counter intuitive since heat is heat.

Radiant heat has been around for years in the form of radiators.  If you have ever lived in a home with radiators, you know that they are always in front of a window to help circulate air by using the convection of cool windows and hot radiators.

Radiant systems generally require either electric coils or hot water to circulate through a mass, in our case a concrete mass in the floor slab.  It can also be mass in the ceiling, but reports from people with such systems are that this is a less satisfying.

One disadvantage of radiant heating systems is that the house remains at a constant temperature throughout the day.  If you like to sleep in a cool room, you will need to open windows or keep bedrooms colder during the day to achieve a superior sleeping environment.  We like to sleep cool, and thus, we will need to balance the system to accommodate our style of living.

Radiant floors also have several additional advantages.  First, the concrete mass can be a great way to collect heat from passive solar design.  Second, the mass can absorb heat during the summer to keep the home cooler.  This will be  a major benefit to us because we have opted to not install an air conditioning unit ... opening windows at night during the summer to cool our floor slab and closing windows during the day to keep room temperature cool.  We live in the Pacific Northwest and this seems to work well in our climate.

Radiant systems are ideal for a heat pump heat source.  Heat pumps are often referred to as a soft heat.  In other words, the air or fluid is heated to a lower temperature than with a combustion flame.  Thus, pumping of the fluid is steady over a longer period than the frequent cycling on and off of a furnace fan. 

Our ground sourced heat pump and ventillation contractor Wayne Medrud, Smart Energy Systems of Yelm, WA, did the radiant layout ... using a nonPVC, Pex tubing system.  We have six zones within the house to allow different levels of warmth to be maintained.  Warm bathrooms, cooler bedrooms, minimalist tubing in the greenhouse so our vegetables don't freeze, etc... Each zone can be regulated to achieve a desired comfort level.

A quick note on the question of radiant barriers.  These are barriers which reflect radiant energy back into a room or away from a roof, generally through the use of an aluminum foil.  We only used window shades in the bedrooms and these contain an aluminum foil that may act as a radiant barrier, but to a minimal degree.

Because of the mild temperatures in the Pacific Northwest, we felt the cost to put a radiant barrier in the walls was over kill and probably not cost effective. There is some research on radiant paints that also can reflect radiant heat back into a room.  Our research was that there were significantly more expensive and contributed at most only a 2% savings.

Final thought ... it is critical to have a competent plumber at this stage.  The water pipes and sewer lines will be fixed in place once the concrete is laid, and thus, the location of the rooms and walls cannot be moved if there is plumbing in them.  We checked, and Brad Thorkildsen, Shamania Plumbing, hit the design walls right on the money.

Passive Solar Heating

In most areas of the US passive solar can be a major contributor to home heating.  Passive solar allows the low in the sky winter sun into the house to heat a storage mass, such as a concrete radiant floor.  Generally, windows are sited due south with reduced windows on the east, west, and north sides to prevent summer heating and heat loss.  As you can see from the photo, sun in January enters the house, As the sun gets higher in the sky as summer approaches, the windows will be shaded by the roof overhang.

Our view of Mount Rainier is to the East and there is another large house to the south of us.  We opted to take the view and forgo passive solar as a primary heating source.  However, the greenhouse is designed to dump heat into the house during that rare sunny winter day. (See the discussion on our greenhouse.)

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Sunday December 17, 2006 05:34 PM -0800

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