Radiant floor systems are relatively easy to install in buildings with unfinished
basements offering easy access to the underside of the main-level floor.
Aluminum heat-emission plates, like the homemade plates shown above, are
sized to fit between floor joists. One or two grooves bent into the flat plate
accommodate pex tubing.
of heat. Modern radiant floor heating systems
can operate at much lower temperatures than
traditional hydronic heating systems — typically
around 100°F ( 38°C) — because the radiators
are very large, in this case the whole floor of the
building. This is the critical point when relating
to solar heating because solar heating systems
typically operate at relatively low temperatures.
It is common to see solar storage tanks operate
within the 100°F to 150°F range ( 38°C to 66°C),
while traditional baseboard heating systems typically operate at 180°F (82°C).
When it comes to finding the radiant heating system you’d like to install, it soon becomes
obvious that radiant floor-heating systems are
the most common type in the United States.
Radiant floor heating has been refined in Europe
for 50 years, but it’s only caught on here in the
last 15 years. I have mentioned radiant wall-and radiant ceiling-heating systems as viable
When it comes to finding
the radiant heating system
you’d like to install, it soon
becomes obvious that
radiant floor-heating systems
are the most common type
in the United States.
options, and while these types of systems have
been the norm in Europe for at least 25 years,
they remain rare here in the States. The radiant options we have to choose from are radiant
floors, walls and ceilings.
mula that has been used very successfully; access
it at solartoday.org/ramlow. You can also find
several sizing methods in my book, Solar Water
Heating, A Comprehensive Guide to Solar Water
& Space Heating Systems.
Storing Heat for later Use
This article focuses on solar heating systems
with heat storage, whereby solar heat collected
during sunny hours is stored for use later. The
two popular options for heat-storage media
used in solar space-heating systems are water
(or a water/antifreeze solution) and some type
of solid, like sand. Note that whether you use a
water tank or sand bed for storage, backup heating is required in virtually all climates.
Space heating in cold climates requires a
substantial number of solar collectors, and finding enough room for them may be difficult. For
most existing buildings, the final size of the collector array will be limited to available space for
them. Next, if you’ll use water for heat storage,
you will need to identify a place for the water-storage tank. Lastly you will need to identify the
radiant heat-delivery system that will work best
for your building.
Since the beginning of the modern solar era
in the mid-1970s, the most common type of
heat storage has been water. My article, “Warm,
Radiant Comfort in the Sand” (SOLAR TODA Y,
November/December 2007), compares water
and sand for heat storage. Water storage offers
precise temperature control and high efficiency,
but it is limited to one or two days of heat storage. Sand-bed storage offers long-term storage
capacity for installations where winters are long
designing Heat delivery for retrofit
Two popular retrofit systems are the least
invasive to install: radiant floor or radiant wall
panels, with water for heat storage.
For situations where you want to install a
solar heating system into an existing building, the
best choice is a water storage system with radiant
heat delivery. For new construction, you have the
water and high-mass sand-bed storage options.
The first step when considering your storage options is to size the solar energy system to
meet your heating needs. Sizing space-heating
systems can be a challenge, but two resources
can walk you through it. My SOLAR TODAY
article mentioned previously details a simple for-
Radiant floor systems are relatively easy to
install in buildings with unfinished basements
offering easy access to the underside of the main-level floor. If you are lucky enough to have this
situation in your building, your installation can
be fairly easy. Aluminum heat-emission plates,
usually about 2 feet ( 60 cm) long, are sized to fit
between floor joists. One or two grooves bent
into the flat plate accommodate pex tubing. You
run the pex tubing between the floor joists, snap
the pex into the plate and staple the plate to the
underside of the floor. Insulation is then installed
under the plates to ensure all the heat dissipated
by the plates radiates up.
Another radiant floor system uses what I call
a track plate — a flat aluminum plate fastened
to strips of plywood. These track plates come
in different sizes, but imagine a 12- by 24-inch