of the most useful design features of Runtal is the ability to
curve the radiators to match the curved walls of today’s
modern building designs. Runtal radiators can be field-curved,
or factory-curved, depending on the model chosen and the
Field curving is
the preferred option, since it is the least expensive, and the
most flexible choice. Model types “R” and “RF” in lengths over
15’-0” can be field-curved, as long as the curving radius is
over 15’-0” as well.
The longer the radiator, and the larger the curving radius,
the easier it is to field-curve.
Long sweeping expanses of glass walls can be effectively and
economically heated with field-curved R or RF radiators,
creating a custom look heating design at a price only slightly
higher than straight wall design.
curving is the option of choice if the radiator, or the
radius, are either less than 15’-0”; or Runtal models R2F or
RS2 are required. Factory curving is a more expensive and more
inflexible option, with the radiators being hand-built to a
and curving radius limitations apply, so consultation with a
Runtal Representative is highly recommended prior to
specifying factory-curved radiators.
The design water temperature drop through traditional hydronic
heating equipment is typically figured at a 20°F drop (20°F
DT). This is because traditional heating equipment utilizes
round water tubes in its design. At water temperature drops
greater than 20°F
DT, the water flow rate is so low that it
produces laminar flow through the round tube. With laminar
flow, there is little or no heat transfer between the water
and the round tube, and the heating equipment does not produce heat.
Runtal, on the other hand, utilizes flattened water tubes for
our designs. The water flow through flattened water tubes is
turbulent, even at extremely low flow rates; assuring
excellent heat transfer between the water and the flattened
tubes. Water temperature drops of 40°F DT, or even 60°F
are possible with Runtal.
Designing with larger design water temperature drops can lead
to great savings in the overall cost of a heating system. For
example, designing with a 40°F DT in lieu of a 20°F DT means
that the required flow rate is cut in half, to provide the
same heat output:
Flow Rate = (Heating Capacity) DT (DT X 500)
Half the flow rate means smaller piping, less insulation,
smaller pumps, smaller expansion tanks, etc – all leading to a
lower cost for the heating system.
In Europe (where energy costs are much higher) almost all
hydronic heating systems are designed around water temperature
drops of 40°F
DT or more to save pumping energy costs.
with Runtal, there are two main layout options em ployed:
perimeter style or wall panel style.
long lengths of Runtal radiation wall-to-wall or
column-to-column is the most popular layout option for
commercial and institutional applications. Since the entire
length of a Runtal panel is the active heating element,
perimeter style Runtal spreads the heat out along the entire
perimeter, giving wall-to-wall comfort. Runtal builds
radiators in even 2” increments up to 29’-6” in length, so
most applications can be served by a custom-sized single long
panel, tailored to fit the perimeter space. Typically a pipe
trim is provided on each end to hide the connecting piping and
individual wall panels in a room, usually centered under
windows, is a more “Euro-style”look for utilizing Runtal. This
style is most popular in renovations of old buildings, where
individual windows are placed at intervals along the exterior
walls, or where niches were originally provided for old cast
iron radiators. For the wall panel style radiator, the piping
connections to the radiator are typically done with decorative
shut-off valves, and no pipe trim covers are used. Depending
on the Runtal model chosen, the radiators can either help to
modernize the look of the room, or compliment the original
classic style of the space.
end piping, where the supply and return heating water piping
are both at one end of the radiator, can lead to tremendous
savings in on-site piping and cost. Single radiators, or a
series of up to three radiators may be piped in a same end
An example of this
savings potential would be a situation where it would be
difficult (or impossible) to get a water return pipe to the
far end of the radiator (or series of radiators). Same end
piping allows both the supply and return water piping to be at
the accessible end of the radiator.
Same end piping
also evens out the heat output along the entire length of the
radiator series. This is because the warmest supply water on
the piped end is coupled with the coolest return water; while
at the non-piped end, the coolest supply water is coupled with
the warmest return water.
important application of same end piping is in multi-story
buildings with vertical stacked risers and open perimeter
bays. With a single set of centrally located vertical supply
and return piping risers, it is possible to run Runtal
same-end series radiators up to three bays (at 30’-0” maximum
per bay) in each direction from the central riser set. Up to
180’-0” of perimeter could be handled with just one set of
risers, with no additional return piping required.
Additionally, the heat output is relatively constant along the
entire series, assuring a comfortable environment for the
It is important to
note that due to the baffling method used to separate the
water flows in same end series radiators, only three radiators
(regardless of the radiator’s length) should be piped in