08/30/2007 4
EI203
5.
OTHER PLENUM EQUIPMENT - Auxiliary equipment such as humidifiers, zone plenum dampers, etc.,
located within the plenum which may cause a non-uniform airflow will have to be removed. Zone dampers
within the trunk line at least 12" from the HeatChoice typically are no problem. When horizontal zone
dampers are involved, perform all check-out functions with smallest zone open first.
Comment – zone dampers cause back pressure on the blower and overall reduced airflow. The
HeatChoice elements should be staged according to the heating load required by the various zone
combinations. The Electro Industries’ WarmFlo series plenum heater is designed for zone systems and
should be investigated for forced air zone applications.
6.
AIR CONDITIONING “W” OR “M” COILS - These new coils represent a double “A” or an “A” with a
third slanted side. The net result is the top point no longer lines up with the center deflector of the
HeatChoice frame. The only known solution is adequate space between the coil top and the HeatChoice
unit itself. Also we have no direct experience to know how much space is required, we are suggesting a
requirement of at least 12” between the top points of these new coils and the bottom of the HeatChoice
frame itself.
7.
INSUFFICIENT COLD AIR RETURN CAPACITY - Installation experience indicates this is a major
concern. In fact, it could represent a problem in as many as 6Ø% of the installations, especially if there is a
requirement to increase airflow with the existing blower and the existing cold air return capacity is already
undersized or restricted. Check the static pressure within the return cabinet or the suction at the filter
cabinet door. Do not assume because there is a register on the wall, the hole behind the register or the
passageways are equal to this register. Sharp offsets and transitions in the cold air return system often cause
severe restrictions. Expect to add additional registers or a relief register in the main cold air return duct.
8.
BLOWER CFM CAPACITY - The furnace forced air system must have an airflow capacity larger than the
minimum requirement on an HeatChoice specification sheet (see "SPECIFICATIONS - TABLE 1") or the
HeatChoice nameplate. It is near impossible to correctly measure CFM airflow in an existing residential
installation. Experience and rule of thumb indicators will have to be followed to determine the existing
furnace CFM capacity. The following may be helpful:
a.
Existing furnace nameplate - Typically represents a high or optimistic rating and is a function of
the systems static pressure. What changes have been made to the heating system since
installation?
b.
Blower motor size - Used only as a minimal guide.
10 kW unit - 1/4 HP or larger
15 kW unit - 1/3 HP or larger
20 kW unit - 1/2 HP or larger
25 kW unit - 3/4 HP or larger
c.
Observe/examine airflow ducting system and design - Use duct sizing table (ECØØ1), or
industry equivalent duct capacity airflow charts and determine if the system is capable of
delivering the CFM required on the nameplate. Especially check the number of registers and
the number of “6 inch rounds”. The same would apply to cold air return duct capacity.
d.
Calculated CFM - By measuring the temperature rise across the existing furnace (or this electric
unit), the CFM can be approximated. The accuracy of this formula will depend upon the
estimated or determined Btu output (actual heat energy across the furnace).
CFM = Btuh (output)
Temp. Rise x 1.08
