or two to eliminate sagging. Using tie wraps, insure ducting is appropriately fastened to
each supply air grill.
Another important consideration is the physical size of the supply air grills. Four inch
round grills require a 4.5 inch hole and the duct merely slides over the neck of the grill.
A four inch rectangular grill usually measures 4x8 inches for the hole size but also
requires a plenum or transition box behind the grill, also measuring 4x8 inches and
extending approximately four inches behind the wall. These boxes are needed to attach
the air duct to the grill and are required for every size rectangular supply grill.
We suggest that you lay out a simple sketch of your boat on paper and then over lay your
ducting scheme. Take this diagram on board and make measurements to be assured that
the scheme is attainable. Remember once committed, "holes are forever". If you need
help or would just like to discuss your installation with an experienced technician, give
us a call. Mermaid will be happy to aid you in the layout of your duct and venting
scheme.
5. Return Air :
Sufficient cabin "return air" back to the air conditioner is just as important to the cooling
of the boat and the performance of the air system as "supply air" is going into the cabin.
Air conditioning is just that, conditioning of the air in a closed environment by
continually pulling it back into the air conditioning unit, removing heat and moisture and
sending it back into the room or cabin.
It is important that the same volume of air being forced into the cabin is allowed to return
to the air conditioner. As long as the physical opening of the return air grill is at least the
minimum size specified below for your specific air conditioner, the actual shape of the
grill is not important. Where it is not possible to have a single return grill multiple grills
may be used. Make sure that the air conditioner evaporator (the front of the air
conditioner resembling an automotive radiator) is not blocked or restricted from
receiving the cabin return air. It must always be at least 3 or more inches from any bulk
head or structure. Never stow items such as life preservers, bedding or other items of this
nature between the evaporator and the return air grill. To allow better access to the air
conditioner compartment during installation, do not attach the return air grill until the
unit has been completely installed.
RETURN AIR REQUIREMENTS
MODEL BTU SQ. INCHES OF RETURN
M-5 5,200 96
M-6 6,500 96
M-9 9,000 96
M-12 12,000 140
M-16 16,500 140
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