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 |
5,200 | 96 | |
6,500 | 96 | |
9,000 | 96 | |
12,000 | 140 | |
16,500 | 140 | |