SailNet Community - Reply to Topic
Thread: AC and Heat Duct Work? Reply to Thread
Send Trackbacks to (Separate multiple URLs with spaces) :
Post Icons
You may choose an icon for your message from the following list:

Register Now

In order to be able to post messages on the SailNet Community forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
Please note: After entering 3 characters a list of Usernames already in use will appear and the list will disappear once a valid Username is entered.

User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.


Confirm Password:
Email Address
Please enter a valid email address for yourself.

Email Address:


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

  Additional Options
Miscellaneous Options

Click here to view the posting rules you are bound to when clicking the
'Submit Reply' button below

  Topic Review (Newest First)
01-28-2007 12:20 AM
Wayne25 I called the 10" x 4" a diffuser. It is actually a register.
01-28-2007 12:10 AM
Wayne25 1970 Columbia34
You can purchase sleeve insulation made to slide over different diameter round ducts. The sleeve has fiberglass insulation on the inside and a vapor barrier made from vinyl or aluminum foil on the outside and is easy to install. The advantage is they have no lengthwise seams that could void your vapor barrier. They come in 5' lenghts and you tape the joints with foil tape, NOT DUCT TAPE. Duct tape is good on everything but ducts. It is available at any HVAC supply house. United Refrigeration has stores all over the country and world. Make sure the insulation doesn't get wet. If it does, it a perfect place to grow mold. DWG PVC is a good applicationas mentioned earlier, as is electrical PVC conduit. You can buy havy cast aluminum "blast/slide gates" to use as dampers if you can get access to them. Place them at the takeoff of your main duct for less noise at the outlet.
I'm comcerned about the 4" size of your ducts. Look at your specs for the evap fan. If the ESP (external static pressure) capability of the fan is .5" water column then your 4" ducts are probably too small and you will not get your rated cfm for the unit and it will freeze up. If you have a high pressure evap fan that can produce 2" ESP, then you probably have a chance.
There is a product call felxible duct that may be recommended to you. Its easy to install and can snake anywhere and comes already insulated with a vapor barrier. Problem is, it has a very high static pressure loss which reduces airflow and it looks like you already have small ducts. It is used in the HVAC industry to connect ceiling diffusers to the round branch ducts. Good design doesn't allow more than a few feet of it. Cheap designs and installation that use a lot of it usually have airflow problems due to high static pressure losses from the flex.
If you can fit a 10" wide x 4" high register for example, in your design, you can purchase it made from aluminum so it doesn't rust and specify the hoizontal blades to be in the rear of the diffuser. If your mounting high, turn the diffuser so the blades can point down to push heat to the floor. Reverse the blade angle for summer.

01-27-2007 11:33 PM
j34035 In reference to PVC, check with your local plumbing supply for sewer and drain pipe. This is a much lighter pipe than the regular plumbing PVC, and the cross section can be flexed to fit in spaces other pipes cannot. I have used this stuff in the past for ductwork, and it works very well. Also, I second the need to insulate, or you will make a water still on the outside of your duct.
01-26-2007 11:29 PM
RickBowman 1970Columbia34
What type of heating unit are you installing and what are it's ratings? I am currently installing a heated water furnace rated at 40,000 btu with a 3 speed fan blower. 5 seperate euro vents with 2 vents sharing the same 3" duct as this was the only possible way to get a duct in the head and at the inside helm windshield. I have cut 12 holes either 3" or 3.5" through grp depending on whether it was a euro vent or the actual hose that needed to go through it. I am using 3 way ball valves to route heated engine water from the already installed 5/8 inch hose that is connected to the heat exchanger on the heated fresh water supply. I like your diagrams and it appears as though you have some serious challenges with your plan. Knowing what the weather is currently like in Bay City, the air temperature isn't helping much either. Sure hope that you have heated storage, or maybe this is a spring project?


Thanks for the post. I appreciated your reply.

01-24-2007 11:41 AM
1970Columbia34 good idea with the pvc pipe, I am not sure how I could put a control valve in other then on the grate its self. I could make my stacks that come up out of wood and hook pvc pipe into those. its not easy trying to add this to a 1970 sailboat. I plan to run 3 discharges of the 4" to the rear and run one 4" into the v-berth.
01-24-2007 10:11 AM
sailingdog I don't see why you couldn't use PVC pipe, rather than sheet metal, for the duct work... It really depends on how hot the air gets from the heating side of the unit... I am guessing that you're using a heat pump/AC heating unit rather than diesel or propane forced hot air, so it probably wouldn't get hot enough to be a problem. PVC pipe acts as a insulator to some degree, so the heat loss/gain would be minimized, and it is less maintenance than sheet metal, which will rust out...

Even if you use sheet metal for the ductwork, the vent openings could be made from PVC pipe relatively easily, and allow you to open and close the vents as needed.

One issue I see with having the vents directly beneath the ports is if the ports leak, it might cause some problems..
01-24-2007 09:56 AM
1970Columbia34 The problem is running duct runs on the floor is not possible, there is all kinds of things in the way like the water tank sit right next to the only locker the unit will really even fit in. are you saying use pvc pipe for my duct run vs, sheet metal?

01-24-2007 09:51 AM
sailingdog The air return won't really help pull the heat down... heat rises. There should be some sort of insulation you can get for the ductwork, even if it is just a heat-reflective mylar barrier.

What you might want to do is have the ability to open vents at either the top or bottom, and then depending on whether you're heating or cooling, you can open the appropriate vent. It wouldn't be that hard to make a sliding collar type door for PVC pipe.
01-24-2007 09:17 AM
1970Columbia34 Thanks for the responses, ok I have come up with a new idea here i would build 2 of these that would fit in my windown slots and connect the with 4" pipe.

you mention insulating, are the products out there for insulating 4" pipe some sort of sleeve the pipe can slide into? or can i glue some sort of thin insulation to the pipe? what do you guys think of this idea. I know what your saying about the vents being high up but, the unit has a 10x14 return grill right at the floor which i hope helps pull the heat down.

01-23-2007 11:47 PM
sailingdog Aside from Wayne's and Faster's concerns, it would seem to me that the heating/cooling of the boat would be adversely affected by doing it this way. The space between the hull and hull liner is likely to be hot in the summer and cold in the winter, and if you're not using a duct, much of your cooling/heating capacity will go towards cooling or warming the hull and space between the hull and hull-liner. Even an uninsulated duct will tend to help keep the cooling/heating air flow directed towards where it will do the most good.
This thread has more than 10 replies. Click here to review the whole thread.

Posting Rules  
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is On

For the best viewing experience please update your browser to Google Chrome