Use metal flex or fiber board ducts that are insulated to code.
Ac ducts in attic.
In more cases than not a 3 ton ac with the ducts in the attic has a ton or so of load that s just from the location of the ducts in the attic and the associated duct gains leakage etc.
The doe s building america program recommends beds buried encapsulated ducts.
An attic can get up to about 130 f in the summer and the conditioned air entering the ducts is about 55 f or so.
So if the thermostat is sitting at 74 degrees the air being pushed into the duct system is going to be right around 54 degrees.
The duct insulation should include a vapor barrier cover.
If you ve studied heat transfer at all you may recall that the rate at which heat moves from a warmer to a cooler body depends on the temperature difference which we abbreviate as δt.
So water is condensing on your ac ducts.
Since burying ducts is simply one of several ways to address the energy waste associated with the decision to locate ducts in a vented unconditioned attic it s worth taking a fresh look at all of the possible solutions to the attic duct problem.
In last week s blog i discussed the practice of burying attic ducts in deep insulation.
If you have central heating and or air conditioning in your home the warm or cool air is delivered to each room through a system of connected ducts and vents.
When hvac ducts are installed in a vented attic in a dry climate bury the ducts in attic insulation to protect them from temperature extremes in the unconditioned attic space.
Why is this a problem.
The remaining 2 tons of capacity is at least 1 5x oversized for the actual 1 load.
If they are located in your attic be sure the area is properly insulated and any cracks or holes are sealed.
First water dripping off of your ducts and onto your insulation can cause the insulation to compress which decreases it s r value or ability to insulate.
Install ductwork so that it is in direct contact with i e laying on the ceiling and or truss lower cords.
Heaping insulation over the ducts is fine in dry climates but can cause condensation on the duct insulation jacket in humid climates.
If we take into consideration that on a hot summer day the attic where your ducts live can be as warm as 150 degrees that 90 100 difference in the temperature is what can cause the condensation to begin.
Keep ducts spaced apart so air can flow between them.
Put it in an attic full of blown insulation.
Reduce the humidity level around your air ducts.
If ducts are located in a crawlspace underneath your house cover the soil to reduce moisture.
When water condenses and drips into your attic or home it can cause a some serious secondary problems.
