Table of Contents
What is the maximum length for a flexible air duct?
1 Length Limitation. Factory-made flexible air ducts and connectors shall be not more than 5 feet (1524 mm) in length and shall not be used in lieu of rigid elbows or fittings. That’s a pretty strong limitation.
Does Flex duct reduce airflow?
Friction is the enemy of airflow. Unlike rigid ducts, which are cut to length within a tolerance of 1 inch or less, it’s easy to cut a length of flexible duct that’s several feet longer than is needed to get from point A to point B [2A]. That creates slack in the duct, which reduces airflow for two reasons.
Should I replace metal duct with flexible?
Flex ducts are better for existing trunk-and-branch heating and cooling systems. Metal ducts are more rigid due to the nature of steel, making them ideal to build an entire HVAC system. Installation. In comparison to metal duct, flex duct is easier and faster to install.
How do you split a flex duct?
Now, let’s get to the steps of splitting your flex duct. Step 1: Primary Calculations. At the very first, you need to perform a manual J load calculation. Step 2: Identifying The Point Of Splitting. Step 3: Cutting The Duct. Step 4: Joining The Ducts. Step 5: Use Straight Runs. Step 6: Pulling It Tight. Step 7: Test & Balance.
How often should flex duct be supported?
Supports should be installed at least every once 4 feet. The maximum allowable sag in flexible duct is one-half inch per foot.
Why is there a shortage of flex duct?
1.) The flex duct commonly used in Southern California relies on a heavy-duty stainless steel spring for its core. Stainless steel, it turns out, is one of many simple commodities that regularly runs out this year. If duct manufacturers can’t get ahold of stainless steel, they can’t make flex duct.
How long does insulated flex duct last?
What is the functional lifespan of a flexible duct system? A search of industry articles, blogs, and chat rooms indicates it lasts from 10 to 25 years. Most flexible duct manufacturers warranty their products for about 10 years.
When hanging flexible duct the hanging material should be at least?
When hanging flexible duct, the hanging material should be at least: 2 inches wide and spaced no further than every 5 feet.
Can you insulate flex duct?
Install flex duct that is pre-insulated with a layer of fiberglass blanket insulation covered with a foil or plastic vapor barrier. Use insulated duct for all supply and return ducts located in unconditioned space.
Why must flexible duct be stretched slightly for straight runs?
to prevent system noise and vibrations from transmitting through the duct system. Why must flexible duct be stretched slightly for straight runs ? To reduce friction and reduce the chance of the duct collasping inside.
What is the disadvantage of flex duct?
The downside of flex ducting is that it is considered temporary with an acknowledged lifespan of only about 15 years. Another major disadvantage is that they are a little too flexible, so they are often incorrectly installed. And with greater friction than metal ducts, proper sizing is critical.
Should flexible ducting be pulled tight?
Flex duct should pulled tight to reduce inner air resistance. It should be supported with straps that are a minimum 1.5″ wide. The straps need to be spaced no further than 5 feet apart, but closer is better.
Are flexible ducts good?
Pros of Flexbile Ductwork Flexible ducts are cheaper than metal ones. This can save you money on installation and upkeep. That means they can be installed in tight spaces where traditional metal ducts wouldn’t fit. If you’ve got sharp corners and lots of angles, flexible ductwork is a good option.
What is the most commonly used ductwork in an HVAC residential system?
Made of galvanized steel or aluminum, rigid sheet metal is the most common type of ductwork. The thick, solid wall makes the duct very durable.
Can you use flex duct in crawlspace?
Flex duct is commonly used in crawl spaces. That said it is vulnerable to punctures, animals and other hazards. Animals have no particular reason the chew the ducts, but sometimes they will anyway. Flex duct is cheaper to install than hard duct, and (at least initially) it is easier to make it not leak.
How do I know what size flex duct I need?
Measure the length and width of the room where the flex duct will be supplying the air. Multiply the length and width together to get the square footage of the room. For example, a 10-by-10 room will be 100 square feet.
What size return duct do I need for a 3 ton?
Electric heat pumps shall be tested in accordance with UL 559 or UL 1995. Example: 3.5 ton heat pump. The duct for this system must be sized by using 6 square inches of clear duct area for each 1000 BTU of cooling. Each ton of cooling contains 12,000 BTU.
What size duct do I need for a 12×12 room?
A 12×12 foot room will need a 4×8 inch supply duct to get an adequate CFM rate, which is about 144 CFM.
