Insulate Old Ductwork vs Replace It With New Insulated Duct?

Insulating old ductwork is a cost-effective way to improve your HVAC system’s efficiency. But it only works if the ducts are in good condition. Otherwise, ductwork replacement with insulated ducts might be your only option.

In this Pick HVAC Ductwork Insulation Guide, we cover pros and cons of both options plus information about cost.

Read This First: If you’re considering new HVAC equipment, don’t replace the ducts until a pro does a load test to determine what size system is right for your home. Why? Because a lot of HVAC systems are too big, and as a result are less efficient than they should be and don’t create the indoor comfort you want. If a technician decides you need a smaller system (or larger, in rare cases), the size of the ductwork might need to change.

On the other hand, if the ductwork is the right size for your new system, and it is in good condition, insulating old ducts will save you money over replacing it with new ductwork. Plus, it might be possible to get a higher R-value, or better insulation value, than replacing it with insulated ductwork.

Overview – Ductwork Replacement vs Insulating Pros and Cons

We dig deeper into these below, but here is a quick glance at the advantages of both approaches.

Insulating Old Ductwork

Pros:

  • Reduces Air Loss
  • Cheaper than replacement
  • DIY is Possible
  • Makes ducts quieter

Cons:

  • Makes for ugly ducts
  • Might not be as energy efficient
  • Can be a messy DIY project

Replacement with Insulated Ductwork

Pros:

  • Good efficiency
  • More options
  • New ducts will last longer

Cons:

  • More expensive
  • Potential airflow issues with insulated flexible ductwork
  • Must be properly sized for your HVAC equipment

The Choice

Old ducts can waste energy and make your home less comfortable than you’d like. What’s the answer – repair of old ductwork or replacement?

Ducts in bad condition leak air, and the Department of Energy suggests leaky ducts waste 20% to 30% of the energy used to heat and cool the air.

Insulate those ducts, and a $100 gas bill for heating can be cut to $70 or $80. Similar savings can be realized in warm climates that require a lot of AC use.

Spend $300 to insulate existing ducts, and your cost will be paid back in 2-4 years tops.

On the other hand, replacement with insulated ducts might save you another 20% in energy efficiency on top of the 20%-30% you save from eliminating leaks. The payback period might be a little longer, since replacement costs more than insulating the ductwork, but your HVAC system will be more ecofriendly through an overall reduction in energy use.

As seen in the tables above, both insulating and replacing ductwork has a number of advantages and disadvantages.

Let’s look at both options in detail.

Insulating Existing Ductwork Overview

You have several options for insulating existing heating and AC ducts. You can wrap in fiberglass batts or rolls and taped. Rigid foam board can be glued to it. Or it can be covered in spray foam insulation ($$-$$$).

Each insulation type comes in a number of different R-factors. The higher the R-factor, the more resistant to heat flow the insulation will be. Your cost for insulating existing ductwork will depend on the R-factor of insulation you choose and how much ductwork you will need to make your HVAC system more efficient. The better insulation provided by the material, the more it will cost – but the more you’ll reduce your energy costs too.

Insulated vs Uninsulated Ductwork

Why not just leave your ductwork as is - uninsulated? There are four reasons why insulated ductwork is better than uninsulated ductwork:

  • It is in unheated space, such as a garage or in a basement with no heating ducts
  • It is in hot space, like an attic
  • It is in a humid place like the basement, and when the AC is running and cool air is flowing through it, moisture condenses on the ductwork and drips onto the floor, drop ceiling or whatever gets in its way
  • You want to reduce energy use and monthly utility bills!!!

Replacing Existing Ductwork with Insulated Ductwork Overview

Replacing your existing ductwork with new ductwork that is insulated is a labor-intensive project that might be best left to a professional HVAC contractor. There are many options available when it comes to insulated ductwork. Your choices are fiberglass insulated flexible ducts, sheet metal ducts lined with fiberglass insulation, and a fiberglass duct system. Of the three choices, the flexible ductwork is the cheapest and can be used in very tight areas and around obstacles. It bends easily and is easy to work with.

Fiberglass duct systems are very strong and do an excellent job of not allowing heat or cool air to leak out of the duct work. This type of system seems to last longer than the flexible ductwork. Fiberglass ductwork is also very easy to clean when compared to other types of ductwork.

Finally, sheet metal ducts lined with fiberglass insulation are a strong sheet metal with insulation on the inside of the ducts. This type of system does a great job of reducing heat loss and also prevents the build-up of condensation or moisture on both the inside and the outside of the ductwork system.

Fibrous glass vs fiberglass: Owens Corning and a few other manufacturers refer to some types of fiberglass insulation as “fibrous glass.” As you can see from the name, they are synonymous. We mention this for clarification – when you see “fibrous glass,” understand that the ductwork is made with fiberglass.

Cost

The cost to insulate the heating and AC ducts in your home with fiberglass insulation is between $1.00 to $2.00 per square foot when installed by a pro. You can save roughly 50% of the cost by DIY. Adding rigid fiberglass or foam to ducts costs $2.00 - $4.00 per square foot, and the cost of spray insulation averages about $5.00 per square foot.

The cost to replace your existing ductwork with insulated new ductwork is higher than simply insulating your ductwork. Including material, removal of existing ductwork, and installation of insulated ductwork, you can expect to pay between $10-$20 per linear foot. The price varies depending on what type of insulated ductwork you choose to install with your heating and cooling unit.

Get more details in the Pick HVAC Ductwork Price Guide – the most comprehensive ductwork buying guide and information source on the web!

Conclusion

Have your utility bills gone up without the cost of energy rising or without using your HVAC system more? Check your ductwork before you call an HVAC technician. An inspection of the exposed ducts might turn up gaps where heated and cooled air is escaping, not doing its job, and driving up utility costs.

If checking the ducts isn’t something you want to do, call an HVAC technician. Explain that your HVAC efficiency seems to be reduced and you suspect it might be the ducts. Start there. If it turns out to be ductwork issues, then:

Ductwork repair vs replacement is your choice – insulating what you have or replacing it with insulated ductwork.

Here are four scenarios to help you decide which is the better option:

1. Your ductwork is less than 20 years old/is in good condition: Insulated ducts that are performing as they should. Don’t replace what isn’t broken. Improve its energy efficiency by adding insulation.

2. Your ductwork is less than 20 years old but needs repair: Fix it and insulate it. Make sure all joints are secure and taped, and then insulate all exposed surfaces. You’ll save up to $14 per square foot by repairing and insulating ductwork vs replacing ductwork with insulated ducts.

3. Your ductwork is old and needs repair: Get quotes for replacement and for repairing and insulating them. Consider the costs. Consider how long you plan to live in the home. Will you get your money back from the higher cost of replacement? Or is repairing and insulating the ducts a more cost-effective short-term fix because you’ll be selling in a few years?

4. Your HVAC system is nearing replacement age: Don’t do anything before you get estimates on a new system and have a load test (Manual J and/or others) to determine system size and whether your current ducts are the right size and type. The last thing you want to do is spend money on your ductwork now only to have to replace it in a few years when you replace your HVAC system.

What if it isn’t the ductwork?

Other common causes of lower efficiency in an HVAC system are dirty air filters, dirty coils in the air handler and condensing unit and low refrigerant due to a leak.

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