How to Insulate Sheet Metal AC Ducts

How one can Enhance Furnace and AC Effectivity

Many individuals spend quite a lot of cash shopping for new furnaces and air conditioners which have 98% effectivity rankings. That’s nice! I’m a giant advocate for vitality effectivity. Nevertheless, how environment friendly is a furnace or central air unit if the ductwork is filled with leaks?

Seal Your Ducts!

Metallic is just not simple to work with. It might probably solely be bent in sure methods and items of metallic are put collectively to type a chunk of ductwork. The ductwork normally doesn’t match completely collectively and thus there are leaks. These leaks are accountable for about 20% of the lack of effectivity of a heating or cooling system.

So how do you repair it? Easy. Seal the ductwork.

Ductwork insulated and air sealing with closed cell polyurethane spray foam insulation



Insulating your ducts

Including insulation to your ducts is not so simple as getting some duct wrap and taping it collectively. Okay, some folks and contractors do insulate their ducts this fashion. And technically, the ducts are insulated afterward.

However should you go this route, you are forgetting one thing tremendous essential: duct leaks.

Duct leaks are the scourge of vitality effectivity and indoor air high quality. Gaps, cracks, holes, rusted out corners… When air leaks by your ducts, it brings contaminants into your indoor air and reduces the effectivity of your HVAC system. By not addressing duct leaks, you are actually polluting your clear, filtered, conditioned air with soiled, unfiltered, unconditioned air!

Bear in mind, a variety of your ductwork is both in your crawlspace or your attic. Do you actually need to be respiration the air from these areas 24/7?

Anyway, the purpose of all that is to focus on the truth that you have to seal the leaks earlier than you insulate the ducts.

Insulation blocks the motion of warmth, however it might probably’t stop air leaks. Soiled air will nonetheless enter your ductwork by the leaks, even after you add insulation. Should you determine to insulate your previous ducts, simply be sure to or your contractor follows this order of operations:

  1. Seal the leaks with mastic or mastic tape (we comply with a extremely exact “seal and take a look at” protocol that identifies all leaky areas and leads to 4% duct leakage or less).
  2. Wrap fiberglass duct insulation across the ducts and tape the seams collectively.

In fact, you may also contemplate…

Ductwork Insulation in Totally different Places

How one can Insulate Ductwork in Attic

To be fully sincere, you need to attempt to keep away from putting in ducts in a vented unconditioned attic. In case ‘the injury had already been executed’, transfer the ducts inside your own home’s thermal envelope.

Your private home has ducts within the attic if there are vents in your ceiling. And in case you’re planning on leaving the ductwork there, then you definately would undoubtedly must insulate the system.

Putting in insulation in unconditioned areas is perhaps a bit tough as it’s good to keep away from ‘sweating’. Because of the drastic temperature modifications, condensation may seem on the ductwork and that’s one thing that have to be averted in any respect prices.

The very first thing that you need to do is locate and restore any leaks. After that, you possibly can start insulating utilizing one of many strategies that we’ve got already talked about above or you possibly can strive going for blown-in cellulose insulation: 

  • Be certain that the ducts are situated on prime of the rafters.
  • Use a high quality hose and blowing machine.
  • Attempt to absolutely cowl the ducts with cellulose.
  • If there are any uncovered areas left, you should use insulating blanket materials.

Insulation Round Ductwork in Ceiling

There are fairly just a few disadvantages to having ducts within the ceiling. Warmth rises and if it begins within the ceiling, it doesn’t actually have anyplace to go. In consequence, you’re utilizing your furnace inefficiently. 

Nevertheless, you probably have ducts within the ceiling and that the area is well-insulated, there is perhaps no want in insulating the precise ductwork

Ought to I Insulate Ductwork in Basement?

The primary factor that you need to keep in mind is that insulating the ductwork within the basement will make the area a lot colder. When you’ve got loads of drains and water pipes operating by the basement and you reside in an space with tremendous chilly winters, then the pipes may freeze and burst within the winter.

To keep away from that, you should use an electrical heating tape wrap and apply it to the pipes. Or you possibly can contemplate insulating each the basement partitions and the ducts.

Insulating Ductwork in Crawl Area

Similar to your attic, the crawl area is an unconditioned space with nice temperature fluctuations. You must undoubtedly set up furnace ductwork insulation as it will make it easier to save vitality and cash (together with money saved on furnace upkeep and restore). Insulation, if put in correctly, additionally does an important job at stopping condensation.

You may need to contemplate hiring an expert to insulate your crawl area as it’s difficult to work in such a decent area. 

The most typical kind of insulation used for the crawl area contains foil-faced blanket and spray foam insulation.

So, which is it? Insulate or change?

It is as much as you, but it surely’s usually more economical to replace the ducts. By the point you pay for supplies and labor for sealing and insulating present ducts, it’ll normally shake out to a value that is near what it prices to get new ones.

In case your contractor does issues the best way we do, substitute additionally leads to a greater duct system that retains you extra snug and maximizes effectivity.

With us, you get a model new duct design that’s precisely sized on your residence and your HVAC system. Treasured few HVAC contractors will do that. Most are “field swappers” who simply change what you have got with the identical precise factor. In different phrases, the system will nonetheless underperform – even after the ducts are insulated!

Within the occasion you are already replacing your HVAC system, that is a good time to additionally change your previous ducts. The brand new duct system will decrease vitality loss and, assuming it is put in by a educated firm, will supply higher high quality and luxury in comparison with no matter you’ve got bought now. It is going to additionally pair properly along with your new HVAC gear. Your present ducts, alternatively, may not.

The Selection

Old ducts can waste energy and make your home less

Outdated ducts can waste vitality and make your own home much less snug than you’d like. What’s the reply – restore of previous ductwork or substitute?

Ducts in unhealthy situation leak air, and the Division of Power suggests leaky ducts waste 20% to 30% of the vitality used to warmth and funky the air.

Insulate these ducts, and a $100 gasoline invoice for heating may be minimize to $70 or $80. Related financial savings may be realized in heat climates that require a variety of AC use.

Spend $300 to insulate present ducts, and your price shall be paid again in 2-4 years tops.

However, substitute with insulated ducts may prevent one other 20% in vitality effectivity on prime of the 20%-30% you save from eliminating leaks. The payback interval is perhaps somewhat longer, since substitute prices greater than insulating the ductwork, however your HVAC system shall be extra ecofriendly by an total discount in vitality use.

As seen within the tables above, each insulating and changing ductwork has an a variety of benefits and downsides.

Let’s take a look at each choices intimately.


The price to insulate the heating and AC ducts in your house with fiberglass insulation is between $1.00 to $2.00 per sq. foot when put in by a professional. It can save you roughly 50% of the price by DIY. Including inflexible fiberglass or foam to ducts prices $2.00 – $4.00 per sq. foot, and the price of spray insulation averages about $5.00 per sq. foot.

The price to interchange your present ductwork with insulated new ductwork is greater than merely insulating your ductwork. Together with materials, removing of present ductwork, and set up of insulated ductwork, you possibly can anticipate to pay between $10-$20 per linear foot. The worth varies relying on what kind of insulated ductwork you select to put in along with your heating and cooling unit.

Get extra particulars within the Pick HVAC Ductwork Price Guide – essentially the most complete ductwork shopping for information and knowledge supply on the internet!

Steps for Insulating HVAC Ductwork

  1. Verify the pace of the blower motor on the furnace. If needed, change the wires to cut back the blower to its lowest pace.
  2. Press a steady strip of foil tape to all longitudinal seams alongside straight runs of duct.
  3. Use a paintbrush to use duct mastic to the joints the place an elbow connects to a duct.
  4. Use a utility knife to chop foil-faced fiberglass insulation to the right dimension.
  5. Wrap the insulation across the duct, after which pinch the seam closed. Safe the insulation with brief strips of foil tape.
  6. Apply a protracted strip of foil tape alongside the seam within the insulation. Repeat to insulate the remaining ducts.
  7. To put in preformed duct insulation, begin by disconnecting an elbow to reveal the tip of the duct.
  8. Snap a plastic cap onto the duct finish, then slip the preformed insulation over the duct.
  9. Gently pull the insulation over all the size of duct.

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