Ducting and its thermal resistivity


Flexible duct is what we use to transport all that heated/cooled air from your air-conditioning unit to your house. When looking at getting a system installed, or upgrading an older system, many people tend to overlook the importance of this essential component. We believe it’s generally due to 3 reasons;

  1. The client is uneducated in the importance of the duct work
  2. The installer fails to mention it’s importance. This may be in a hope that they will be able to install a cheaper (and less thermally resistant) duct in order to reduce their installation cost, thus winning the competitive bid for the works
  3. It’s a good way for the builder to reduce in their costs and the client is none the wiser

So in this brief post I’ll try and explain the ins and outs of duct, so you can be well equipped when it comes time to making the big decisions in regards to your HVAC installation.

Flexible duct has come a long way, and amidst the hype that says flexible duct should NOT be used as a main air transfer system, we believe it has a place in our residential installation IF it is installed correctly.

Generally there is only one main factor that you have to take into consideration, and that is the ‘R’ Value. The ‘R’ value denotes the ducts thermal conductivity, or its resistance to heat flow through the ducts thickness. The reliability of the words printed on the side of the duct can be misguiding, and it has a lot to do with how the insulation rating is tested. Generally, the insulation is tested ex-manufacture, meaning the rating of the insulation has been determined before it has been manufactured. Degradation of the insulation occurs when the duct is squashed into bags (when being transported). Some degradation can occur during installation; for example if the duct is squashed between building structures etc., or if the duct suffers from prolonged stretching or compression!

Increasing your ducts ‘R’ rating has several benefits with only one downside – increased initial investment cost. At CMS we recommend the highest rated duct you can afford. It will pay dividends in the future.

Below are a few of the benefits to upping your ‘R’ rating.

  1. Reduced running cost
  2. Better temperature transfer to outlets in your house
  3. Reduced temperature loss into your roof or subfloor
  4. Less run time on your machine

The standard duct that will be installed in your installation will be ‘R1′ but we have the option to increase to ‘R1.5′, ‘R2′ and ‘R2.4’.

Ask us today about installing better insulated duct for your new or existing system!

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