Insulate Basement Ductwork

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Insulate Basement Ductwork Podcast:

Tim Carter received the following email from Mike not too long ago:

"Tim - I have an unheated basement. The ducts for heating/AC run through the basement. Do you suggest insulating the ducts in the basement to conserve more of the heat before it moves to the rest of the house?"

This is a very common question.

The answer to insulate the ductwork is not straightforward.

Look at this photo:


insulate basement ductwork

This ductwork is insulated. But there's a far greater issue with it! The idiot installers didn't reduce the size of the trunk duct as they took off runs to the rooms. The static pressure at the end of the trunk will be pitiful.

When you insulate basement ductwork, the Btus created by the furnace are still inside the home. You'll not conserve any energy.

The air coming out of the ducts may be a little warmer, but the temperature in the rooms of the house will still be at whatever you have the thermostat set to.

It's simple high school physics. See, the teacher was right! She told you that you'd use the knowledge one day!

CLICK or TAP HERE to get FREE BIDS from local HVAC people who can insulate the ducts in your home should you think I'm wrong.

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5 Responses to Insulate Basement Ductwork

  1. Thanks for the answers. I do have some comments to add some context. I have a raised ranch with single zone heat where the ductwork for the bedrooms is exposed in the garage and family room. In the summer when we bought the house, I found it would "rain" in the garage when the AC was running. The humid air in the garage would cause the ducts to sweat profusely and drip. Since I did not care about heating or cooling the garage, I put insulation around those ducts which stopped the rain and, in my opinion, allowed more of those BTUs to service the actual living space. This, in my opinion, is because the garage is extremely leaky, so any heat applied there is wasted. The ducts in my family room are not insulated, so they do as you have said which is to shed some heat into the lower level of the home. So, my conclusion would be that to insulate ducts may or may not be useful, depending on where they are exposed. You mentioned an attic (yes needs insulation), but I would add a leaky garage to that list.

  2. Don't the ducts help heat the basement? It can be the coldest area of the house unless there is some way of circulating the furnace heat.

  3. If you don't insulate your ducts, it will cost you more because you're losing energy to somewhere you don't want to heat. However, hot air rises. That will rise up against your floor, and warm it. So, that's good. If you need some heat in the basement anyhow, you might as well warm your upstairs floor along with it.

    If you have an open crawl space, garage, or basement where you never go, then insulate your ducts. Otherwise, you're heating the outdoors.

  4. Hi Tim,
    I really like your reasoning on this subject, and agree wholeheartedly. Since my home workshop is in my basement, and there are not any heat sources there, the sole heat comes from the hot air ductwork when the furnace is on. Interesting note.... the colder it is outside, the more the furnace is on, and the warmer my shop stays! I do sometimes have to use a small ceramic heater to supplement the ductwork-supplied heat when temps are 'medium' and the furnace doesn't run very often, but this is just fine by me. I stay comfy as you say by 'layering up' my clothing to stay warmer.

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