Replies

1. 
   DaveRicheson | Dec 09, 2008 10:58pm | #1

   I guess I should add do I need to heat the basement any if at all.

   Is the basement unfinished? Do you plan to finish it?

   Insulating ducts in unconditioned crawl spaces and attics is good. Insulating ducts in conditioned spaces is unnecessary.

   If a space is cold enough to require insulated supply ducts, it is also cold enough to require insulating the returns.

   You can likely insulate the basement walls  and condition the whole basement for just about the same amount of labor as wrapping existing ducts. Material cost may be more, but you are adding more conditioned space to your house.

   More information about the type of basement, use , etc. would be helpfull.

   
   

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   Edited 12/9/2008 3:00 pm ET by DaveRicheson

2. 
   jonblakemore | Dec 10, 2008 12:24am | #2

   On a side note, I would look at duct sealing prior to insulation. You will get a much better ROI.

    

   Jon Blakemore

   RappahannockINC.com Fredericksburg, VA

3. 
   USAnigel | Dec 11, 2008 07:43pm | #3

   Insulate all ductwork, even the stuff inside the house. This cuts the heat/cool loss on the way to the room in need.

1. 
   DaveRicheson | Dec 12, 2008 12:16pm | #4

   Huh?

   Heat loss into a conditioned space is not "lost." It is still inside the conditioned  part of the building envelope. Duct sealing however is another matter, even in a conditioned space. Loss of cfm can be a significant factor in delivering the neccessary btu(s) to any specfic area.

   Duct sealing and insulation are both needed when a duct passes through an unconditioned space.

1. 
   USAnigel | Dec 12, 2008 04:26pm | #5

   I understand the "heat loss" is to the conditioned space but as the "heat" travels to the far end of the house this heat loss can be high.

    I feel it would be a good idea if this heat energy were contained until it reached the room it was intended for. Sealing the duct work is very important too.

   Just like insulating the hot water pipe because you want the heated water to stay hot till it gets to the sink.

4. 
   kurt99 | Dec 12, 2008 06:37pm | #6

   Heat loss is dependent on the temperature difference between the duct and the basement. It is at the very least proportional to the temperature difference (Conduction is proportional to the temperature difference, convective is proportional to the square of the temperature difference and radiation is proportional to the cube of the temperature difference). Assuming that the basement is 50F, the return air 70F and the supply duct air 120F, the payback on insulating the supply ducts is at least three and a half times greater than that of the return ducts (Temp diff of supply 120F-50F=70F, temp diff of returns 70F-50F=20F. 70F/20F=3.5)

   The payback on insulating the supply ducts is probably quite good. The payback on insulating the return ducts will not be as good. There are so many variables that it is impossible to say with the information given whether insulating the return ducts is the best investment in your insulating dollar. Its return is probably the same as insulating under the floor but additional attic insulation, better windows, new weatherstripping around the doors or sealing air leaks around lights, wires, vents, etc. into the attic may have a better payback.

   Don't forget to seal all the possible air leaks in both the supply and return ducts before insulating.

1. 
   DaveRicheson | Dec 12, 2008 08:59pm | #7

   Your 120F-50F makes an assumption that the heat source is natural gas or propane. Use a heat pump, either air to air or ground scource,and the supply  air temp drops to closer to 95F. Still a 45 degree delta T, but nearly as rdical as the 70 degrees of your example.

   The only way to determine what the actual delta T would be is take temp readings of the unconitioned basement and the the supply air. My bet would be that unheated basement will be between 60 and 65 degrees F depending on how much duct leakage there is. Cut in a couple of supply vents in the basement and the space becomes semi-conditioned, the delta T gets smaller and the return on investment for insulating the ducts gets harder to justify.

   For me the material and labor cost would be better spent insulatng and sealing the basement, then making it part of the conditioned space. I have sen very few retro fit duck insulation jobs that actuall achieved any saving on energy cost unless they were in ancold attic or crawl space. Course I'm in a relatively mild climate compared to nortern reachs of the country, so your milege may vary.