Insulation to Duct - Heating Only

[iken]

Just a quick question.

Is it necessary to insulate duct, that is supplying warm air only (no cooling) to an open area. The entire duct run is exposed in the area which it is serving.

I feel this would be extra dollar value, that will not add any real benefit. As I understand it, condensation will occur on cooler surfaces in respect to the surrounding area. This will never be the case, as the unit will be heating only (or at worst delivery fresh air from outdoors with no treatment).

Any other opinion would be greatly appreciated.

Thanks

 

[GMcD]

It depends on what the supply air temperature is in the duct versus the ambient air temperature where the duct is, and whether that will affect the final discharge air temperature at the air outlets/terminals. Normally, if the supply air temperature is less than 20F (12C) different than the ambient air, insulation is not needed. But, if the SAT is more than 25F (14C)higher than ambient, and you want to make sure that the air temperature being delivered at the air terminal is within a few degrees of what's needed for design, then yes, insulate the duct.

 

[MintJulep]

iken,

Your undestanding is not quite correct.

Condensation will occur if the outside surface temperature of the duct is lower than the dewpoint of the air in the space around the duct.

Depending upon where this equipment is located, it is possible for this to occur if you have cold outside air in the duct and relatively warm, moist air in the space.

 

[iken]

Thanks for the reply.

GMcD - The duct is located in the same area as the air is being discharged to, so I do not see any temperature loss through the duct being an issue. My main concern was for condensation.

MintJulep - This was my belief also, although not stated. However the air being delivered will always be warmer or at the same temperature as the surrounding area being served, so I guess my asuumption of no insulation was correct.

Thanks again

 

[LIKALA7]

Iken, in a heating scenario the risk of condensation occurring is on the inside of the duct. Since the air in the duct moves with a velocity and it is not likely to drop below it's dewpoint there is no need to insulate the duct.

The same can't be said for the cooling mode because the risk in this case is of condensation occurring on the outside of the duct and because there may be pockets of air around the duct that are stagnant, condensation could occur. It is therfore advisable to ensure that return air flows over the supply air duct in the cooling scenario thereby preventing it's cooling below it's dewpoint and thus avoiding condensation.