HVAC Ductwork in Basement, Insulation?

[Fortress67]

I have a forced hot air hvac system. The round metal ducts in the basement are run in open Joists. During COVID I had time and I wrapped each duct with the cheap plastic bubble insulation.

Now the question: IF you could get cheap or free fiberglass batt insulation would you go thru the trouble of cutting it up and packing it in around the ductwork? Then maybe adding something like they use for the return ducts (basically cardboard with an aluminum coating) to cover it up and sealed off? Yes, I will need an access point for the dampers.

But would the result be worth the time?

 

[WillyBoy]

OK, you add to the efficiency of the heat supply for upstairs. This makes the basement colder. This increases the delta T across the floor into the basement. How much heat loss is there from the basement to the outside?
I've chosen not to insulate the basement ductwork because that's where I spend a lot of time in the winter, working on projects. I think the net heat loss for the entire building wouldn't be significantly different either way.
Of course this assumes the the rim joist is reasonably well insulated all the way around the structure and the interior of the basement walls are insulated to below the frost line outside.

Any HVAC engineers willing to throw in? I suspect the calculations would depend on a lot more than the factors that have been discussed.

 

[NUTTSGT]

Like @WillyBoy mentioned, it will make the basement colder, however, it should make the upstairs warmer due to less heat loss as the air is moving through the duct work.

Do you use the basement to the point of needing the extra heat down there ?

If you need the extra heat, you could add a duct register in the plenum, one that can open/close.

 

[duneslider]

What is your basement like? If you never plan to finish the basement then insulate the ducts and the whole floor/ceiling, and you should be good. My basement stays a fairly consistent temp year round and I don't really think it affects the temp in the ducts that much. Insulating my basement ceiling didn't seem to make any difference in the temp downstairs, or the air in the ducts. My basement pretty much stays 65-68 year round.

 

[Superbowl]

Like others have said, the heat loss from the ducts will warm the basement which can be a plus if you use it.

No insulation at all on a duct can be a problem in summer because if there is humidity down their water can condense on the ducts and drip into places where mold can grow.

 

[minke]

I don't think the upper house will get warmer. I presume that the thermostat is up there.

 

[larry4406]

None of our new home construction has insulated ductwork internal to the thermal envelope. This includes unfinished basements. Our equipment is located in the basement. Zone 1 serves the basemen and first floor, while Zone 2 serves the second floor. Zone 1 stat is located on first floor while Zone 2 stat is located in the master on the 2nd floor.

Our equipment is sized and installed for the entire envelope, whether the basement is finished or not. We also include registers in the unfinished basement and a cold air return. This tempers the basement and keeps it from smelling funky.

Only ductwork inside the thermal envelope that is insulated is makeup air and fresh air lines which are pulling in outside air. These can sweat in the summer.

I would not waste my time or $$$.

 

[fitter30]

Heat rises. The loss from the water heater and duct still go into house. I'd would be more concerned about air leaks at joints especially rectangular duct mainly at the corners were two pieces come together. Duct sealer works good.

 

[mm08822]

Only ductwork inside the thermal envelope that is insulated is makeup air and fresh air lines which are pulling in outside air.

Makeup and fresh air lines are one in the same and just 2 sets of controls for different purposes?? Or are they truely 2 different mechanical systems?

 

[NUTTSGT]

I don't think the upper house will get warmer. I presume that the thermostat is up there.

Correct, technically not warmer but it should get up to the t-stat set temp faster.

 

[Superbowl]

Makeup and fresh air lines are one in the same and just 2 sets of controls for different purposes?? Or are they truely 2 different mechanical systems?

Make up air goes to a gas/oil furnace or other things that draw air and vent to the outside. Fresh air makes up for the carbon dioxide you breath out.

 

[larry4406]

Makeup and fresh air lines are one in the same and just 2 sets of controls for different purposes?? Or are they truely 2 different mechanical systems?

Makeup air is used by the range hood when the hood is over 399 cfm. Makeup air is admitted when the hood runs.

Fresh air is new air introduced to maintain proper air quality within the home. Our houses, these systems run 10-15 minutes every hour pulling in outside air.

Broan used to make a system that did both. So, a single inlet duct, landing of wiring from both controls, and the one device did both functions.

That Broan device had a recall, discontinued, etc.

Since then, we have two separate ducts, one for each function.

Our gas combustion devices are sealed combustion and use outside piped air for combustion and do not pull from the space

 

[larry4406]

Make up air goes to a gas/oil furnace or other things that draw air and vent to the outside. Fresh air makes up for the carbon dioxide you breath out.

Close

Makeup air is for the range hood.

Fresh air is for air quality.

Combustion air is for fuel burning appliances. New homes this is negated as they are sealed combustion devices pulling direct from the outside. Old homes, yes need a source of combustion air usually provided by a drafty house.

 

[mm08822]

Close

Makeup air is for the range hood.

Fresh air is for air quality.

Combustion air is for fuel burning appliances. New homes this is negated as they are sealed combustion devices pulling direct from the outside. Old homes, yes need a source of combustion air usually provided by a drafty house.

So a makeup air system contains one inlet only and a fresh air system includes an inlet and outlet for exchanging equal volumes of air?

 

[larry4406]

So a makeup air system contains one inlet only and a fresh air system includes an inlet and outlet for exchanging equal volumes of air?

Makeup air is dumped into the house somewhere whenever the range hood runs. Otherwise nothing. Inlet duct and range hood duct working somewhat in tandem.

The fresh air system we have dumps the outside air into the return plenum and creates a fan demand on the air handler to circulate air. There is not an outlet duct for this. I don't know the CFM's involved but its not huge based on feel; something akin to a powerful fart fan bringing in outside air is my guess. I guess in a perfect world, it is pressurizing the house to some extent but practically, I think its within accepted normal leakage of the envelope. I am sure there are some systems that use ERV's for this (ducted in/out) but we don't have these and I am not sure when those systems come into play.

 

[mm08822]

Makeup air is dumped into the house somewhere whenever the range hood runs. Otherwise nothing. Inlet duct and range hood duct working somewhat in tandem.

The fresh air system we have dumps the outside air into the return plenum and creates a fan demand on the air handler to circulate air. There is not an outlet duct for this. I don't know the CFM's involved but its not huge based on feel; something akin to a powerful fart fan bringing in outside air is my guess. I guess in a perfect world, it is pressurizing the house to some extent but practically, I think its within accepted normal leakage of the envelope. I am sure there are some systems that use ERV's for this (ducted in/out) but we don't have these and I am not sure when those systems come into play.

Ok, I had the ERV in mind.

 

[Crazyjake8493]

I wouldn't waste my time or energy with it. You'll heat the upper floor(s) faster at expense of a colder basement.

The time and energy would be better spent air sealing and insulating your rim joists and sealing up any basement windows.

 

[ripperd]

For the heating season I don't think it makes a big difference. Heat rises, the heat generally will make it to the first floor.

If you have central AC going through the same ducts though that changes things a little. Basements below grade generally stay pretty cool all on their own. The extra cooling provided by the ducts is unneeded and wasteful since it detracts from the amount of cooling to the upper levels. And the cold won't really migrate upward like the heat does in the winter.

 

[Fortress67]

Thanks for your input.

Other things people asked or i thought of:
Basement unfinished and will stay that way forever. I am down there alot but i can put a coat on if needed.
Rim joist is Insulated with 2x required by code. (again got it free)
Yes ducts used for AC.
About 40% of the Basement is above grade.
No Insulation on basement walls, Just the CMU and Drylock.
Only one small window and one insluated man door that leads to the Garage
I did seal all the basement supply ducts joints with aluminum duct tape before I wrapped them.
As for the return ducts, I also cleaned the inside and sealed with caulk and or tape as needed. I also did this during the shutdown so I had all the time in the world.

But the feeling i get is like everything else on the internet. Some say do it and some say don't.

 

[PoorUB]

If it is heated, conditioned space thier is no need to insulate the duct. If it is attic space that sees whatever temperature the outdoor temps are then it needs to be insulated. This sounds like an older home with an uninhabitable basement. Just used for storage, water heater and furnace. If the temperature in the basement doesn't mater. Then sure, insulate. Also, the basement is considered conditioned space as you prefer to keep it at a reasonable temperature, not freezing ar extremely warm.
Insulating the ducts will do no harm, but might be a waste of time and not improve your heat or AC. More important is to use duct seal and seal all the connections.

 

[duneslider]

If you aren't insulating the ceiling or the walls in the basement you are just likely to make the basement feel cooler which will make the floor of the house cooler. Not sure that will help you in the long run. The basement is considered a conditioned space since it is connected to the floor above and not sealed off. At the end of the day, I just don't see it doing anything. It would be better time spent to insulate the basement walls.