Going to insulate my ducts

Feb 4, 2009
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pictures below

I have a new furnace and I’m adding a heat pump, ducts are from 1960 and not sealed. I figure now it the time to do this.
I’m assuming the higher the R value the better (within reason), I’ll need insulation that is thinner because taking the ducts down to wrap will be problematic.
I get the tape and mastic idea so we don’t need much discussion about that.
Looking for suggestions as to what is a good but thin insulation to use.
Also I know this will last a long time but what’s a good estimate 20 years?
I’ve heard wrapping it tight is better than loose and I’ve heard loose is better than tight, what’s AT’s opinion?
 
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Billb2

Diamond Member
Mar 25, 2005
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So you want to prevent the heat/cool air in the ducts from leaking...... into your house?

Why? It's going there anyway!
 
Feb 4, 2009
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Old furnace and beginning run these are tight to the ceiling. I’m intimidated by this part

VMdisjo.jpg

More:
Whole square run is about 40’
93pHEso.jpg


Between the two square runs is tight about an inch or two

YmiZQ0k.jpg

Feed line about 2” of clearence to ceiling

LVf5KWX.jpg


Another round pipe to vent these are all pretty similar

0Lktnzj.jpg
 
Feb 4, 2009
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So you want to prevent the heat/cool air in the ducts from leaking...... into your house?

Why? It's going there anyway!

Run is in the basement, I live in MA. Pictures above

No duct work in the walls except a tiny bit in the bathroom (like 6 inches). Same with the air intake but I see no reason why that needs insulation. No duct work in the attic.
 
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Greenman

Lifer
Oct 15, 1999
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Spray foam is going to be the best method, and the most expensive. Fiberglass will do the job cheap, but it's going to be horrible to install. There are several different wraps available, some have very specific requirements, like an air space between the wrap and the pipe.
Don't ignore the air return, it should be insulated as well. Unless the basement is conditioned space, then none of this matters.
 
Feb 4, 2009
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Spray foam is going to be the best method, and the most expensive. Fiberglass will do the job cheap, but it's going to be horrible to install. There are several different wraps available, some have very specific requirements, like an air space between the wrap and the pipe.
Don't ignore the air return, it should be insulated as well. Unless the basement is conditioned space, then none of this matters.

This needs to be a DIY solution, I like spray foam but it sounds like I’d need a professional or at minimum professional equipment.
Why does the return need insulation?
 

Greenman

Lifer
Oct 15, 1999
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This needs to be a DIY solution, I like spray foam but it sounds like I’d need a professional or at minimum professional equipment.
Why does the return need insulation?
Because it radiates heat. Every place where the system looses energy should be insulated. Every leak in the duct work should be sealed.
I'm very surprised your floor isn't insulated, is the basement conditioned space? I'm guessing it isn't because the furnace isn't enclosed, but there has been some air sealing done, so someone may have sealed it. Where does the furnace get combustion air from?
 
Feb 4, 2009
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Because it radiates heat. Every place where the system looses energy should be insulated. Every leak in the duct work should be sealed.
I'm very surprised your floor isn't insulated, is the basement conditioned space? I'm guessing it isn't because the furnace isn't enclosed, but there has been some air sealing done, so someone may have sealed it. Where does the furnace get combustion air from?

I can do the intake that’s why I’m looking for opinions.
House was built in 1960, they simply didn’t insulate much back then.
I’ll have the floor done thru a Mass energy program that will get done, just might be next year with the appointment scheduling.
Basement is not conditioned space furnace intake is inside the house to my knowledge.
Previous sealing was from when we bought the house we added attic, wall and foundation sealing from the previously mentioned Mass energy program. Didn’t bother with the ducts because they are not part of the program and the furnace was 80% efficient at that time. We use a about 325-400 gallons of fuel per year so I never put much thought into the duct work. We are adding cooling so I think it’s a good point to re-evaluate duct insulation.
Furnace is getting replace because we’ve had 6 breakdowns in 2 years it’s about 30-32 years old.
Interesting thing about our house is it’s one of the first ones built, our floor joists are all 10 or 14 inches apart. There are only two that are the standard 16 inches. Our floor only creaks in one spot of the house. The flooring is very rigid. Only original owner left in the area said ours was used as a model house for a few years. I’ve wondered if we have the extra support to help sell the other units.

Intake picture:
I’d like to do something with this to tighten it but I’m not a very good carpenter

0QUJ9IH.jpg
 
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WilliamM2

Platinum Member
Jun 14, 2012
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You can get a thicker grill to hide those gaps in the flooring and hide the ends of the baseboard trim. It will flow more air as well:

https://www.amazon.com/White-Projection-Baseboard-Return-Grill/dp/B01MQQI4VI/ref=sr_1_2?ie=UTF8&qid=1533748269&sr=8-2&keywords=baseboard+air+return+grille&th=1

That's not the only return air grill is it? If so, it seems very undersized.

I wouldn't bother insulating/sealing ducts in the basement. Any lost energy just leaks into the house. You'll never notice the difference. In fact we have two heat register outlets in our unfinished basement. Keeps the floors from being so cold in the winter. And heat rises. We close them in the summer for cooling season, basement is already cool and dry.

I've seen fiberglass insulation get soaked from condensation from the ducts when running AC as well.
 
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Feb 4, 2009
35,672
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You can get a thicker grill to hide those gaps in the flooring and hide the ends of the baseboard trim. It will flow more air as well:

https://www.amazon.com/White-Projection-Baseboard-Return-Grill/dp/B01MQQI4VI/ref=sr_1_2?ie=UTF8&qid=1533748269&sr=8-2&keywords=baseboard+air+return+grille&th=1

That's not the only return air grill is it? If so, it seems very undersized.

I wouldn't bother insulating/sealing ducts in the basement. Any lost energy just leaks into the house. You'll never notice the difference. In fact we have two heat register outlets in our unfinished basement. Keeps the floors from being so cold in the winter. And heat rises. We close them in the summer for cooling season, basement is already cool and dry.

I've seen fiberglass insulation get soaked from condensation from the ducts when running AC as well.

Clever idea on that vent, problem is it’s 30” if I remember correctly. This was a previous project that I gave up on.
 

Red Squirrel

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The simplest might be to wrap in some roxul insulation all around the big trunk lines, then build a bulk head to hold it all in place.

But honestly I would not really bother. If you have major air leaks, fix those first. Also no sense in insulating the return, it does not really matter if there is loss, since that air is just going back to be heated anyway. Generally the air in the return is going to be room temperature, so the loss rate is going to be very small as there will hardly be any temp difference between the inside of the duct and the outside of it.

You need to heat the basement anyway, so the radiating heat from the ductwork will do that. Close off a couple basement vents if you need more airflow and let the ductwork handle the rest. Make sure you have at least one vent and one return in the basement though just to make sure you have some basic air circulation.

If you're still wanting to do this I would only do the main supply trunk, there is really no point in doing the return.
 

WilliamM2

Platinum Member
Jun 14, 2012
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Clever idea on that vent, problem is it’s 30” if I remember correctly. This was a previous project that I gave up on.

There are several sizes available, including 30"x6" and 30"x8". Not really sure I would classify that as a project, it's just two screws. I changed all mine when we painted because they were beige colored from the 70's.

https://www.amazon.com/White-Projec...8-2&keywords=baseboard+air+return+grille&th=1

Is that the only return vent? If it is you have bigger issues.
 
Feb 4, 2009
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There are several sizes available, including 30"x6" and 30"x8". Not really sure I would classify that as a project, it's just two screws. I changed all mine when we painted because they were beige colored from the 70's.

https://www.amazon.com/White-Projection-Baseboard-Return-Grill/dp/B01MTV20MN/ref=sr_1_2?ie=UTF8&qid=1533748269&sr=8-2&keywords=baseboard+air+return+grille&th=1

Is that the only return vent? If it is you have bigger issues.

Second one on the other side of that half wall.
The wood it screws into is all messed up, just a frustrating project that I don’t like.
I did see the larger sizes and I think you have a good idea.
 

Greenman

Lifer
Oct 15, 1999
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So is the consensus just seal the ducts but not bother insulating?
Not necessarily. The furnace has to be drawing combustion air out of the basement, so the basement has be ventilated. The next question is, how cold does it get in there in the winter? The greater the delta between the ducts and ambient, the greater the heat loss. It's the same for the return air, if the air drops 3 degrees running through an uninstalled duct, that's 3 degrees more heat the furnace has to supply.
If the furnace is keeping the basement warm in the winter, that's wasted heat. It would be pretty easy to figure out how many BTU's it's using. Your best bet would be to ask the guy who does the furnace, he's familiar with the area and he can actually see whats happening on site.
FYI, I'm a building contractor and BPI certified.
 
Feb 4, 2009
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Not necessarily. The furnace has to be drawing combustion air out of the basement, so the basement has be ventilated. The next question is, how cold does it get in there in the winter? The greater the delta between the ducts and ambient, the greater the heat loss. It's the same for the return air, if the air drops 3 degrees running through an uninstalled duct, that's 3 degrees more heat the furnace has to supply.
If the furnace is keeping the basement warm in the winter, that's wasted heat. It would be pretty easy to figure out how many BTU's it's using. Your best bet would be to ask the guy who does the furnace, he's familiar with the area and he can actually see whats happening on site.
FYI, I'm a building contractor and BPI certified.

Nice suggestion thank you. Basement is cool in the Winter apx 60 degrees. We keep the house 66-68 when occupied

Thing about the guy doing it, he once said to me.
I started my apprenticeship installing in this neighborhood
When I started my company in the 80s I replaced a bunch of the heaters in this neighborhood
Now I’m supervising apprentices cleaning the furnaces in this neighborhood

*he was with guy do my yearly service. Took hours but it was so wonderful hearing an experienced guy transferring knowledge
 

Red Squirrel

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Not necessarily. The furnace has to be drawing combustion air out of the basement, so the basement has be ventilated. The next question is, how cold does it get in there in the winter? The greater the delta between the ducts and ambient, the greater the heat loss. It's the same for the return air, if the air drops 3 degrees running through an uninstalled duct, that's 3 degrees more heat the furnace has to supply.
If the furnace is keeping the basement warm in the winter, that's wasted heat. It would be pretty easy to figure out how many BTU's it's using. Your best bet would be to ask the guy who does the furnace, he's familiar with the area and he can actually see whats happening on site.
FYI, I'm a building contractor and BPI certified.

Don't furnaces manufactured after like the 80's have a combustion intake? They are a closed system. It's one of the things that makes them so efficient as they arn't creating a vacuum and causing cold air to enter the house. That and the heat exchangers are much more efficient too, it's why they can get away with ABS or PVC for the exhaust. I suppose it would be worth insulating both of those pipes though, because the part of the wall they penetrate in will create a heat loss as the wall of the pipe does not have that great of a R value and will introduce a heat loss when the furnace is not running. Though considering the furnace is going to be running most of the time anyway not sure how much of a difference it makes. One of the pipes will always be a big warm while the other will be very cold. You could insulate the cold (intake) one all the way to the furnace I suppose.
 

Billb2

Diamond Member
Mar 25, 2005
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This isn't tape for ducts, it's just called duct tape.
S-6519.jpg


This is tape for ducts. It's aluminum, stays in place, and lasts forever.
JVCC-AF20-All-Weather-Foil-Tape-250.jpg

You might want to look into a back draft regulator for the furnace exhaust.
There are passive (bi-metalic or counterweight) and active (electrically controlled) ones.

Barometric Damper (Draft Regulator) on Oil-fired Appliances.
http://www.ashireporter.org/HomeIns...Draft-Regulator-on-Oil-fired-Appliances/14934
 
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Red Squirrel

No Lifer
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^

That's correct. I always laugh when I see duct tape in the duct section at Home Depot. So many people are misled by this lol. Duct tape was originally called duck tape, and was used in military applications to waterproof things in a pinch, like boots or ammo cases.
 
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I have one of those, it’s behind the green piece in the first picture. Scale is screwy in that picture, the furnace is not against the wall.
I had a discussion with the furnace guy yesterday about moving the heat pump location wife didn’t like the proposed site. I asked about insulating the ducts he said a quote from him would be embarrassing because of the labor he didn’t think it was a bad idea assuming I’m okay doing it myself.
I think my modified plan will be to wait until the floor gets insulated then reevaluate where we are at. We don’t use much oil with our current inefficient furnace, I’d assume we’ll use less with a newer higher efficiency one.
I’m a little concerned about cooling the basement in the summer but again without at least trying it out it’s hard to compare.
I absolutely will seal the ducts, I know about cleaning them so the tape or mastic crap sticks to them. Good fall project that can be handled in small chunks.
 

Red Squirrel

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If you don't have a high efficiency furnace it pays to swap it for a 90%+ high efficiency one. It will pay for itself in a few years. I think they actually go up to 98% efficient now, it's pretty crazy. I sometimes ponder on switching mine out for a 98% and then putting the 90 in the garage when I insulate/condition it, though that would probably be way overkill for the garage.
 
Feb 4, 2009
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If you don't have a high efficiency furnace it pays to swap it for a 90%+ high efficiency one. It will pay for itself in a few years. I think they actually go up to 98% efficient now, it's pretty crazy. I sometimes ponder on switching mine out for a 98% and then putting the 90 in the garage when I insulate/condition it, though that would probably be way overkill for the garage.

Can’t remember the exact efficiency on the one that’s coming but it’s good, there was something weird about the air intake for the super high oil ones.
My plan is ideally keep the house a more consistent tempature. We have solar we run $300-500 yearly credit so electric for the heat pump shouldn’t be much of an issue. I figure if that can get us to mid December then take over again in late March that’s not a huge window of oil use. Summertime we’d just like to keep the house around 80 when not home for the pets 74ish when we are home.
 

Greenman

Lifer
Oct 15, 1999
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Can’t remember the exact efficiency on the one that’s coming but it’s good, there was something weird about the air intake for the super high oil ones.
My plan is ideally keep the house a more consistent tempature. We have solar we run $300-500 yearly credit so electric for the heat pump shouldn’t be much of an issue. I figure if that can get us to mid December then take over again in late March that’s not a huge window of oil use. Summertime we’d just like to keep the house around 80 when not home for the pets 74ish when we are home.
Wait a sec here! Pets get just as hot as you do. Step up to the plate and keep them comfortable.
 
Feb 4, 2009
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Wait a sec here! Pets get just as hot as you do. Step up to the plate and keep them comfortable.

We’ve had nothing but fans for all their lives except the oldest cat may remember ac from the apartment.
 
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