HVAC dilemma

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EbS-P

Minister of Fire
Jan 19, 2019
2,705
SE North Carolina
Background we have a 3 ton 16 seer package unit ( it’s probably too small now) that has never heated the house well when it’s cold. The previous own left behind 4 space heaters when we bought the house. (i believe she one spent one winter in the house with the new heatpump. )
Fast forward 7 years. We had a cold spell could not get the house much above 60 for a 36 hours. Fast forward 8 we added a wood stove and it we use it for 70-80% of our heating needs. Fast forward 10 years. We renovated the two car garage in the walkout basement to living space adding 500 more square ft. Added an insert downstairs.
Yesterday was look around with my thermal camera I decided to venture into the crawl space again. I’ve been in many times. Ducts are very leaky. Access to them is terrible. Getting down on my stomach I finally get eyes look on my return duct. It’s completely un-insulated. Call it 25’ of rectangular galvanized duct running through a vented crawl space. Appears 90% of the ducting is original to when the house was built in 1965. Insulation that’s present isn’t good.
There is about a 12” gap to crawl under the the supply duct to get to the return duct.
Outside temps were high teens the other night and the temp inside the crawl space dropped to 43. Any insulation has fallen off the subfloor down there. Humidity regularly exceeds 80% in the summer in the crawl space (but the leaky ducts can usually drop it down a few points. I have graph if you want to see them.
Consequently I can heat the crawl space faster than my bedroom. (For the first 45 minutes) When it’s colder than 25 I don’t get any temperature difference between return and supply air. I just shut the system off or run only 10kw resistive strips.
So what’s a person to do?

1-nothing. It’s been that way for 12 years. Address it when the heatpump needs replaced.

2- try to DIY insulate the return and seal and insulate the supply ducting.

3- pay have all duct work replaced and up sizing for a future 4-5 ton heatpump.

4 - install a mini split head or secondary complete unit upstairs (basement will get its own mini split at some point I. The next 18 months.

5-something else???

I know the right thing is to take everything out, insulation, ducts, scraps of plastic that only look like a vapor barrier, and start over with new, insulation, vapor barrier ducts (conditioned crawl space?) ect. I really don’t want to spend 10-20k$ in/on a crawl space but feel I need to do something.
Thanks for your thoughts
Evan.
 

EatenByLimestone

Minister of Fire
It sounds like its not a very high crawl space. Is the ground concrete or soil?


I'd look hard at insulating the crawl and sealing the moisture out. Membrane on the bottom and closed cell foam on the walls.
 

EbS-P

Minister of Fire
Jan 19, 2019
2,705
SE North Carolina
It sounds like its not a very high crawl space. Is the ground concrete or soil?


I'd look hard at insulating the crawl and sealing the moisture out. Membrane on the bottom and closed cell foam on the walls.
It’s all sand. Think beach sand. It’s not very high for most of it 30” or less. Higher at the access door.

There is a possible issue with encapsulating and insulating it. Right now we are in a flood zone (map was drawn incorrectly but it was easier and cheaper not to challenge map will be corrected when a drainage project is completed ). Flood insurance is written with a vented crawl space.
 

Max W

Member
Feb 4, 2021
109
Maine
Sounds like you’re not going to be satisfied spending money rehabbing, re insulating the ductwork system. I would be tempted to clear it all out, lay down that membrane, insulate well under the floor (spray foam if termites or ants weren’t a concern and wood was dry) make sure the space is very well vented and go with the split head and full mini split and of course your stove and insert.
 

EbS-P

Minister of Fire
Jan 19, 2019
2,705
SE North Carolina
So after giving it some thought I want to insulate and air seal the ducts in some manner. The supply has some insulation but is needs sealed.

How would you insulate the return. I can probably dig out 12” under supply duct to move materials.
 

EatenByLimestone

Minister of Fire
Easiest would be a foam spray. There are good homeowner packs available that will let you apply it yourself. Wear a good respirator and a tyvek suit.
 
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RockyMtnGriz

Burning Hunk
Apr 19, 2019
166
SW Montana
Off the wall, and probably useless suggestion, but if it's beach sand, could you use a vacuum unit to easily increase the space you have to work with?
 
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Bad LP

Minister of Fire
Nov 28, 2014
2,001
Northern Maine
Off the wall, and probably useless suggestion, but if it's beach sand, could you use a vacuum unit to easily increase the space you have to work with?
You’d be shocked what a vacuum excavation machine can do. Look at Ditch Witch.
 

EbS-P

Minister of Fire
Jan 19, 2019
2,705
SE North Carolina
Easiest would be a foam spray. There are good homeowner packs available that will let you apply it yourself. Wear a good respirator and a tyvek suit.
Spraying the top which is touching joists and the then the bottom would be difficult. I like the idea.

My solution was to tape seal and then secure insulation batts as best I could maybe even wrapping with the packing plastic wrap. I thought about cutting and glueing foam board too.

It just cutting the whole duct out an replacing with insulated flex duct. The return makes a vertical 90 then immediately makes a 180 to line back up with the compressor unit. The return parallels the supply for about 15’. 6-12” between the two.
 

gzecc

Minister of Fire
Sep 24, 2008
4,948
NNJ
I would consider replacing it or adding R10 2" foam board to the exterior after you seal any leaks. Screw to the existing duct.
Crawl spaces get little love. Be careful with plastic/ moisture barriers. You don't want to trap moisture.
 

EbS-P

Minister of Fire
Jan 19, 2019
2,705
SE North Carolina
I also think that the best approach is to use foam!
Can you imagine what the next owner of the home or repairman says when he sees my handy work. First time spraying foam in a tight confined space. Thinking about the elephant foot

Wow just checked froth pack prices on Amazon. 2$ a board foot. That up from last time I looked by a lot.
 
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ABMax24

Minister of Fire
Sep 18, 2019
1,544
Grande Prairie, Alberta, Canada
Can you have a sheet metal trough built that hangs from the joist and would give say 3" of clearance around the duct, and then pour in some urethane foam for insulation? You could then put expanded foam sheet or spray foam on top of the duct to insulate that.

Pictures would be helpful to see what your duct looks like.
 

Highbeam

Minister of Fire
Dec 28, 2006
19,785
Mt. Rainier Foothills, WA
Remove and replace with insulated flex duct. It’s very difficult to air seal and insulate existing ductwork correctly with normal fiberglass and if you don’t get it perfect then the condensation will soak the rest with water. Mold, stink, ick.

The flex is cheap and only slightly more restrictive than metal.
 
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EbS-P

Minister of Fire
Jan 19, 2019
2,705
SE North Carolina
Can you have a sheet metal trough built that hangs from the joist and would give say 3" of clearance around the duct, and then pour in some urethane foam for insulation? You could then put expanded foam sheet or spray foam on top of the duct to insulate that.

Pictures would be helpful to see what your duct looks like.
Here they are. Supply is closest. It’s tight . The 4’ closest to the compressor are insulated. Second pic shows the quality of they insulation on the supply duct.

7A7B9AC3-C1EB-436F-9A54-DCC8A779BD60.jpeg 47A27BD3-F8EE-4A01-A9C6-4347E41FDB52.jpeg
 

vbu

Member
Mar 3, 2019
92
MS
Are you sure the square ducting is not insulated on the inside? That's how it is at my house, built in '68
 

EbS-P

Minister of Fire
Jan 19, 2019
2,705
SE North Carolina
Are you sure the square ducting is not insulated on the inside? That's how it is at my house, built in '68
I know the U turn is not insulated it’s the only part I could touch.

It’s such a mess down there. Flowers are coming up it made it through another heating seasoning. I’m not worried about cooking. I looked the highest dew point I measured during the summer was still well above indoor temp setting. So I’m not worried about Condensation in the return. Leaky ducts help keep it dry in the summer. I will be sealing my vents well this spring as a test to see how dry it stays. When the blower goes to high you can feel cold air exiting the the crawl space vents. If the humidity gets bad I have an outlet for a dehumidifier.

The wiring is a bit of a mess and of course all the basement wiring and 240v runs are just laying on top of the supply. None of the water pipes are insulated down there.

The reality is if I’m not ready to rip it all out, anything else is a band aid. If I want to put in a bigger heatpump it’s all under sized and will need to be replaced and a basement return added. If I can keep it dry I’m in good enough shape I guess. I could easily drop $8,000 and probably not get more than 15-20% improvements in efficiency. A diy mini split is 1/4 of that, more efficient and allows some zone zoned temp control.

I get all these ideas that I need to do something, but not doing anything is sometimes the right call.
 

mcdougy

Minister of Fire
Apr 15, 2014
794
ontario
Why not perimeter seal and insulate the wall and vapour barrier and insulate the dirt. Closing of the vents as well to make a conditioned space. Moving forward with new heatpumps and duct would make this approach good money spent?? It's a common solution to.damp. unappealing crawl spaces around here. I agree that trying to insulate and repair the ducts would be good money on a bad solution...
 

rwhite

Minister of Fire
Nov 8, 2011
1,887
North Central Idaho
What are the dimensions of the ducts? Any chance a round insulated flex duct can be fished through the square duct?