Poor duct layout, best alternative?

[PCustoms]

So I've got a basketcase forced hot air system....

Vertical off the top of the furnace, "T" into the 8x16 main trunk. ~30' one way and maybe 6' the other.

On the short side, there is a 6" branch off to the bathroom register, then a foot later another 6" duct right where the main trunk ends.

This 6" branch goes ~3', 90° into ~14', another 90° for about 6' to a floor register and then necks down to 4" for about 8' to the final register.

Without tearing the whole system out (I've thought about it) is there a better way to run this?

 

[PCustoms]

 

[fitter30]

Brand and model of furnace and if it has ac ? Need tonage and is the evap coil in a matching coil cabinet. Some pics would help. Adding dampers would help in the round pipe.

Master Flow 6 in. Damper D-6 - The Home Depot

Master Flow - 6 in. Damper - Used to adjust the air flow in individual runs of round pipe in HVAC systems. Constructed of galvanized steel. - THD SKU# 149357

www.homedepot.com

 

[PCustoms]

Brand and model of furnace and if it has ac ? Need tonage and is the evap coil in a matching coil cabinet. Some pics would help. Adding dampers would help in the round pipe.

Master Flow 6 in. Damper D-6 - The Home Depot

Master Flow - 6 in. Damper - Used to adjust the air flow in individual runs of round pipe in HVAC systems. Constructed of galvanized steel. - THD SKU# 149357

www.homedepot.com

No AC

Why does brand/model matter for the furnace?

Just looking for a more efficient layout.

Why dampers, what problem does that solve? Registers have dampers

 

[mm08822]

Come straight out of the end of the 8x16 with the 6" diam. This eliminates one 90.

This let's you reuse all existing ductwork and dispose of one 90.

Kinda guesswork w/o pics.

 

[PCustoms]

Come straight out of the end of the 8x16 with the 6" diam. This eliminates one 90.

This let's you reuse all existing ductwork and dispose of one 90.

Kinda guesswork w/o pics.

Pic won't show anything more then my sketch. Probably less as I won't be able to step back enough for a good shot...

Your suggestion was my first thought. Downside would be having a low spot in the basement ceiling there.

My other idea was to come off the trunk on the other side, then run it along the beam and make a "T" at the end. Just as inefficient, but overall maybe cleaner.

 

[mm08822]

A few options for certain, but w/o any real objective or future use purpose, it's anybodie's guess.

 

[mike93lx]

Is this rigid or flex duct?

 

[PCustoms]

Is this rigid or flex duct?

Rigid

 

[PCustoms]

A few options for certain, but w/o any real objective or future use purpose, it's anybodie's guess.

It's my basement/drive out garage. Previous owner routed the extra 90's to get it over to the wall to clear the GDO (and cut the joists, but that's another thread).

I want to get the buttoned up as the joints leak like crazy and I'll be putting drywall on ceiling this winter.

Realistically when the furnace shuts the bed I'll probably go a different direction. Not a fan (pun!) of forced hot air...

 

[danski0224]

Come straight out of the end of the 8x16 with the 6" diam.

Not good.

 

[danski0224]

This 6" branch goes ~3', 90° into ~14', another 90° for about 6' to a floor register and then necks down to 4" for about 8' to the final register.

If there's any way to use adjustable elbows and make them less than 90* by turning the sections, then do it.

 

[fitter30]

No AC

Why does brand/model matter for the furnace?

Just looking for a more efficient layout.

Why dampers, what problem does that solve? Registers have dampers

Size of furnace and ac will tell how many cfm needed. Will also tell if the duct both supply and return if their large enough. Evap coil in cabinet tells me if its matched to the furnace. Pics that i can see if the duct is even installed correctly.

 

[mm08822]

Not good.

Why, how so different than what OP has now? For sure a lot of turbulence w/o transitioning to the circular cross-section.

 

[fitter30]

Size of furnace and ac will tell how many cfm needed. Will also tell if the duct both supply and return if their large enough. Evap coil in cabinet tells me if its matched to the furnace. Pics that i can see if the duct is even installed correctl

You cannot balance a duct system at the registers. The dampers work because if you close them, they increase trunk pressure and feed the other outlets.
If you feel your short of air or seems like when furnaxw was newer had more air look at the blower wheel and if the blades have even a small.amount of dirt on them the blower needs to be pulled and cleaned.

 

[Bert_]

What problems do you have that you are trying to solve?

 

[PCustoms]

Pics that i can see if the duct is even installed correctly.

It's so far from correct it's not even funny.

The return duct was split between the the stairwell and pulling in basement/garage air. The duct was a mixture of sizes and styles, none of it correctly installed or sealed.

The furnace isn't original. It's got some hokey adapter made with aluminum angle from the hardware store.

My primary heat is the wood stove (plenty of free wood). I use the blower to circulate the air and for when I travel.

Goal here is to improve the section of duct, if possible, before I finish the ceiling. Sounds like using some logic with the 90's is the best I'll be able to do.

 

[danski0224]

Why, how so different than what OP has now? For sure a lot of turbulence w/o transitioning to the circular cross-section.

Doesn't allow pressure to build up in the ductwork.

Actually supposed to stay a couple of duct diameters away from the endcap.

 

[PCustoms]

Would changing the duct to follow the red line be any improvement?



It would neaten up the ceiling space...

 

[PCustoms]

Would changing the duct to follow the red line be any improvement?



It would neaten up the ceiling space...

Bump.

Any improvement (or harm) re-routing the 6" duct along the red line, into a tee to feed the 2 registers on the right side of my sketch?

 

[danski0224]

Honestly, your diagram ***** and it makes no sense. It looks like a mish mash of plan and elevation views.

If you don't want to tear out the system and redo it (first post, last sentence), then what does it matter what is done? It certainly won't get "fixed" "later" after you finish the ceiling (post #17).

As mentioned before, if there are back-to-back 90º elbows installed where there is an elevation change, then "opening" or "adjusting" even one of them to a 45º elbow and doing a rolling offset would do wonders.

 

[PCustoms]

Honestly, your diagram ***** and it makes no sense. It looks like a mish mash of plan and elevation views.

It's too down view, no elevation changes are implied. I can re-draw it if that somehow helps you answer what should be a basic question

If you don't want to tear out the system and redo it (first post, last sentence), then what does it matter what is done? It certainly won't get "fixed" "later" after you finish the ceiling (post #17).

I'm not tearing it out as there's 40' and 7 or 8 floor registers in the other direction that are already insulated and boxed in where they aren't causing headroom issues. When the furnace shuts the bed I'll likely abandon forces hot air

As mentioned before, if there are back-to-back 90º elbows installed where there is an elevation change, then "opening" or "adjusting" even one of them to a 45º elbow and doing a rolling offset would do wonders.

There's no back to back elbows, not sure how you thought there was. The only elevation change (not shown as it's not relevant to my question and would be the same no matter which path I take) is already rolled 45's.

The issue is simple previous owner ran additional duct to get over to the exterior wall and then looped back around for the final 2 floor registers as he needed headroom (also cut floor joists!) for a door opener. I fixed the existing path, replaced a mismatch of ductwork and sealed the joints after I spent $3k in propane and still froze the first year I was here.

Before I add more insulation and drywall the ceiling downstairs I want to box in the balance of the duct (and some plumbing), running it in a chase along the beam would be easier and less obvious, but I'm not going to move it if having the "tee" feed the last 2 registers is a bad idea. The rest of the red path would be better essentially the same distance, just flipped to the opposite side of the trunk.

 

[danski0224]

It's too down view, no elevation changes are implied. I can re-draw it if that somehow helps you answer what should be a basic question

Well, then it should have been labeled "plan view". There is probably some bias in how I would look at it, as drawn, because it looks like a horizontal trunk line with the takeoff coming off the top, up into the floor joist, then coming down. I have seen people draw like this, and it really isn't right, either.

There is (probably) no difference in whether the 6" comes off of one side or another.

Not seeing (or really interested in seeing) the rest of the ductwork, it is hard to say what could be done, but you have made it clear that nothing will be done, so it doesn't matter, right?

Most of your problem is propane.

1,000 cubic feet of natural gas = 1 million BTUs
11.2 gallons of propane = 1 million BTUs

Natural gas in my area is something like $.25 per therm (100,000 btu), so do the math.

It would probably be cheaper for you to put in something like a Bosch ultra low temp heat pump (if 60k btu is enough heat) if natural gas is not available in your area.

Chasing duct insulation and stuff like that is small potatoes. You need a blower door test to find the holes, and plug them.

 

[danski0224]

Before I add more insulation and drywall the ceiling downstairs

This is pointless if the "downstairs" is also part of the area defined as conditioned space.

The void between the first and second floor isn't insulated (but the rim joist should be).

You need to define what is "conditioned space", and then make the thermal envelope match.

If "downstairs" is a garage (the door opener comment), then it is especially vital to properly define the thermal boundary between "inside" and "outside". I have NEVER seen a "bonus room" floor above a garage that was properly insulated.

 

[PCustoms]

Not seeing (or really interested in seeing) the rest of the ductwork, it is hard to say what could be done, but you have made it clear that nothing will be done, so it doesn't matter, right?

Rest of the ductwork isn't currently an issue.

Most of your problem is propane.

1,000 cubic feet of natural gas = 1 million BTUs
11.2 gallons of propane = 1 million BTUs

Natural gas in my area is something like $.25 per therm (100,000 btu), so do the math.

It would probably be cheaper for you to put in something like a Bosch ultra low temp heat pump (if 60k btu is enough heat) if natural gas is not available in your area.

No natural gas here but thanks for the lessons in math.

I don't use much propane anymore, primary heat is wood. Furnace only kicks on if I'm out for a bit and didn't feed stove, or on shoulder seasons where the stove would cook me out.

The 35k mini split is fine for shoulder seasons now

Chasing duct insulation and stuff like that is small potatoes. You need a blower door test to find the holes, and plug them.

I try to limit the extraneous details when posting like this as people misconstrue information to fit their narrative. I didn't chase "duct insulation and stuff like that" I fixed gaping holes in ductwork from poor install and intentional holes from someone trying to heat the leaky basement garage.

It also wasn't relevant to the original post that I had a baseline blower door test in 2018 prior to spray foaming most of the house, with additional blown in to bulk the attic well past recommend values. They came back and did a second test (part of the energy audit)!once the work was done. The house was tight then, and I've only made it tighter since.

Air sealing and discussing my various options for generating heat was not the purpose of this thread.

 

[PCustoms]

This is pointless if the "downstairs" is also part of the area defined as conditioned space.

The void between the first and second floor isn't insulated (but the rim joist should be).

You need to define what is "conditioned space", and then make the thermal envelope match.

If "downstairs" is a garage (the door opener comment), then it is especially vital to properly define the thermal boundary between "inside" and "outside". I have NEVER seen a "bonus room" floor above a garage that was properly insulated.

We're off in the weeds now with things that don't relate to duct routing and have already been resolved since I've owned the house.

Thanks for trying to help