Flex-Duct Sizing/Installation

[Social_Joe]

The trials of installing central heat (was titled:Flex-Duct Sizing/Installation)

I'm looking for some input on proper sizing and distribution for a flex duct system running from a pre-fab plenum.

http://www.homedepot.com/h_d1/N-5yc...=10053&langId=-1&keyword=plenum&storeId=10051

Building is approximately 30x40 with a 8x8 enclosed bathroom and 4x5 enclosed doghouse I want to run a duct to as well. Building is approx 10' to the eaves, 16' to peak. AHU is a 3.5 ton Payne Electric.

I'm fairly newb to duct sizing, should I run one main flex as a trunk and sprout vents off of it using wyes? There currently is no ceiling, but I may eventually add one.

I'll be glad to provide any additional information needed.


Thanks in advance.

 

[Social_Joe]

The yard is mowed now...

As of yesterday

Right after closing

Restroom is in the center of this pic

This is my "doghouse" in the middle of framing. It's in the SW corner of the building. I want to run a duct to it as well. The door leading to the outside will have a rubber flap (old floormat) to keep as much heat in as possible. In summer I plan to put a 5000k window unit (already own) it in so I don't have to cool the shop to keep the dogs comfy (it gets HOT here).

 

[pseudorealityx]

Where's the unit located?

 

[Social_Joe]

Thanks for the reply, I've been reading this thread: http://garagejournal.com/forum/showthread.php?t=101072&highlight=flex+duct


--
Right now it's on the (back) north wall (wall parallel with the back fence). Obviously it can be moved and I need to build a base/intake plenum yet. I put it over there because the plumbing and bathroom is in the N/E corner. The electrical panel is on the south wall.

So I guess in reality the unit could be moved just about anywhere, but I'd like to keep it on the north wall so when I add a/c later the copper lines can be short. I intend to enclose that 1/2 car-port corner soon.

 

[DPelletier]

1) I don't like rigid fiberglass board ductwork (micro-aire looks to be a similar product). It isn't particularly strong, especially at the joints and it is difficult to install an AC coil in properly. In addition, the fibres usually end up in the supply air stream which in turn deposits it in your shop and in your lungs....sorry, not a fan.

2) my advice would be to have a local sheet metal shop fab up a plenum to match your unit. I would also build the plenum to suit the later installation of the Evap coil.

3) flex duct is easy to install but far more restrictive than smooth metal ductwork. I would run one trunk line from the furnace below the trusses (so it's within the conditioned space and doesn't need insulation) and then put 6 or 8 takeoffs with double deflection registers on a 30 or 45 deg down angle.

I can size the duct you need to use if you give me the unit information.


Dave

 

[DPelletier]

in simple terms, a unit capable of supporting enough airflow for a 3.5 ton AC unit needs to have a capacity of around 1400 CFM. One round trunk line would need to be 16" round at a recommended residential static pressure of 0.10".

Ignore what I said about making the plenum big enough for your coil; it's already installed...BTW, are you sure that isn't a downflow (counterflow) unit? I see very few draw-through AC coils.

Dave

 

[Social_Joe]

Thanks for the info. I'm actually an architect by training (please be nice contractors, carpenters, etc.... I've actually done real construction in my life) , but don't have that much recent/practical mechanical sizing design background. I can draw up a FP to assist with layout.

Logical with having the plenum shop-built. How would that be dimensioned? So from the plenum, run a 16" trunk with 6-8 take-off's. What would you size those at? I'd wanted to run the trunk up in the rafters so I could have a finished ceiling later and maintain the height clearance. Admittedly, keeping it below them would save me from having to insulate it later if I did install a ceiling. I do like the visual aesthetic of exposed round ductwork and the liklihood of me installing a ceiling in the next 5-10 years is pretty low.

The unit is an updraft with the a-coil at bottom.

Here's it's info tag, thanks again for the assistance. I actually sized ductwork using a ductulator for my teacher in jr. high years ago, lol. He moonlighted as a HVAC tech and figured I was learning, ha.

 

[Social_Joe]

BTW,

The fan is set to middle speed and the AHU can be run with two coils or all three coils on. It's breakered at 120 at the unit (two 60 amp breakers, one catches two coils and the blower, the other just has one coil on it). I have it running through 6/3 wiring to a dual 70 amp breaker on a 150 amp panel. Running all three coils, it barely pulls over 100amps.

 

[Highbeam]

Scirroco. I had a 1980 or 1981 model with mech fuel injection. I swapped in a 1.8 from a GTI.

Nothing to add, just like the car.

 

[DPelletier]

Arrrrrg! Just spent ten minutes typing out a reply and lost it...

anyhow; the short version

- I'm not familiar with Payne products but the 043 part number probably corresponds to 43,000 BTUH or approximately 3.5 tons.

- always size the duct for the cooling load and requirements, not heating as the cooling will require more airflow.

- you can play with the number and sizes of outlets, but I'd go with 8 at 12"x 6" double deflection registers.

- you could put the duct in the attic but yes, then when you sheet it off and insulate the attic, you'd need to insulate the duct using 1" thermal duct insulation with vapor barrier.

...ps. some of my best friends are architects and some are even lawyers, so I won't hold it against you! haha!

Cheers,
Dave

 

[DPelletier]

Oh, and also if you put the duct in the attic, you will need to duct down below the ceiling with diffusers or something a little more extensive than an exposed spiral run with takeoffs.

Dave

 

[JimL]

You need 2 #6 circuits or at minimum a #6 and a #10. 60 and a 30 amp. Piggy backing a 15kw heater is fine, if the wire is big enough. 6 is not.

 

[Social_Joe]

Scirroco. I had a 1980 or 1981 model with mech fuel injection. I swapped in a 1.8 from a GTI.

Nothing to add, just like the car.

Thanks. It's my favorite toy. I need to fix the idiotic and now missing a/c tensioner assembly. I've put ALOT of love into that weird old German wedge.

Arrrrrg! Just spent ten minutes typing out a reply and lost it...

anyhow; the short version

- I'm not familiar with Payne products but the 043 part number probably corresponds to 43,000 BTUH or approximately 3.5 tons.

- always size the duct for the cooling load and requirements, not heating as the cooling will require more airflow.

- you can play with the number and sizes of outlets, but I'd go with 8 at 12"x 6" double deflection registers.

- you could put the duct in the attic but yes, then when you sheet it off and insulate the attic, you'd need to insulate the duct using 1" thermal duct insulation with vapor barrier.

...ps. some of my best friends are architects and some are even lawyers, so I won't hold it against you! haha!

Cheers,
Dave

Thanks!

Oh, and also if you put the duct in the attic, you will need to duct down below the ceiling with diffusers or something a little more extensive than an exposed spiral run with takeoffs.

Dave

Ok, now I see what you're getting at. I single duct/trunk run with vents directly off of it. Would you think 16" would be adequate and then could I run a single line off that to my doghouse (understand that it wouldn't be part of the return air).

Any idea on what I should be looking at price wise for the trunk (running the length of the shop) + plenum + registers?

You need 2 #6 circuits or at minimum a #6 and a #10. 60 and a 30 amp. Piggy backing a 15kw heater is fine, if the wire is big enough. 6 is not.

I have two #6 feeds and a #6 neutral. The two feeds go to two legs on a double breaker rated at 70 on each leg. Am I ok or do I need to up/double my neutral. I've done plenty of 110 work and thought I had this sized right/safe. Sorry if I appear ignorant, just want to be sure it's sized correctly.


Thanks to everyone for the help. I bought the heater intending to just put an elbow on the top for now... but that's silly. I might as well bite the bullet and get it done and have a heated shop. Really what pushed me over the edge was the doghouse. I want to heat it, but I don't want to leave space heaters or electric blankets inside a wood framed / sheathed small cube with my Great Dane and my Lab... sound like disaster in the making.

 

[JimL]

I have two #6 feeds and a #6 neutral. The two feeds go to two legs on a double breaker rated at 70 on each leg. Am I ok or do I need to up/double my neutral. I've done plenty of 110 work and thought I had this sized right/safe. Sorry if I appear ignorant, just want to be sure it's sized correctly.

Um, I don't think so.

Say I was building a new house and was telling my electrician what I need. I need a 60amp 230volt circuit and a 30amp 230volt circuit. Minimum a 6/2 with a ground for the 60 and a 10/2 with a ground on the 30. 2 pole 60 breaker and a 2 pole 30 breaker. 2 individual breakers. 4 slots in the panel.

Need 4 hots, and a ground.

 

[Social_Joe]

Um, I don't think so.

Say I was building a new house and was telling my electrician what I need. I need a 60amp 230volt circuit and a 30amp 230volt circuit. Minimum a 6/2 with a ground for the 60 and a 10/2 with a ground on the 30. 2 pole 60 breaker and a 2 pole 30 breaker. 2 individual breakers. 4 slots in the panel.

Need 4 hots, and a ground.

Ok. This was done under the supervision of a friend I trust. Perhaps his "redneck" engineering has gone too far.

Here's what the inside of the unit looks like. We have a single #6 run to each 60 amp breaker with a jumper to the 2nd leg. My understanding was that two coils+blower on one 60 and the third coil on the 2nd 60. So well under 120 total. That said, #6 is rated to 65 amps (@75deg C, 75 @ 90deg C) and each leg is on a 70 amp breaker back at the panel. So forgive my ignorance, but why wouldn't this be safe.

I understand your analogy, but if I wanted to wire a 60 amp 230v circuit... couldn't I run it on a single #6 off a 60 amp breaker, piggy back the unit breaker and be within the wire's capacity OR run two runs of 10awg to reach the same ampacity rating?

Feel free to flame me and call me names. I'm only putting this out here because I want my property and my life to be safe. For now I may just take the 2nd #6 hot and run it to the 60 that feeds the two coils+blower and not run coil #3 until I have my ducts setup. To get the margin of safety you're suggesting I'm going to need to run alot more copper, so I'll probably move the AHU to the southside of the garage near the panel instead of buying $150+ of wire.

 

[Social_Joe]

On 2nd review... I get it.... kinda. Wouldn't running 2 #6 hots to each breaker at the unit effectively double the needed amp rating of the wire?

Regardless. I'll unhook the 3rd coil (L3/L4) for now and probably move the unit closer to the panel so I can install 2 2-pole 60 amp breakers and run 4 #6 hots. I want it to be to code anyway. Am I ok staying with a #6 neutral and #6 ground or should I bump those up as well?

 

[JimL]

Your pulling 100 amps thru #6 wire and a 70amp breaker. That's alot.


You need a hot hooked to each of your line voltage lugs, L1-L4. Don't need a neutral, just a ground. 10ga is fine for a ground.

What you have now is hots coming in to L1 and L2, then a jumper from L1 to L3, and a jumper from L2 to L4? if so that is wrong.

 

[JimL]

$150 of wire is cheaper than a garage fire

 

[Social_Joe]

$150 of wire is cheaper than a garage fire

Absolutely true.

Jim,

Serious thanks for being patient with me and not just calling me an idiot and running away. It's really appreciated.

The AHU has a lug for neutral and a lug for ground, so I ran #6 neutral to that lug.

I have #6 run to L1 and L3 with a jumper from L1-L2 and L3-L4. Like I said for now I'll run both #6 wires to L1 and L2 and leave 3&4 empty for now.

So to do this right: #6 X 4 running to L1-L4 from two dual pole 60 amp breakers (two 30 amp breakers bridged for each pair of #6 feeds. Then at least a #10 ground. Why do I not need to run at least a #6 ground and/or neutral?

 

[DPelletier]

Any idea on what I should be looking at price wise for the trunk (running the length of the shop) + plenum + registers?



.

Your cost on materials only should be around $895.00 plus taxes. Prices may vary region to region a little and could go up or down depending on the type of registers you use. I would recommend 10' lengths of spiral pipe.

Yes, 16" pipe is large enough for 1400 CFM. I didn't include a cost for your dog house run or for a return air plenum or filter rack. I'd strongly recommend a filter so you don't plug up your AC evap coil.

Cheers,
Dave

 

[Social_Joe]

Your cost on materials only should be around $895.00 plus taxes. Prices may vary region to region a little and could go up or down depending on the type of registers you use. I would recommend 10' lengths of spiral pipe.

Yes, 16" pipe is large enough for 1400 CFM. I didn't include a cost for your dog house run or for a return air plenum or filter rack. I'd strongly recommend a filter so you don't plug up your AC evap coil.

Cheers,
Dave

Thanks for running the numbers

That's about dead-on to the qoutes I got from the supply house over lunch. That's a bit more than I'm looking to bite off right now. I may either run the trunk and just cut slots for the diffusers, but not install them yet or run two runs of 12" flex down either side of the shop with an equal number of registers. I know it's not ideal.

I keep wondering where I could come up with used barrels, pipe, etc to build a trunk out of for less than $106/10'.

I plan on building a base out of ply. The unit has a built in filter slot actually. I might put the filter in the an intake register in the plywood base though. To be seen.

 

[DPelletier]

No problem,

If I were you and the money was tight, I would install the plenum and enough pipe to discharge at the ceiling with a 90 degree elbow, If you still have some money, then install the horizontal 16" run with the takeoff holes cut and leave the takeoffs and outlets for later. That would save you around $300 for the takeoffs and registers. I've had issues trying to run electric furnaces without ductwork before.

The flex is a bad idea IMO; flex is very restrictive compared to rigid ductwork so two 12" runs is likely insufficient for 1400 CFM.

Another thought is to try around at any Commercial/Institutional Sheet Metal Shops or Mechanical Contracting firms (many of which do thier own sheet metal). You may get lucky and find one that is willing to sell you cutoff's or salvaged pipe at a deep discount. You could also try a scrap metal place.

Dave

 

[pseudorealityx]

Depending on the sheet metal place, rectangular may be cheaper. 16 x 14 would be ~equivalent to 16" round. At least worth a call.

If you want to do really cheap right now... locate the unit at one 'end' of the building, roughly centered. Have the ductwork go up, 90 degree to horizontal, and then put about 5' of duct (enough to pull a single small tap for the doghouse), and then size a diffuser to run at pretty high velocity (~1200 fpm). You'll be able to throw most of the length of ~30'. Downside is that you'll likely get some localized warm/cold spots, and it'll be louder. But you'll have a total of 10-15 ft of duct. Down the line, you could extend that trunk line the whole way, and then do take offs as desired.


EDIT: Seems like I was typing the same thing as the above.

 

[Social_Joe]

Depending on the sheet metal place, rectangular may be cheaper. 16 x 14 would be ~equivalent to 16" round. At least worth a call.

If you want to do really cheap right now... locate the unit at one 'end' of the building, roughly centered. Have the ductwork go up, 90 degree to horizontal, and then put about 5' of duct (enough to pull a single small tap for the doghouse), and then size a diffuser to run at pretty high velocity (~1200 fpm). You'll be able to throw most of the length of ~30'. Downside is that you'll likely get some localized warm/cold spots, and it'll be louder. But you'll have a total of 10-15 ft of duct. Down the line, you could extend that trunk line the whole way, and then do take offs as desired.


EDIT: Seems like I was typing the same thing as the above.

That's more doable right now and would allow me to add onto the trunk. I'd run 10' just for ease. What sort of diffuser would you fit that could run 1200fpm?

 

[JimL]

Absolutely true.

Jim,

Serious thanks for being patient with me and not just calling me an idiot and running away. It's really appreciated.

The AHU has a lug for neutral and a lug for ground, so I ran #6 neutral to that lug.

I have #6 run to L1 and L3 with a jumper from L1-L2 and L3-L4. Like I said for now I'll run both #6 wires to L1 and L2 and leave 3&4 empty for now.

So to do this right: #6 X 4 running to L1-L4 from two dual pole 60 amp breakers (two 30 amp breakers bridged for each pair of #6 feeds. Then at least a #10 ground. Why do I not need to run at least a #6 ground and/or neutral?

You lost me at "two 30 amp breakers bridged" ? You want a 2 pole 60. Exactly like whats in the heat pack. And a 2 pole 30. Making it more complicated than it is I have always used a #10 ground. Its what is bundled with 6/2.

Is the neutral just another ground lug? Should have 2 lugs, one on the case of the fan coil and one on the bracket that holds the breakers in. Use one for the ground and your done.

 

[Social_Joe]

You lost me at "two 30 amp breakers bridged" ? You want a 2 pole 60. Exactly like whats in the heat pack. And a 2 pole 30. Making it more complicated than it is I have always used a #10 ground. Its what is bundled with 6/2.

Is the neutral just another ground lug? Should have 2 lugs, one on the case of the fan coil and one on the bracket that holds the breakers in. Use one for the ground and your done.

Yeah, we're talking about the same breakers... I'm just using the wrong terms...

Yes, if you look at the photo I posted you'll see a lug off to the left side. That's where my neutral is running to. There's a second lug attached to the case that I'd assumed was for a ground. They both conduct to to the housing/case/etc. So both would be considered grounds.

My understanding had always been that the neutral needed to be of the same capacity as the hot in an AC system. And frankly I don't understand how having something running without a neutral, only a local ground, and a ground that's not of the same size is up to par/code. When I initially hooked it up I used the existing welder circuit, which was 6/2 with a 10 ground and I upped that to #6 to be safe.

So:
Dual Pole 60
Dual Pole 30
10AWG Ground

 

[Social_Joe]

After thinking about dryer and stove plugs... I got smarter...

www.nachi.org/forum/f19/220-no-neutral-question-rephrased-58367/

 

[JimL]

So... you are correct. L3 and L4 can be run in a #10 wire if you want. Make those 2 terminals your 30 amp breaker.

Don't need a neutral. I have put in a ton of fan coils and never had a neutral. Outside unit won't have one either.

Still trying to figure out how you got 100amps drawing when it was running! Should be closer to 60. Roughly 18 per bank and an amp or two for the fan.

 

[Social_Joe]

So... you are correct. L3 and L4 can be run in a #10 wire if you want. Make those 2 terminals your 30 amp breaker.

Don't need a neutral. I have put in a ton of fan coils and never had a neutral. Outside unit won't have one either.

Still trying to figure out how you got 100amps drawing when it was running! Should be closer to 60. Roughly 18 per bank and an amp or two for the fan.

Thanks. I'd much rather buy #10, but I'm moving the AHU closer to the panel due to duct routing anyway so I'll have plenty of #6..

How I "got 100 amps".... bonehead mistake on my part. When we initially hooked it up off the welder plug it was running through a dual pole 50 amp... I thought each leg of the dual pole was a 50 amp breaker feeding a 60 amp breaker on the unit... so when after 10 minutes of running the breaker popped... I assumed I'd drifted north of 100 amps. My friend gave me an old dual pole 70 amp to replace the 50... which is what is still incorrectly hooked up. And NO, I'm not about to continue running it like that. I like my space in non-charred form.

Frankly.... now that I know better (and should've known better before starting) I feel like a complete idiot.

--
I did alot of measuring and pondering out there this evening then doodled something up quickly. As you can see I'm thinking of moving the AHU to near the panel in a position that the 16" trunk can reach from within the trusses. The plenum will be 28"x21"x60", allowing for 2' tall intake box at the base. The trunk is 35'. I figured 8" ducts leading off the trunk 10' to the west and 2-3' to the east. I'd like to go further east, but that would require more duct and dipping down below the trusses due to the lower roofline. The duct at the NE corner will have a 4" tap going to the bathroom and the 8" at the SW corner will have a 4" tap leading to the doghouse. This is all approximate and not based on any calc's beyond what's been offered here (THANKS!).

Depending on affordability, I may start with all or part of the trunk with the take-offs mounted up so I can add the ductwork and registers later. I'm having the plenum fabbed tomorrow by the guy I talked to earlier. A buddy of mine from college actually mentioned this evening that his B-I-L is a HVAC guy and a mechanic in the town I live in (pop 2500)... small world. So I may hit him up about the ductwork past the plenum.

Please review, make comments, suggestions, re-size or re-route duct, etc. I'm open to all suggestions as I'm obviously a bit out of my element with this and the help I've gotten so far has been an immense benefit.

Doodle:
35'X40' (25'X40' in the main bay, 10'X40' in the east lean-to)

Electrical Panel at center-left (back d/s corner of the truck). The trunk will run through the trusses directly above center. I could possibly run the east ducts down to the header between the posts and mount registers there? And yeah I have no idea why they didn't enclose that one corner or insulate the wall... I will be enclosing it, so consider that corner interior space as well.

Kitchenette and bathroom (this area needs heat for obvious reasons).

 

[JimL]

21" wide fan coils, I usually use a 19 1/2" wide by 16-18 deep plenum. 1/2" hemmed out on the bottom. outlet is somewhere around 19 3/8x11 on them. Making it short, keeps the knockouts exposed in the top of the unit to run wiring. Don't forget you need reductions in your trunk line at certain points. Otherwise all your air is going to want to blow out the ones at the end of the line.

 

[Social_Joe]

21" wide fan coils, I usually use a 19 1/2" wide by 16-18 deep plenum. 1/2" hemmed out on the bottom. outlet is somewhere around 19 3/8x11 on them. Making it short, keeps the knockouts exposed in the top of the unit to run wiring. Don't forget you need reductions in your trunk line at certain points. Otherwise all your air is going to want to blow out the ones at the end of the line.

Correction: It should have read 21" (wide) X 18" (deep). The entire unit itself is 22" deep. The outlet measures 19 1/4" X 11". So 19 1/2" wide X 18 deep with a 1/2 inch flange around the bottom would work perfectly.

I know I'm going to need to reduce the trunk at certain points. Hopefully I'll be able to sort that out today between the sheet-metal fabricator that's doing my plenum and the one my friend is related to locally. Or given an online calculator I can use with what little data I have.

BTW: I thought the building was 30x40, not 35x40. That makes it 1600 ft2 (including carport)... My house is 1400ft2 and I have another uninsulated 24x24. A year ago I would've loved to have this problem

 

[DPelletier]

OK;

1) not sure about your layout; if you are going to use a fully distributed duct system in the attic then I would consider offsetting the main vertically and installing in the centre truss space so the branches are equal length. You can do it as you've indicated but you will need branch balance dampers or diffuser/register face dampers (OBD's or radial dampers) to equalize flow.

2) It is common to use an extended plenum system (same size main for the full length) in many exposed applications. Seeing as how your shop is one zone you would then use dampers to adjust the flow from individual outlets. Alternatively, you can use a graduated trunk system which will tend to equalize the flows naturally. Extended plenum systems are used for asthetics as well as simplicity but graduated trunk systems are preferrable for performance and that's what I'd use if you go with a fully distributed system in the attic like the one you've drawn.

3) you don't need a run to the washroom; it isn't a bad idea but an exhaust fan with a door undercut will also work fine.

4) an HVAC tech isn't a sheet metal worker....I call them when my condensing unit quits; they call me when they have a ductwork question.

If you want to stick with the layout you have, let me know and I'll do the sizing for you.

Dave

 

[Social_Joe]

^PM Sent. You are a gentleman and a scholar sir.

 

[Social_Joe]

I'm not sure my PM went through.... so here is the jist of it.

OK;

1) not sure about your layout; if you are going to use a fully distributed duct system in the attic then I would consider offsetting the main vertically and installing in the centre truss space so the branches are equal length. You can do it as you've indicated but you will need branch balance dampers or diffuser/register face dampers (OBD's or radial dampers) to equalize flow.

There is a vertical support I forgot to draw in the truss sections, so it can't be perfectly centered, but if it was moved next to center, the trunk would need to be offset from the plenum or the AHU will block my man door. Also bear in mind I might extend the east ducts into the lean-to later and that would put the trunk basically close to center as I have it drawn. Go with whichever would be the most efficient/economical (balancing it with dampers or moving the trunk).

2) It is common to use an extended plenum system (same size main for the full length) in many exposed applications. Seeing as how your shop is one zone you would then use dampers to adjust the flow from individual outlets. Alternatively, you can use a graduated trunk system which will tend to equalize the flows naturally. Extended plenum systems are used for asthetics as well as simplicity but graduated trunk systems are preferrable for performance and that's what I'd use if you go with a fully distributed system in the attic like the one you've drawn.

Graduated makes more sense to me from a economic and efficiency standpoint. Granted I have no clue how to calculate it.

3) you don't need a run to the washroom; it isn't a bad idea but an exhaust fan with a door undercut will also work fine.

Fair enough, saves work and duct.

4) an HVAC tech isn't a sheet metal worker....I call them when my condensing unit quits; they call me when they have a ductwork question.

Point well made.
If you want to stick with the layout you have, let me know and I'll do the sizing for you.

Please do, I will owe you one for sure. I just downloaded a ductulator app and am now more confused than ever. I may not do the whole system/design in one jump, but if I have it I can do it in stages and eventually have a complete system.

I ran everything above the ceiling as they're only 9' high and between a 16" duct, garage door fittings, and lighting.... it would be pretty intrusive and I have dreams of finishing out the ceiling someday.
Dave

THANKS ,

Joe

 

[Social_Joe]

For clarification, the BIL of my friend I mentioned does sheet-metal fab on the side as I understand. But I've never met the guy, so I'm not counting any chickens.

Once I complete this project I want to start stick-framing, insulating, and sheathing between the posts. I'll probably go one or two bays at a time to spread the cost out.

 

[Social_Joe]

There is enough room to run the trunk is either position within the trusses.

And we have plenum.

 

[DPelletier]

Sorry, I've been ******* in meetings.

I will do a simple sketch with the sizes shown. Sizing the ducts is relatively easy, the guesswork is determining which areas should get what CFM. One big zone is no problem but your "dog run" for eg. is a WAG.

Just label or tell me which of those small runs is which and I'll sketch something and scan and email it to you.

In the interest of full disclosure, I am not a PEng. and will not be taking the time to do a full heat loss/gain calc on your shop (I doubt you'd have all the info that would be required to take it to that level anyway) but knowing the total airflow, it is easy for me to do a simple duct layout and sizing that will work.

Cheers,
Dave

 

[Social_Joe]

No problems, you're doing me a favor.

In that drawing, I have the small 4" run going to the doggy enclosure on the bottom left corner (SW Corner). Hopefully enough warmth will transfer into the enclosure that I won't need to force air into it, but it won't hurt to have it. My number/distribution of register was based on pure guesswork from what I've seen in completed projects and also attempting to get the air focused near the walls/corners.

The second little run up in the top right (northeast) was to go into the bathroom, it can be eliminated. I'll just leave the bathroom open, and/or install a vent fan.

No, I don't have the R-Values, etc you'd need and that's beyond my need for this basic of a project.

Thanks again.

 

[JimL]

4) an HVAC tech isn't a sheet metal worker....I call them when my condensing unit quits; they call me when they have a ductwork question.

Dave

Hey now, some are!

 

[pseudorealityx]

Within reason... here's what you can expect out of a take off...

4" take off - up to ~30 cfm
6" - up to ~75 cfm
8" - up to ~200 cfm
10 - up to ~350 cfm

Those assume that you don't do anything too silly with the flex duct. Keep it as straight as possible, and support it fairly often so you reduce sagging. Flex is ~3x worse than straight duct, as far as friction goes.