extending HVAC ductwork. Hard to DIY?

[Aharami]

My main furnace/blower is up in the attic and has a hard time warming up the 1st floor adequately during the winters. Well my basement has a separate furnace/AC for the basement alone. I recently replaced this furnace with a new high efficiency one since the old one was dying. I'd like to cut out some floor registers on the 1st floor and extend the basement ductwork to share some of the heating between basement and 1st floor. That way, 1st floor will be heated mainly by main furnace up in attic, but also by basement furnace when it kicks on.

First of all, this is the layout of my basement. As you can see, current duct runs along right wall

I'd like to take part of the duct down, and cut two holes on top to create feeds for the new 1st floor registers.

(1) register will sit right on top of where duct lies. So that new duct will just go straight up between the ceiling joists and thru the ceiling/floor.

(2) register will sit on the other side. So for this one, I'd like to up from the current duct into the ceiling cavity, make a 90° turn and go across between the ceiling joists so that I can have a flat ceiling when I finish off the basement.

This is my plan anyways. But since I've never done this before, I'd like to know if there's something I'm not thinking of, or not aware of. How big of a duct will I need for the cross run? Will a 7" round suffice? The cross run will be about 13-14'. What should I know when performing this. Any info helps. Thanks

 

[Sea Moose]

hvac contractor
<---

Get a hvac contractor

You dont have the right gear and the sheet metal guy will. Trust me on this.

 

[Rubycon]

hvac contractor
<---

Get a hvac contractor

You dont have the right gear and the sheet metal guy will. Trust me on this.

It's not hard to cut a hole in those ducts and put panning between those joists. If he makes it tight there will be minimal loss to the other side. The long run alternatively could use flex.

A "sheet metal guy" just has better tools and fancy things like a jersey lock maker and machine to make slips and drives for locking pieces together, a brake, etc. A DIY does not really need to get into that unless they need to move their air handler and in need of collars and transitions, offsets and such.

 

[BarkingGhostar]

You want to over work the basement unit because you feel the attic unit cannot handle the heating/cooling load? Just because the new unit is high-efficiency doesn't mean it can perform continuously above its design load.

Considering the location you are at why not consider a pellet stove for the first floor? I would imagine that would be better than overworking the basement unit.

 

[Sea Moose]

It's not hard to cut a hole in those ducts and put panning between those joists. If he makes it tight there will be minimal loss to the other side. The long run alternatively could use flex.

A "sheet metal guy" just has better tools and fancy things like a jersey lock maker and machine to make slips and drives for locking pieces together, a brake, etc. A DIY does not really need to get into that unless they need to move their air handler and in need of collars and transitions, offsets and such.

I hate it when you undermine me.

 

[krylon]

I think you're fucked, brah.

 

[Aharami]

hvac contractor
<---

Get a hvac contractor

You dont have the right gear and the sheet metal guy will. Trust me on this.

not an option. I'm not paying more for this. If I can't do this myself, I'm not doing it. yea I'm sure I dont have the right gear. but the only place I can see myself having to fabricate something are the ducts going up straight to register 1 and the one before the right turn for register 2

 

[Vette73]

Yea its not that bad. Get some round boots and cut a hole in the metal. Attach the boots with sheet metal screws and use some mastic to seal up. Then attach some Flex duct work and run it to your vent.

I would use 6" as its easy to come by and should provide enough air.
Also don't run to many at first as it will reduce the air in the basement and the air entering the first floor will not adjust the temp for the thermostat in the basement. i.e. the air can run all the time and never turn off it not set correctly.


<-- Did all the AC/Heat work in house (with help from dad )

 

[Greenman]

Off topic, but why is the insulation in your floor system upside down? Around here the vapor barrier is always on the conditioned side .

For your heat everything you need is at the homedepot. Use flex with giant zip ties and foil tape. Don't use duct tape, sealing duct's is the one place it always fails.

If the system you just replaced isn't doing the job, contact the installer and have him come correct his work.

 

[Flipped Gazelle]

My main furnace/blower is up in the attic and has a hard time warming up the 1st floor adequately during the winters. Well my basement has a separate furnace/AC for the basement alone. I recently replaced this furnace with a new high efficiency one since the old one was dying. I'd like to cut out some floor registers on the 1st floor and extend the basement ductwork to share some of the heating between basement and 1st floor. That way, 1st floor will be heated mainly by main furnace up in attic, but also by basement furnace when it kicks on.

So, you don't want to control the the output of the basement furnace - that is, the furnace comes on at a certain temp on the 1st floor, then goes off at a certain temp - you just want to the extra heat when it does come on, like a "bonus"?

<-- used to be a tin knocker

 

[Aharami]

You want to over work the basement unit because you feel the attic unit cannot handle the heating/cooling load? Just because the new unit is high-efficiency doesn't mean it can perform continuously above its design load.

Considering the location you are at why not consider a pellet stove for the first floor? I would imagine that would be better than overworking the basement unit.

will adding two more openings really over work it though? It's a 45k BHUh Ruud 2 stage furnace that has 890 CFM at low setting, and 1140 CFM at high. Right now the basement duct has 3 registers, and the basement is 500 sq ft. after finished off, the heated area will be ~400 sq ft.

The return air will remain where it is. I will create a partition wall where the return box begins, and the furnace will be getting it's return air from the finished part of the basement.

 

[Aharami]

Off topic, but why is the insulation in your floor system upside down? Around here the vapor barrier is always on the conditioned side .

For your heat everything you need is at the homedepot. Use flex with giant zip ties and foil tape. Don't use duct tape, sealing duct's is the one place it always fails.

If the system you just replaced isn't doing the job, contact the installer and have him come correct his work.

yea i installed that wrong. but no matter, once the basement is finished off, it will only act as a soundproof barrier

the new one in the basement is working fine. Its the one in the 3rd floor attic, the main one, that has a hard time pushing the hot air down to the 1st floor.

 

[Aharami]

So, you don't want to control the the output of the basement furnace - that is, the furnace comes on at a certain temp on the 1st floor, then goes off at a certain temp - you just want to the extra heat when it does come on, like a "bonus"?

<-- used to be a tin knocker

yep, exactly right. thermostat and return for basement furnace will remain in basement. thermostat for main furnace is on 1st floor (I wont be putting the new registers anywhere near the main thermostat). The basement furnace will kick on when it wants to, and throw some added air into the first floor as a bonus

 

[runzwithsizorz]

You&#8217;re my kinda guy, Aharami! This is an easy DIY project, and you&#8217;re not stupid, you just lack the knowledge of what parts, and materials exist. Once you see them, I&#8217;m sure you will know what to do. 6&#8221; is probably adequate, and with the insulation between your joists, your not gonna get much larger, (but maybe 8&#8221. To avoid buying special tools to work in a cramped space, just bring that section of the main trunk down, MARK IT FIRST. You do know how to do that don&#8217;t you? Hint, pull the cleats, and try not to bend them, they are a bitch to slide back on if you do, and when you do, tape them, ALL OF THEM! You will need,----
1 saddle tap
1 90-degree register boot
1 straight register boot
1 dovetail collar
2 registers (upstairs)
Insulated flex duct
Foil duct tape
A few short self-tapping screws
Wide hanging straps
A 12 pack of beer
Hold the boots up to the floor, and trace around the inside with a pencil. Drill holes in all four corners, and shove something up through those holes so you can find them topside. It&#8217;s always easier to cut out your hole from above, especially if it&#8217;s carpeted. And speaking of carpet, do not dilly-dally, or not use reverse, or you may wind up with half your carpet wound around your drill bit, (been there, done that).
Visual aids; https://heatac.com/index.php?cPath=22_48&osCsid=e3jdidcu00in9mcbmaj42gfrf2

http://www.theductshop.com/shop/catalog-saddle-taps-flat-c-1_9.html

 

[Aharami]

thank you!! exactly what I needed to know

 

[Aharami]

the space between the ceiling joists is 10" wide. not sure if a 4x10 register will fit in there. It wont look right turned 90&#176; as it will be going by a wall and it would look like it is sticking out perpendicular from the wall. I was hoping they make 4x8 registers, but I dont see anything shorter than 10" long here. Maybe HD or Lowes has something.

Also what is the dovetail collar/crimped collar used for? For the long run, I'll be going main trunk line > saddle tap > flex duct > 90 register boot, right? Where does the dovetail collar fall?

 

[runzwithsizorz]

the space between the ceiling joists is 10" wide. not sure if a 4x10 register will fit in there. It wont look right turned 90° as it will be going by a wall and it would look like it is sticking out perpendicular from the wall. I was hoping they make 4x8 registers, but I dont see anything shorter than 10" long here. Maybe HD or Lowes has something.

Also what is the dovetail collar/crimped collar used for? For the long run, I'll be going main trunk line > saddle tap > flex duct > 90 register boot, right? Where does the dovetail collar fall?

10" joist space huh? No problem, secure it by drilling through the back sides of the joists, a 90 degree drill attachment would be handy. but don't drive the screw up too high, for you may stop the register from sliding down all the way. The crimped collar is what you will will use with a VERY short piece of flex duct for the straight up register boot. Also I should have said, BASEMENT register boots, they have a flange.
More visual aids;
http://www.standexadp.com/catstyle.php?prodcode=FG25&groupname=Register Boots

 

[iGas]

Sorry the thread craping but, I have something to get off my chest here.

As a contribution member I feels that the mods here are out of touch with reality, because they favored useless member/s and promotes self centered people to mod position/s instead looking at AT as a collective that strives to serve and better society.

That said.

Basement sq is 500, suggests 1 ton with 400 CFM blower (similar for furnace) is more than enough to serve it. Over sizing the heatpump isn't bad but it is not going to be as energy efficient as correct sizing, and over sizing will not remove as much water (humidity) from the air as correct sizing.

Two 6" round ducts with 12"x4" registers should be sufficient for the basement, however you might want to add at least a total of 24"x24" return register/s with similar size duct work for return air (to both main floor & basement if the basement heatpump is going to serve them floors). Best result is a total 24"x36" return register/s as your heatpump is close to 1200 CFM (suggest that it is close to 3 ton) with duckwork similar in size. However, you may use smaller return air ductwork as compare to register size if you don't mind higher friction noise, but I wouldn't go much lower than 12"x24" duct as return (undersize return creates high friction, that force the blower to step down in speed/CFM hence it will never be able to run in high mode for heating/cooling).

The basement heatpump should be able to serve 1200~3000 sq of living space pending the insulation quality/efficiency of the house. It should be able to serve both the basement and the main floor. 3 ton heatpump should be able to handle a total max of 600" of supply air register surface or a total of 12.5 (13) 12"x4" registers (or 17 12"x3" registers) pending length duct runs & bends.

Also have a HVAC mechanic service the heatpump in the attic to make sure that it is running correctly (low refrigerant and or leaks, failed compressor, etc....), and check the blower to make sure that it is running correctly, as well as replacing the filter every 3~4 months, and make sure that the motor is running well so as the belt (replace belt if it show sign/s of wear). And, make sure that the heatpump is off before you service it.

Good luck!

 

[MikeyIs4Dcats]

It's not hard to cut a hole in those ducts and put panning between those joists. If he makes it tight there will be minimal loss to the other side. The long run alternatively could use flex.

A "sheet metal guy" just has better tools and fancy things like a jersey lock maker and machine to make slips and drives for locking pieces together, a brake, etc. A DIY does not really need to get into that unless they need to move their air handler and in need of collars and transitions, offsets and such.

flex should not be used for runs more than 6'.

And he's not simply "panning" the bottom of the joist....they only do that for returns, not supply.

the skill here is in determining if the unit will have enough capacity to do what he wants, otherwise he may end up with a cold main floor and a cold basement if he messes up the distribution. Also, in determining if there will be too much static pressure to overcome the added ductwork for the new drops.

this would likely only run you a few hundred bucks from a small HVAC contractor and would be worth the extra money, from a guy who's big on DIY.

 

[iGas]

flex should not be used for runs more than 6'.

And he's not simply "panning" the bottom of the joist....they only do that for returns, not supply.

the skill here is in determining if the unit will have enough capacity to do what he wants, otherwise he may end up with a cold main floor and a cold basement if he messes up the distribution. Also, in determining if there will be too much static pressure to overcome the added ductwork for the new drops.

this would likely only run you a few hundred bucks from a small HVAC contractor and would be worth the extra money, from a guy who's big on DIY.

Pending design, manufactured flex run can be as long as 30'.

 

[MikeyIs4Dcats]

Pending design, manufactured flex run can be as long as 30'.

I supposed IRC may allow it, but as far as commercial here we are limited to 6'.

 

[Rubycon]

Sorry the thread craping but, I have something to get off my chest here.

As a contribution member I feels that the mods here are out of touch with reality, because they favored useless member/s and promotes self centered people to mod position/s instead looking at AT as a collective that strives to serve and better society.

Oh don't worry.
There will be no more useless contributions from me.
Just let me get this off my chest though.
I don't tout ANY expertise and should not have to. I've been around much more collective expertise and picked up things here and there. If people want to think I'm nothing more than a useless idiot googling and reading from textbooks [sic] then fine. I'm not familiar with codes but understand fundamentals of this stuff works.

Back to reality here and no more posts from me - ever.

You can eat your cake now. I'm done now.

 

[lxskllr]

Wtf?!

 

[iGas]

Oh don't worry.
There will be no more useless contributions from me.
Just let me get this off my chest though.
I don't tout ANY expertise and should not have to. I've been around much more collective expertise and picked up things here and there. If people want to think I'm nothing more than a useless idiot googling and reading from textbooks [sic] then fine. I'm not familiar with codes but understand fundamentals of this stuff works.

Back to reality here and no more posts from me - ever.

You can eat your cake now. I'm done now.

There are times that your post/s doesn't make sense to me, but IMHO the majority of you post/s are concise and well deserved as good posts in my book.

PS. The rant isn't toward you Rubycon.

 

[Sea Moose]

Oh don't worry.
There will be no more useless contributions from me.
Just let me get this off my chest though.
I don't tout ANY expertise and should not have to. I've been around much more collective expertise and picked up things here and there. If people want to think I'm nothing more than a useless idiot googling and reading from textbooks [sic] then fine. I'm not familiar with codes but understand fundamentals of this stuff works.

Back to reality here and no more posts from me - ever.

You can eat your cake now. I'm done now.

Nooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooo