Duct help?

pelican · Jan 2, 2013

Hi all, I'm hoping to get a few pointers for creating a duct. So I had to go with plan "B" or maybe it was plan "C", since the heat from my wood insert wasn't getting upstairs from the lower level of my raised ranch where the insert is.

I went ahead and cut in a "vent" in the ceiling downstairs and through the hardwood floor upstairs. So far it came out exactly how I wanted but instead of nice warm air coming up through the vent it more like cooler air. I was able to position the vents between the floor/ceiling joists and now it pulling air cool air from the entire joist cavity.

So now I want to create a duct so that the cool air won't be pulled from between the floors. I bought a piece of sheet metal and was hoping to bend a "box" and somehow get it up there to create the duct and then just seal it with some duct tape in the seams. If I'd have to guess, I'd say it's about 10 or so inches I need to box out.

I'm thinking this is a common thing to do and was wondering if anyone can give me any pointers to help me out with?

Thanks!

MP

MnDave · Jan 2, 2013

Yes, the cool air between the floors will just fall through the opening without something to block it.

I have a duct between floors but I could not go straight up. I needed to go about 6-7 feet horizontal. Needless to say I needed a fan.

I would say that you are on the right track. Since you are not planning to use a fan (for now)... I would make this opening as large in both directions as you can.

Depending on the location of the vent in relation to your insert it may help to keep the door to the lower level open so that it acts as a cold air return.

Since you are probably going to use a standard register and return grill you could use a standard sized duct. If you cannot find a big one at a local hardware store. You could ask a local HVAC place or find the parts online.

MnDave

PLAYS WITH FIRE · Jan 2, 2013

Take the measurements of the duct you want to create, cut the metal to have tabs or a long seam, pop rivet it together. Slide it into the cavity,maybe with some insulation on all 4 sides and tack it in. If more complicated post pix.

pelican · Jan 2, 2013

I guess I only have to worry about the two long sides since I cut the grill/return long ways in the joist so there's only a few inches from each end to the joists. My plan is to cut a piece of sheet metal approx 10" high X 14" wide with some xtra tabs that will allow me to tack it in to "Block" each end of the joist cavity. It would be a lot easier if I just cut a larger section of my ceiling out (sheetrock) but I'm trying to fit it in the 4" x 11" hole I cut for the register.

MnDave · Jan 2, 2013

pelican said:
I guess I only have to worry about the two long sides since I cut the grill/return long ways in the joist so there's only a few inches from each end to the joists. My plan is to cut a piece of sheet metal approx 10" high X 14" wide with some xtra tabs that will allow me to tack it in to "Block" each end of the joist cavity. It would be a lot easier if I just cut a larger section of my ceiling out (sheetrock) but I'm trying to fit it in the 4" x 11" hole I cut for the register.

Sounds good. Let us know how this works out.

MnDave

PLAYS WITH FIRE · Jan 2, 2013

That's what I'd do....if it is a cold side like mine will be maybe put some insulation around it.

pelican · Jan 2, 2013

That's a great suggestion with the insulation since it's very close to one end of the house. I also plan of putting another duct in the opposite corner of the room, but only if I get some heat to come upstairs from this one.

I'm just hoping I get some hot air to come up or it will be a huge waste of money...

MnDave · Jan 2, 2013

pelican said:
That's a great suggestion with the insulation since it's very close to one end of the house. I also plan of putting another duct in the opposite corner of the room, but only if I get some heat to come upstairs from this one.

I'm just hoping I get some hot air to come up or it will be a huge waste of money...

I am on Plan C... Plan A and B cost around $150. Plan C wastes $75 and adds a new $300 but is guaranteed to work.

My first fan and duct size was too conservative. Fan went from 250 CFM axial to 480 CFM centrifugal (quieter) . Duct went from 6 uninsulated to 8 inch insulated. I also changed to very open grille's vs typical HVAC register/return.

MnDave

PLAYS WITH FIRE · Jan 3, 2013

I dont know how much room you have in the joists but I am going to use 6" flex duct with a 6" duct fan in a "Y" and try pushing the warm air up and if not happy pull the cold air down. So it will be 6" fan above the insert to a "Y" and then 2 vents. I seen kits for a ton of money and thought I can make this myself. I use my laser thermo and get temps close to 100 degrees on my ceiling in burner room. Setup is insert in masonry in basement. The insert part is going to change though. I bought an offset adapter to move my insert out 15" to 21" but will only move it out the minimum of 15". I will also insulate the fireplace firebox with roxul and line with sheet metal. Should work beautifully.! Then I will build my duct system as I will be pumping a ton more heat into the room.

MnDave · Jan 3, 2013

PLAYS WITH FIRE said:
I am going to use 6" flex duct with a 6" duct

Since you do not have a long run you might be happy with the flow and temps.

The room that I am trying to move warm air into is a large master bedroom and bathroom on exterior walls with a vaulted ceiling. The 6" duct fan moved a decent amout of air at the higher speeds but the noise was a problem.

I current have an 8 foot run of 6 inch aluminum flex pipe and it cools the air too much. The air temp in the 12x12 ceiling box directly above my stove is around 95F. By the time it gets to the register it is 78F.

I ordered all my Plan C parts last night.

Good luck and let us know how these projects turn out. This will help other people with similar projects.

MnDave

PLAYS WITH FIRE · Jan 3, 2013

Oh i will, the offset starts tomorrow. The flex duct I am using is insulated and the run is basically from the "Y" 6' on either side. I use a fan to push the cold air down stairs and it makes a killer convective loop up the stairs but I am hoping this will help also. If pulling the hot air up does not work I will reverse the fan to push cold air down. That will come some time in the future not worried about it now....getting the insert out onto hearth is a must!

pelican · Jan 3, 2013

Just picked up a roll of insulation, going to cut some off and stuff it in and hope for the best. Once I get it packed in nice I'll cut a piece of sheet metal try to secure it to create the duct.

pelican · Jan 4, 2013

Ok, now I'm not sure what to do... I've tried plan A, B, and C and nothing has helped me get the heat upstairs to my main living area...I just purchased a Regency i2400 wood insert amd It seems to work pretty well and gets the 14 X 22 bottom floor's temp up to around 80 degrees but my temps upstairs remain at 62 degrees (average temp outside is mid thirties) no matter what I've tried. In my Raised Ranch style house you walk in the front door and take 7 steps up to get the upper level and 7 steps down, turn right and walk about 9 or so feet through a hallway to get to the room where the insert is.

Plan "A" was to just run the stove as is with the blowers and see what happens before I tried more extreme measures. Didn't work...

Plan "B" - I installed a 4" air circulating fan to help assist the warmer air down the hallway to get upstairs. I put the fan in the top corner of the room's doorway directing the air down the hallway. Didn't work...

Plan "C" - I cut a standard sized (12" x 4") vent in my downstairs ceiling/upstairs hardwood floor. I figured the hot air would "rush" up through the vent since the room downstairs gets pretty warm. It was more like cool air I feel slightly coming up. I also went ahead and insulated the ends of the joist where I cut the vent and that didn't help...

My Plan "D" involves cutting a second vent in the opposite side of the room to help draw the air up. I'm thinking I need two "holes" in order for the heat to displace. Before I do this I was hoping some of you could chime in to let me know what I'm not doing right or missing.

On the plus side, my furnace usually doesn't kick on while I'm burning so I am saving oil, I just wish I could spread the heat through my house a little better. Anyone have any ideas why I can't get the heat upstairs and any suggestions? I just had all new windows installed in the house, do you think that has anything to do with it? Could my upstairs be too airtight?

Thanks,
MP

nellraq · Jan 4, 2013

pelican said:
Ok, now I'm not sure what to do... I've tried plan A, B, and C and nothing has helped me get the heat upstairs to my main living area...I just purchased a Regency i2400 wood insert amd It seems to work pretty well and gets the 14 X 22 bottom floor's temp up to around 80 degrees but my temps upstairs remain at 62 degrees (average temp outside is mid thirties) no matter what I've tried. In my Raised Ranch style house you walk in the front door and take 7 steps up to get the upper level and 7 steps down, turn right and walk about 9 or so feet through a hallway to get to the room where the insert is.

Plan "A" was to just run the stove as is with the blowers and see what happens before I tried more extreme measures. Didn't work...

Plan "B" - I installed a 4" air circulating fan to help assist the warmer air down the hallway to get upstairs. I put the fan in the top corner of the room's doorway directing the air down the hallway. Didn't work...

Plan "C" - I cut a standard sized (12" x 4") vent in my downstairs ceiling/upstairs hardwood floor. I figured the hot air would "rush" up through the vent since the room downstairs gets pretty warm. It was more like cool air I feel slightly coming up. I also went ahead and insulated the ends of the joist where I cut the vent and that didn't help...

My Plan "D" involves cutting a second vent in the opposite side of the room to help draw the air up. I'm thinking I need two "holes" in order for the heat to displace. Before I do this I was hoping some of you could chime in to let me know what I'm not doing right or missing.

On the plus side, my furnace usually doesn't kick on while I'm burning so I am saving oil, I just wish I could spread the heat through my house a little better. Anyone have any ideas why I can't get the heat upstairs and any suggestions? I just had all new windows installed in the house, do you think that has anything to do with it? Could my upstairs be too airtight?

Thanks,
MP

nellraq · Jan 5, 2013

Whoops -- messed that reply up!!

Try cracking open a window in the room that you are trying to heat.

If your room is too airtight, the hot air from the basement will not move very much. It has to displace something (ie. an equal amount of air in the room you are trying to heat.)

I had a similiar situation in my house with my forced air heating. I have a small suite on the end of the house. The installers put hot air ducts into the suite, but virtually no air/heat entered. They didn't install a cold air return. I opened a window a little, and the 400 square foot suite heated up quite quickly. Now it's got a cold air return and it works well.

Maybe this is a long shot, but it's certainly worth a try!

weatherguy · Jan 5, 2013

Your probably going to need another vent to get a good loop going. I have my insert in the family room on the ,lower level and I thought the heat would rise up into the upper level through the open stairway, instead the cold air comes down and not as much hot air as I wanted would go upstairs, most of it was trapped in the lower level which was always 80. I cut a a vent, forget the size but looks about 6" x 20" on the opposite side of the room from the stairway, now I got a loop going and much more hot air comes upstairs, doing that and a block of plate and the whole house is comfortable now.

MnDave · Jan 5, 2013

Relying on warm air bouancy to create air movement can be tricky. It works in a chimney due to the higher temperature differences which create large differrences in air density and hence bouant air forces. But the small temperature difference between the two floors is small. And when they are become the same the movement due to bouancy ceases comepletely .

The stack effect due to warm air rising and leaving through leaks on the upper level creates a negative pressure in the lower level relative to the upper level. The main movement of air due to the stack effect is through the stairwell connecting the levels.

That small opening you are making is very small compared to the opening of the stairwell so very little air will move through the small opening as a result.

You can test this by closing or throttlling the opening to the stairwell if possible. Unfortunately this may prevent air distribution that you are currently happy with.

The advise that nellraq gave ... "opening the window in the room you are trying to heat" is a good demonstration of stack effect. Especially if you you can close off the room from the rest of the house. You should be able to pull air through your small opening but having an open window won't work for obvious reasons.

In my opinion, another opening will have the same effect as the first. It will not work as a return to the other being a supply due to the stack effect in the house. I doubt that you will be able to block enough leaks to make this work.

This is where a properly sized fan becomes neccessary. It ceates a pressure differential greater than the stack effect and allows air to flow in your smaller opening.

MnDave

weatherguy · Jan 5, 2013

MnDave said:
Relying on warm air bouancy to create air movement can be tricky. It works in a chimney due to the higher temperature differences which create large differrences in air density and hence bouant air forces. But the small temperature difference between the two floors is small. And when they are become the same the movement due to bouancy ceases comepletely .

The stack effect due to warm air rising and leaving through leaks on the upper level creates a negative pressure in the lower level relative to the upper level. The main movement of air due to the stack effect is through the stairwell connecting the levels.

That small opening you are making is very small compared to the opening of the stairwell so very little air will move through the small opening as a result.

You can test this by closing or throttlling the opening to the stairwell if possible. Unfortunately this may prevent air distribution that you are currently happy with.

The advise that nellraq gave ... "opening the window in the room you are trying to heat" is a good demonstration of stack effect. Especially if you you can close off the room from the rest of the house. You should be able to pull air through your small opening but having an open window won't work for obvious reasons.

In my opinion, another opening will have the same effect as the first. It will not work as a return to the other being a supply due to the stack effect in the house. I doubt that you will be able to block enough leaks to make this work.

This is where a properly sized fan becomes neccessary. It ceates a pressure differential greater than the stack effect and allows air to flow in your smaller opening.

MnDave

Dave can you give me some info on these fans you've mentioned? thanks

PLAYS WITH FIRE · Jan 5, 2013

Maybe to duct with two fans pulling the cold air down fill also force the warm air up through the hall way. Try using a box fan laid atop the duct pushing the cold air down into the stove room.

pelican · Jan 5, 2013

Didn't get a chance to cut a vent in today. My wife bought me a home beer brewing kit for Xmas and I went to a class on how to brew, very cool... I got to drink something while enjoying my fire, right?

Anyway, tomorrow I'm going to cut another vent in the opposite side of the room. A few suggested to crack a window and I've actually tried that but not after I cut the vent so I'm going to let my family room get nice and warm tonight and crack the window if the room I'm trying to heat and see if that helps.

I'm thinking a second vent in the opposite side of the room would act like if you had a can of juice and popped one hold in the juice wouldn't come out well but when you popped a second hole in the opposite side it comes out freely. I'm kind of hoping that's what will happen with my second vent...

With the temperature difference of 15 degrees, I would imagine this heat has to be able to get upstairs some way or another...

MP

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