Ceiling support box size

[ebrown1972]

Hello everyone. I recently bought a century 3500 wood stove. I am currently looking at what I will need to get as far as piping goes and I have a question about the ceiling support box. Does the support box need to go from protruding just under the ceiling through the attic to the roof? I am trying to figure out what size of ceiling support box I will need. Is that as simple as measuring from the room ceiling to the roof to determine the size of support box I will need? I assume the support box has to completely fill the void between the ceiling and the attic roof. I hope I am being clear on my questions.

Also, I see some chimney kits have a ceiling support box and an attic shield. What is the purpose of the attic shield when using a ceiling support box?

Thank you for your time. I am green at this and this will be my first stove install.

Eric

 

[EatenByLimestone]

The instructions for box size will come with your kit. With mine, I cut the drywall (to the correct size) where I wanted the hole to be, then used 2x4s to frame to that size. This allows you to add a couple screws to better support the drywall edges. Then it was easy enough to slide the pieces into the prepared hole and screw them in. The hardest part is then using the plumb bob to transfer the hole straight up to the pitched roof. After getting it all together and checking clearances I needed to increase the size of the hole in the roof deck as I’d screwed up the plumb line transfer by about an inch.

 

[stoveliker]

The ceiling box has to be properly situated with respect to the ceiling. The (class A) chimney pipe above it is all that goes thru the roofing.
With the proper flashing there that will be sufficient.

 

[stoveliker]

Oh, and the attic shield is to prevent attic insulation from falling into the ceiling box, or against the class A pipe.

 

[Eman85]

Do you have a flat ceiling ansd an attic space? Or do you have a cathedral ceiling? If flat the box sits on the ceiling rafters and drops into the room. The class A chimney pipe sits in the box and goes through the attic and through the roof and the attic area would be shielded. If cathedral the box install from the outside and rests on the roof rafters.

 

[begreen]

Hello everyone. I recently bought a century 3500 wood stove. I am currently looking at what I will need to get as far as piping goes and I have a question about the ceiling support box. Does the support box need to go from protruding just under the ceiling through the attic to the roof? I am trying to figure out what size of ceiling support box I will need. Is that as simple as measuring from the room ceiling to the roof to determine the size of support box I will need? I assume the support box has to completely fill the void between the ceiling and the attic roof. I hope I am being clear on my questions.

Also, I see some chimney kits have a ceiling support box and an attic shield. What is the purpose of the attic shield when using a ceiling support box?

Thank you for your time. I am green at this and this will be my first stove install.

Eric

It sounds like you may be referring to a cathedral ceiling support box which in some installs have been installed up through a knee wall to the roof. It looks like a long box, from 12"-36" tall. However, if the ceiling is flat and there is an attic above, then a conventional ceiling support is used, which is only about 4" deep. On top of this goes an attic insulation shield which prevents any insulation falling into the support box.

How tall will the attic section of the chimney be?

Square or cathedral ceiling support box


DuraTech ceiling support box

Selkirk ceiling support boxes

 

[begreen]

This is an attic insulation shield on chimney pipe.

 

[ebrown1972]

Thanks for all of the replies. I do have a flat ceiling with an attic. I see that I will not need the long box and that was what I was confused about. Looks like I need the round short ceiling support box with an attic insulation shield. I assume it's ok to build your own insulation shield as long as you follow the clearance for combustibles correct? Your replies have helped me understand how it all goes together. Thanks so much,
Eric

 

[ebrown1972]

Thanks for the picture. That is exactly what I need

 

[30WCF]

It will still be a square box. The round shield has a square flange on the bottom to match the box. Your kit may have square trim as Eaten By Limestone has shown or mine is round.

Either way the ceiling box will be square and need a square box framed up to support it in the ceiling joists. The support box was smaller than the span of my ceiling joists, so I had to box it in. Only one side of the box is attached to wood that was original construction. Three sides have additional framing to support the box in the location I needed.

 

[begreen]

It will still be a square box.

That depends on the manufacturer. DuraTech's round SB is round on the topside too.

 

[30WCF]

That depends on the manufacturer. DuraTech's round SB is round on the topside too.

View attachment 326075

Ahhh. I assumed they would all be square.

 

[begreen]

I assume it's ok to build your own insulation shield as long as you follow the clearance for combustibles correct?

I'm not sure if the company would agree, but a 24" section of 12" round stove pipe with a storm collar probably would work ok. Whatever is installed, be sure the attic side of the support box is totally clean before enclosing.

 

[30WCF]

Now you have me questioning myself. I’m not sure if I remember if mine was square or round. I remember framing it up. I also remember over the years replacing several bathroom vents, and it seems every time I do that, I have to frame a new size for the new fan. Maybe I’m just confusing myself. I could have sworn I had a square box under that shield.

 

[ebrown1972]

A few more questions for all of you. Where is the best place to buy the kits from? Also, I have seen several chimneys that say it is triple wall pipe. I assume either double wall or triple wall pipe is fine to use?

 

[30WCF]

While it may not be “the best place”, I got all mine at the local Lowe’s Home Improvement. I think I needed to have the telescoping section shipped to store, but they have a complete line.
There are plenty of fireplace specific online stores too that have different options and professional lines.

 

[ebrown1972]

Thanks. I see that my local Menards has most all of what I need in the store minus the telescoping pipe too. I didn't realize the big box stores sold Class A pipe.

 

[begreen]

A few more questions for all of you. Where is the best place to buy the kits from? Also, I have seen several chimneys that say it is triple wall pipe. I assume either double wall or triple wall pipe is fine to use?

Triple-wall DuraPlus chimney is a value brand. It requires a bigger hole through the roof and is not as good quality as the double-walled DuraTech chimney.

Be careful getting a kit and make sure it will work and doesn't have unnecessary parts. Menards has good Selkirk prices though I'm not fond of their roof flashing.

 

[EatenByLimestone]

I got mine from the local hardware store. His price beat the online guys.

 

[ebrown1972]

I made a trip to my local Menards yesterday and purchased everything I need minus the telescoping stove pipe which I had to order online. Hopefully I can get everything installed in the next few weeks. Thanks again everyone.

 

[Crab]

If you didn't do it already, before the return date expires pull each section out of the box to check for dents. I did so at Lowes and too large a % were dented. Back on the shelf they went. The packaging is not the best.

 

[ebrown1972]

Yes, I checked all of them and all are good. Thank you.