fan in a stove alcove wall?

[robman]

Hi
I live in earthquake country and as a result, removed our masonry chimney. The chimney had cracks when we moved in so we had installed a Lopi Patriot and a stainless steel liner through the chimney. We will now have an alcove where the fireplace was and will reuse the Patriot with double wall metalbestos chimney running through the attic and out the roof. I have two questions--first, I like the look of Rumford fireplaces as well as their mechanical advantage of having more heat move forward.

Does angling the walls of the alcove give any similar advantage? (My idea is to first put up two layers of wonder board around the alcove to more or less fireproof it and then frame inside of that with steel framing which will have more wonder board and tiles.) There is not enough clearance behind the stove so we will probably do the 1" air gap up that wall.

The second question deals with blowing the hot air from the stove into the room. Our house was built in 1910 and has little insulation and single pane windows but we are in a moderate climate SF Bay Area). It would be nice to get more air flow for the heat produced. We had an ecofan but that did not seem to get much air movement. I am thinking of putting an electric fan towards the top of the wall above the wood stove. It would blow from the alcove into the dining room. is this done and does it make sense? Do I need special fan and metal shroud if it is up 8'? Any recommendations?

I am thinking I will probably go up one 4' section of single wall pipe before switching to double wall. Does that make sense? All of this is being done with a building permit.

Thanks

Rob

 

[begreen]

Welcome. I am not sure there will be any advantage to sloping the rear wall. The stove will radiate little heat from the rear. First and most importantly, meet or exceed the manual's alcove clearance requirements. If you do then there is no need for the wall shield with the air gap. If you want to reduce the gap to the non-combustible spec with tiled cement board, that would be fine too.

For the fan, try this trick. It's easier to blow cold dense air into the heated space. Try placing a common 10-12" table fan or box fan on the dining room floor facing the stove room. Run it on low speed. The cooler displaced air from the dining room will be replaced with lighter warm air from the stove room.

 

[xman23]

Second, BG's air trick. That is to get heat into a back room, you need to get the cold air out along the floor. Then the hot air will replace it. Fans do move heat off the surface of the stove. But they do make noise. I don't need or use one. And never saw any difference with one on the stove.

Just meet all the required clearances and hearth. Me and many here use single wall pipe out of the stove, until it goes into the ceiling box that transitions to double wall. On my single wall i have a rear heat shield because of the cathedral ceiling. I get a lot of heat off the single wall. And it hasn't made the rest of the chimney to cold.

 

[robman]

Thanks Tom and BeGreen
So, will the fan on the floor remove some of the hot air from the top of the alcove? In other words, I'll have a 9' ceiling but the front of the alcove will only be about 5' high to the mantel. Also, I have plenty of clearances on the sides but not on the back, which is why I was thinking of covering the shear wall (my engineer spec'd it) with cement backer board or type x sheetrock (2 layers) and then doing the offset circulating behind the tiled back wall. Is that not necessary if I just put up 2 layers of cement backer board? Are the fans that go under the wood stoves as effective as a small box fan right outside the stove?

Thanks again for your help

Rob

 

[begreen]

So, will the fan on the floor remove some of the hot air from the top of the alcove? In other words, I'll have a 9' ceiling but the front of the alcove will only be about 5' high to the mantel.

Might be best to do a sketch here. If the alcove ceiling height is lower that 84" it must be properly shielded. I would also slope the alcove ceiling to encourage nature convection out of the alcove. The sheer wall detail is overkill. You can use regular sheetrock as long as it is behind a proper NFPA 211 wall shield that is vented top and bottom. The shield with its ventilated air space is what is protecting the combustibles behind it. If you want to overkill, just use cement board instead of sheetrock for the ceiling behind the heat shield that would be fine.

Do you mean the factory fan? The Patriot is a bargain stove so it factory blower just blows up the rear of the stove to a deflector at the top. If you take a look at the Lopi Endeavor or Avalon Rainier you will note that these stoves have a convection deck that directs the air over the top of the stove. These are more effective. You might be able to fab up a convection deck for this purpose. Highbeam posted a homemade version for his 30NC.
https://www.hearth.com/talk/threads/blower-for-nc30-upgrade-options.139673/

 

[robman]

Hi BGreen
The shear wall is for seismic purposes. We removed a brick chimney and added a basement to our house when we needed to redo the foundation (built in 1910 most likely with bay sand and then we believe a 6' prohibition basement for 1/2 the house. The retaining walls had no footings). All this is based on seismic upgrades. I will take a photo later to explain if you feel it is still helpful. We have what looks like a closet which is where the chimney used to be. I had bought the Patriot and a flexible stainless flue liner to allow us to have fires. There were otherwise too many cracks in the chimney etc. We removed all that but kept the patriot. We had bought the Patriot because it was one of the few stoves that fit into our firebox. While everything is open I would consider buying a different stove that has tighter clearances or better venting characteristics with a fan. The alcove is in an interior wall, between the dining room and kitchen. My idea for the alcove is to have it look somewhat like a fireplace with a wood stove placed inside. It will have an opening and a mantel above it.

I think I was describing my interpretation of NFPA211--to have cement board or type x sheetrock over the pre-existing shear wall and then have vertical 1x1 aluminum or steel rod running vertically on that wall with a 1" gap at the top and bottom and then tile. Is that not correct and doesn't that allow me to halve the required distance?

On another note, I think you are suggesting a lowered ceiling for the alcove instead of keeping it at 9'. Are you suggesting using steel studs to build a lower heat shielding ceiling in the alcove?

Thanks again

Rob

 

[robman]

Hi

the alcove measures 61" wide (to wood framing), 60" from plywood subfloor to where the mantel will go (to wood framing) and is 33" deep. The height to the ceiling framing is 112". I am attaching a few photos.

Thanks again
Rob

 

[begreen]

Your house construction and lack of foundation was similar to ours. I did the same thing and raised the house 3ft onto its new foundation. But instead of an alcove I relocated the stove as a freestander.

It's the mantel description that concerns me. It sound like the alcove will have a high ceiling, but will have a face dropping down to the 5' level. The picture seems to reinforce this. Is that correct? If so, the interior of that large cavity above the stove is going to get quite hot as it collects most of the heat rising off the stove. My concern would be pyrolysis if there is any wood behind this construction. A large grille at the top of the alcove would greatly help vent some of this heat accumulation. Moving the stove out a bit into the room could also help, especially if you added a convection deck on the back half of the stovetop, as mentioned earlier.

Or another thought would be to start the alcove ceiling at the mantel level with proper ceiling heat shielding as mentioned in the manual. Or skip the mantel and open up the wall cavity. If you do put a mantel in, will it be non-combustible? If it is combustible, then heat shielding will need to continue for the mantel to an inche past its forward edge.

 

[robman]

Thanks Begreen. You are right about the heat in the alcove, which is why I was asking about a fan towards the top--in order to blow out the hot air from the alcove. If I just use a vent, are there any made for this specification or any fans anyone knows of? I was planning on using a 4x6 recycled old growth fir for the mantel. I should look again at the Lopi owner's manual to see how much above the stove it needs to be in order to not have a heat shield protruding an inch. I think with type x sheetrock over the existing wood and then framing the sides with steel framing and then cement backer board and tiles, we'll be OK on the sides. I was thinking that on the back, we'd do type x rock (not sure if we need one or two layers) and then 1" tubular aluminum or steel with the 1" gap at the bottom and top and tile that.

On a second note, I have a 8 in 12 comp shingle roof that I plan on replacing in the next year or two with standing seam. Is there a jack that would work with bot and if not is there an economical way of bringing the metalbestos through the roof?

Thanks again

Rob

 

[begreen]

That large heat trap has me concerned. I would try to design it out if possible. A fan is not acceptable as a heat relieving device. What if there is a power outage? I'd want a grille there so that heat can convect out naturally. That is a wide area so it may take two grilles, say 8" x 30. These can be simple return air grilles or something fancy or custom made out of expanded metal covering a framed opening with a nice trim frame.

The clearances from combustibles to the top of the stove with heat shielding are pretty low for this stove. That's why I suggested having the alcove lid at the mantel height and a little lower in back. The alcove ceiling heat shield can be just sheet metal on 1" standoffs. That metal can be painted black and continue under the mantel.

 

[begreen]

For the alcove ceiling if it's carried all the way up I'd want a grille on the top face so that heat can convect out naturally. That is a wide area so it may take two grilles, say 8" x 30. These can be simple return air grilles or something fancy or custom made out of expanded metal covering a framed opening with a nice trim frame.

The chimney goes through the roof the same way whether composition or metal roof, Just change out the flashing when you do the metal roof for a special one that is designed for metal. Excel makes a good flashing for metal roofs.
(broken link removed)

 

[robman]

Thanks again Begreen. So if it were your house would you put a heat shield at the mantel height or go to the ceiling and have two grilles? I am a woodworker so making the grills doesn't worry me. If I were to do the shield at mantel height, I'll probably use backer board and large (12x24) dark gray or black tiles so it is not too obvious.

Thanks again

Rob

 

[begreen]

If it were my house, the large empty dead cavity above the mantel would bother me. I'm not sure if I would cap the alcove at the mantel level and use the dead space for another purpose like shelving, a cabinet or something else or let it be and vent the heat at the top of the cavity. Worth thinking about the options, especially as a woodworker. Is the back side of the alcove space exterior wall?

 

[robman]

Hi Begreen
Thanks for the quick response. The back of the alcove has the shear wall and the other side is the kitchen--the hood is there and with the shear, we cannot put a cabinet from the other side. Are you saying that I should cap the alcove at the level of the mantel and add a grill above? , and if so what would allow the air to circulate (where would it draw from)? And is it OK to do the cap in backer board and tile?

Thanks again

Rob

 

[begreen]

No, I have made a couple suggestions. One, to cap the alcove at the mantel height. You can't do this with many stoves, they require at least an 84" ceiling for an alcove, but with proper ceiling heat shielding it is allowed with the Patriot. The other option is to proceed with the large cavity and high alcove ceiling, but ventilate the cavity at the top with a grille. Or just open up the space and don't have a mantel.

 

[robman]

Thanks again Begreen
It sounds like if I were to ever consider changing the stove, I'd be better off with a grill at towards the top of the alcove. Do you know of any nice examples that I could use as a guide for a craftsman style home?

Thanks again

Rob

 

[begreen]

It sounds like if I were to ever consider changing the stove, I'd be better off with a grill at towards the top of the alcove.

(broken link removed to https://www.pinterest.com/explore/vent-covers/?lp=true)
Note, there are not many stoves that have the Lopi low alcove clearances. Keep that in mind if a change is planned.

 

[robman]

HI BeGreen
Thanks again. I decided to go to the top of the alcove with type x sheetrock and then cement board wight eh required gap etc. and we will put a grille at the top of the alcove (building it so that I can upgrade the stove at some point). Is there a formula for size of the grille? I like the Reggio Grilles and can put in one as large as 14x26. Is that overkill? I think it will be 2" below the ceiling of the alcove. I could also have two smellier ones side by side.

Thanks again

Rob

 

[begreen]

LOL, auto-correct really mangled that post. Rather than smellier grilles I think a pair or 8" x 20 might look better, though if you custom make then it really only needs to be a slot that completely vents the top air gap. Something like 2" x 48" would also work.

 

[robman]

Not "two smellier ones" but two smaller ones....

 

[robman]

Thanks. I will probably go with something pre made and like the reggio grilles. Will having 2" above the top of the grill to the top of the alcove be a problem? If it is, I can probably fur down the ceiling of the alcove. I am assuming that if you think a 2"x48" grille will work that 96 square inches (little more than .5 sq foot) is enough air movement. Thanks again

Rob

 

[robman]

Hi again
As we are getting closer and framing the alcove, I have a question about the chimney pipe within the alcove. I am thinking I'll put a 24 wide x 12" tall Reggio register as close to the ceiling of the alcove as I can and it will be centered. Will that work or must the register go the entire width of the alcove? Also, I assume that it would heat more if I use single wall pipe for most of the alcove before going in to the attic and then out the roof. How do I transition from single wall to double and support the weight of the double wall (metalbestos)? Lastly, must I buy a metalbestos through the floor kit going to the attic or can I frame a box with backer board with the required clearance and have that go through the attic floor? Thanks again for all of your help

Rob

 

[begreen]

The register should allow unrestricted airflow from the ceiling heat shield. A pair of 24" x 6" would work better for this.

The chimney pipe is supported by a ceiling support box with an attic insulation shield on the attic side. I would use double-wall stove pipe to connect the stove to the chimney. Have you checked out Metalbestos's documentation on installation of chimney and stove pipe?
http://www.selkirkcorp.com/sitecore/content/global-configuration/selkirk/products/chimney/ultra-temp
This video may also be helpful.
(broken link removed to https://www.rockfordchimneysupply.com/blog-2/chimney-pipe-installation-through-a-flat-ceiling/)

 

[robman]

Thanks for another speedy reply and the links. So I guess it is important to have the grille across the entire top as opposed to only having a 30" wide register in the 48" wide alcove. I was thinking of this register (https://www.reggioregister.com/metal-scroll-grille-model-832.html). The alcove will be completely enclosed in cement backer board. My other question is why use the double wall from the stove as opposed to from the box as shown in the video? Is with the size of our alcove, and it being tiled etc, is there not enough room for it to be safe?

Thanks again

Rob

 

[robman]

Hi again
I just realized I was not really clear enough with the single wall question. I was looking at a bunch of selkirk stuff earlier and it seems like the kit they sell (https://www.amazon.com/dp/B0009STHVG/?tag=hearthamazon-20) is made fr the single wall to go up to the attic connector piece, which is also shown in the rockford video. I think this kit probably makes sense but don't know if it is available for steeper roofs.

Thanks again

Rob