HEARTH PAD ? FOR ENGLANDER NC30

[westside]

I'm getting ready to build a corner hearth pad for the nc30 i just purchased and wanted to know the best materials to use in order to get the correct R-value of 1.5 that is requied for this stove . I plan on using 3 1/2 inch metal studs spaced 16 inchs on center and sandwiching a sheet of 1/2 inch micore 160 in between 2 sheets of 1/2 inch cement board. Then tile over it with 1/4 inch ceramic tiles .
Does this sound like a good set up ? Also need to know what type of cement board to use ? From what i have read here on the forums the durock is no longer listed for use on hearth pads . Would wonderboard or hardibacker be acceptable ?

 

[westside]

Thanks for the info Roberth42 . Glad to hear you're happy with your nc13 . It's spring time here in indiana so it looks like it will be awhile before i'll be enjoying my stove but it gives me all summer to get it set up.

I just got off the phone with a local department store who said the 1/2 inch hardibacker was fire rated with an r value of .20 and according to the 1/2 inch micore 160 specs it has an r value of 1.43. So that should have me covered on the r value , plus the dead air space of the 3 1/2 inch frame should add even more r value . One concern i had was if the 16 inch on center would support the weight ( 475 lbs. )of the stove. I had some short pieces left over so i added some cross braces. One other question, i plan on trimming the outside edge with wood , do you think it would be safe to only use 1/2 inch of the hardibacker or should i use 1 inch and then install the wood trim.

 

[begreen]

Good to see the additional bracing. Normally for woodstoves I like 12" OC metal studs for greater support of the backer board. The air space will contribute significantly to the overall insulation value. I don't think you need the micore, but would still double up on the cement board for increased rigidity. If you want greater protection and support, pop rivet a sheetmetal skin before screwing down the cement board.

Note, Hardibacker is not considered ideal because of its cellulose content. If you can get pure cement board Durock or Wonderboard that is better. However, they are phasing this material out in favor of their NextGen cement board which has styrofoam beads in it. How this will work for hearths is unconfirmed.

It's great that you are mocking up and taping out the hearth. From the picture it looks like the front hearth requirement of 18" in front of the glass is a bit shy. Did this get added to the final design? It looks like it.

 

[Hiram Maxim]

I think your going to see a lot of btu's absorbed by that window? hh:

 

[begreen]

Hate to say it, but that window is tiny next to the units in our house. And yes, they suck out a lot of heat, even though new and thermopane.

 

[westside]

Begreen , according to the info roberth42 recieved the nextgen durock should be ok for hearths but from all the controversy i've been reading i may just go with the wonderboard . Do you know the r value of the wonderboard ? As for the sheet metal could i use the rolls of roof flashing or is there a certain gauge of metal required ? I built the frame to allow 18 inchs in front of the stove and plan on adding another strip or two of 1/2 inch cement board all around the outside edge of frame which will give me 19 or 20 inchs clearance in front of stove.


Hiram , i orginally wanted to have the stove on the inside wall in the center of the house which would have the stove facing the window you see in the picture but the living room where the stove is measures 15' x 30' . The corner install is still only 6 ' from center of the house and has the front of stove facing cady corner the 30' length of the room . I realize the window will be a big heat drain . I had planned on cutting a piece of 1inch foil backed poly-shield foam board with an r vale of 4.4 to fit in side the window sill for use during the winter. Do you think the poly-shield will be a problem ? I'm sure it's combustible but is well past the required clearance.

 

[begreen]

The most important contribution to the R value in your design is the air space. This site says that will add R 1.01 to the system:
http://hyperphysics.phy-astr.gsu.edu/Hbase/tables/rvalue.html and
http://www.allwallsystem.com/design/RValueTable.html (Craig's chart lists it as 1.43/inch??)
Cement board is R .52 for 1" (2 1/2" layers).

The metal skin should be tight. Pop rivet it to the metal studs at least once every 8". It doesn't have to be thick, 26 gauge would be fine. I prefer sheet stock as it already wants to lay flat.

Don't worry about the window for now. When that big boy gets cranking hot, you may need to open it .

 

[Hiram Maxim]

Begreen , according to the info roberth42 recieved the nextgen durock should be ok for hearths but from all the controversy i've been reading i may just go with the wonderboard . Do you know the r value of the wonderboard ? As for the sheet metal could i use the rolls of roof flashing or is there a certain gauge of metal required ? I built the frame to allow 18 inchs in front of the stove and plan on adding another strip or two of 1/2 inch cement board all around the outside edge of frame which will give me 19 or 20 inchs clearance in front of stove.


Hiram , i orginally wanted to have the stove on the inside wall in the center of the house which would have the stove facing the window you see in the picture but the living room where the stove is measures 15' x 30' . The corner install is still only 6 ' from center of the house and has the front of stove facing cady corner the 30' length of the room . I realize the window will be a big heat drain . I had planned on cutting a piece of 1inch foil backed poly-shield foam board with an r vale of 4.4 to fit in side the window sill for use during the winter. Do you think the poly-shield will be a problem ? I'm sure it's combustible but is well past the required clearance.

I would use something to cover & reflect the heat from the window.

The one nice thing is that you could hook up "outside air intake" for combustion air from that window through the foam! ;-)