Heat shield advice

  • Active since 1995, Hearth.com is THE place on the internet for free information and advice about wood stoves, pellet stoves and other energy saving equipment.

    We strive to provide opinions, articles, discussions and history related to Hearth Products and in a more general sense, energy issues.

    We promote the EFFICIENT, RESPONSIBLE, CLEAN and SAFE use of all fuels, whether renewable or fossil.

Sdhkenyon

New Member
Sep 13, 2021
14
Alabama
I am getting read to install a supreme novo onto a 3” thick concrete shelf which rests on a wooden cabinet about 18” off the floor. I opted to go without the pedestal and up to this point was planning to place the stove directly onto the concrete. Would like a second opinion on whether to add a hearth pad below the stove and if so whether soapstone might be a good choice. Would also welcome any advice on heat shield for the rear wall and on the wood floor in front of the stove…

current state
D481A17C-5E7D-404D-B497-C243578C9C87.jpeg
mock-up of where we’re heading:
2A2FBE63-3E92-461E-BD08-7422E9A33B9B.jpeg
 

Sdhkenyon

New Member
Sep 13, 2021
14
Alabama
I am getting read to install a supreme novo onto a 3” thick concrete shelf which rests on a wooden cabinet about 18” off the floor. I opted to go without the pedestal and up to this point was planning to place the stove directly onto the concrete. Would like a second opinion on whether to add a hearth pad below the stove and if so whether soapstone might be a good choice. Would also welcome any advice on heat shield for the rear wall and on the wood floor in front of the stove…

current state
View attachment 281953
mock-up of where we’re heading:

View attachment 281954
This is the manufacturer guidance:
1631584993129.png
 
Last edited by a moderator:
Oct 15, 2020
145
New Hampshire
I’m no professional but recently have been taught quite a bit about this.

Generally what I’ve found is, if there is any wooden structure under your hearth and extension it needs a higher R value. Concrete doesn’t do much to stop heat so you definitely need something else.

Not sure if soapstone is best because it is a heatsink.I’m thinking it will slowly heat up and then hold and let that heat out slowly into your wooden cabinet.

You may be able to get an adequate hearth pad but I’m not sure how clearances and rules change when you remove the pedestal.

Again, just sharing what I’ve been learning. One of the experts should chime in.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
25,487
central pa
This is the manufacturer guidance: View attachment 281955
They have it spelled out there pretty well. It looks like you probably need R 1.05. I believe concrete is only R. 095 per inch. So you will need something additional. Why do you need heat shielding on the wall?
 

EbS-P

Minister of Fire
Jan 19, 2019
1,206
SE North Carolina
What is your “C” distance and are your installing single or double wall? will you meet I don’t see any reason to install wall heat shield if you are meeting your clearance.

If “H” is greater than 12” you only need ember protection on the floor.
 

Sdhkenyon

New Member
Sep 13, 2021
14
Alabama
What is your “C” distance and are your installing single or double wall? will you meet I don’t see any reason to install wall heat shield if you are meeting your clearance.

If “H” is greater than 12” you only need ember protection on the floor.
They have it spelled out there pretty well. It looks like you probably need R 1.05. I believe concrete is only R. 095 per inch. So you will need something additional. Why do you need heat shielding on the wall?
Interesting. I contacted the manufacturer and they quoted the r value of concrete at .5 per inch - but I have seen a whole range of r values for concrete so not sure what to believe. If I did need to increase the r value (even just to be on the safe side) what would be a good material? Is soap stone a good solution? For the rear wall, I may get down to 9” to 10” (manufacturer guideline is 11”) in order to avoid a rafter.
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
25,487
central pa
Interesting. I contacted the manufacturer and they quoted the r value of concrete at .5 per inch - but I have seen a whole range of r values for concrete so not sure what to believe. If I did need to increase the r value (even just to be on the safe side) what would be a good material? Is soap stone a good solution? For the rear wall, I may get down to 9” to 10” (manufacturer guideline is 11”) in order to avoid a rafter.
Do they allow for further reduction with shielding?
 

Sdhkenyon

New Member
Sep 13, 2021
14
Alabama
What is your source for .095? This is the table I am seeing repeatedly referenced:
1631641072664.jpeg


.52 per inch is what the stove manufacturer quoted me - but I get the sense that they were not experts in the area of r value for concrete…. does anyone have a definitive answer?
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
25,487
central pa
What is your source for .095? This is the table I am seeing repeatedly referenced: View attachment 281965

.52 per inch is what the stove manufacturer quoted me - but I get the sense that they were not experts in the area of r value for concrete…. does anyone have a definitive answer?
It really depends upon the density of the concrete you used. The . 095 per inch is for the densest commonly used concrete. I use that because it is the safest option. If you know the actual density of what was used you can go by that.
 

EbS-P

Minister of Fire
Jan 19, 2019
1,206
SE North Carolina
My quick googling has it anywhere from 1.0-0.01 R value per inch. Looking like it depends on on the density. Bagged concrete mix by my math comes in at 130# per cubit foot. All saw that referenced as “normal” weight fore basement walls. So I think the answer there is no definitive answer. I’d put down a 1/2 micro core to the edge of the concrete (back far enough to finish the edge). and whatever on top of it to finish the look. It’s probably the only certain answer.
 
  • Like
Reactions: bholler

Sdhkenyon

New Member
Sep 13, 2021
14
Alabama
My quick googling has it anywhere from 1.0-0.01 R value per inch. Looking like it depends on on the density. Bagged concrete mix by my math comes in at 130# per cubit foot. All saw that referenced as “normal” weight fore basement walls. So I think the answer there is no definitive answer. I’d put down a 1/2 micro core to the edge of the concrete (back far enough to finish the edge). and whatever on top of it to finish the look. It’s probably the only certain answer.
Seems like a sensible recommendation, thank you. Just to make sure I’m following what you are suggesting: I will get a micore sheet as large as the stove instructions call for under the stove and place that on top of the concrete hearth. I will then put a more attractive stone on top of it (probably soapstone, but could be anything) and then will frame in the four sides with matching stone to cover the edge of the Micore. Does that seem right?
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
25,487
central pa
Seems like a sensible recommendation, thank you. Just to make sure I’m following what you are suggesting: I will get a micore sheet as large as the stove instructions call for under the stove and place that on top of the concrete hearth. I will then put a more attractive stone on top of it (probably soapstone, but could be anything) and then will frame in the four sides with matching stone to cover the edge of the Micore. Does that seem right?
That sounds like a good plan to me. It's to late now but the best option would have been to put the micore under the concrete.
 
  • Like
Reactions: Sdhkenyon

EbS-P

Minister of Fire
Jan 19, 2019
1,206
SE North Carolina
Seems like a sensible recommendation, thank you. Just to make sure I’m following what you are suggesting: I will get a micore sheet as large as the stove instructions call for under the stove and place that on top of the concrete hearth. I will then put a more attractive stone on top of it (probably soapstone, but could be anything) and then will frame in the four sides with matching stone to cover the edge of the Micore. Does that seem right?
I would probably run it as close the front edge of the concrete to insulate the framing under the concrete as is practical and looks good. Under my stove doesn’t get as hot as it does in front due to direct radiation from the window but I have an ash pan.
 
  • Like
Reactions: Sdhkenyon

Sdhkenyon

New Member
Sep 13, 2021
14
Alabama
Thanks all - appreciate all the advice. Will post a picture once it all comes together.
Follow up question after discussing with my builder. If I instead fabricated a stand to put it on how many inches tall would it need to be to achieve a r value of 1 from the air gap. I am seeing 3.5 inches online, but that’s for still air. The air here would flow through - but wondering if it would actually help me in my situation since hot air should be flowing out and up and I am trying to prevent heat from radiating down so the convection would work in my favor? Ami thinking about this right? Does 3.5 inch tall stand seem like enough?
 

bholler

Chimney sweep
Staff member
Jan 14, 2014
25,487
central pa
Follow up question after discussing with my builder. If I instead fabricated a stand to put it on how many inches tall would it need to be to achieve a r value of 1 from the air gap. I am seeing 3.5 inches online, but that’s for still air. The air here would flow through - but wondering if it would actually help me in my situation since hot air should be flowing out and up and I am trying to prevent heat from radiating down so the convection would work in my favor? Ami thinking about this right? Does 3.5 inch tall stand seem like enough?
Ask the stove manufacturer
 
  • Like
Reactions: EbS-P

begreen

Mooderator
Staff member
Nov 18, 2005
89,580
South Puget Sound, WA
An inch and a half free air space would meet the required R value.

 

EbS-P

Minister of Fire
Jan 19, 2019
1,206
SE North Carolina
was there a model with legs? Under stove requirements are different than the hearth. One could probably make the under stove R value but not the hearth R value unless the “H” is is 12 inches. Then the hearth only needs ember protection. Look again at the diagrams posted above. Seems like at 3.5 inches you still need R=0.54 hearth protection in front of stove.
 

begreen

Mooderator
Staff member
Nov 18, 2005
89,580
South Puget Sound, WA
was there a model with legs? Under stove requirements are different than the hearth. One could probably make the under stove R value but not the hearth R value unless the “H” is is 12 inches. Then the hearth only needs ember protection. Look again at the diagrams posted above. Seems like at 3.5 inches you still need R=0.54 hearth protection in front of stove.
Good point. It looks like this will be a question of whether the stove is positioned right at the edge of the concrete platform or inboard a bit. However, even if right at the edge there would still need to be ember protection for the floor 12+ in. below. The other thing to consider if this is going to be a 24/7 heater is the lack of an ashlip. This will be a messy operation without one. If the ash falls on the floor it will get tracked around the room.
 

begreen

Mooderator
Staff member
Nov 18, 2005
89,580
South Puget Sound, WA
One other thing to note is what looks like a return air vent above the stove location. That will need to be at least 10 ft away from the stove to pass mechanical code.
 

EbS-P

Minister of Fire
Jan 19, 2019
1,206
SE North Carolina
Can you cut out the framing install temporary supports if necessary, install micro core under the slab then reframe? Would this Solve all the issues? Might still have combustible trim but that could be trimmed with tile?
3” concrete R=.3 plus 1/2” micro core R=1. Total R=1.3

that covers every install shown above.

Evan
 

Sdhkenyon

New Member
Sep 13, 2021
14
Alabama
Can you cut out the framing install temporary supports if necessary, install micro core under the slab then reframe? Would this Solve all the issues? Might still have combustible trim but that could be trimmed with tile?
3” concrete R=.3 plus 1/2” micro core R=1. Total R=1.3

that covers every install shown above.

Evan
Yeah, that’s the direction I was trying to take my builder. He balked at cutting out the plywood below the concrete. It totally makes sense to me, but finding someone willing to do it are two separate things… would have to let them finish the overall project and then get someone back in to just do that part…