Minimum for Floor Heat Protection

[SheilaD]

We have a HiFlame (Model HF-905U) wood burning stove and be installing it in a porch with a 3/4" treated plywood floor with 10" of insulation under it.

We know we're ok with the wall clearances, but....

For the floor protection, our "tile guy" stated we could use 1/4" Hardi Backer with a 1/4" stone tile on top of it. From what I've been reading here, this doesn't seem like enough fire protection to me.

We received this from the manufacturer of the stove as far as protection goes. (I've attached a copy of what they sent.)

I'm thinking that the 11 MAY be 1.1?? Doesn't 11 seem a bit much, or am I totally misinterpreting that statement? If anyone can give me their opinion(s) and help, I would sure appreciate it

 

[Grisu]

I cannot access the manual to check what is says in there. If you have it and it is still not clear I think you would need to ask the company what the 11 really means. At 11" you are looking at a hearth with a r-value of ~13. If it is a typo and just 1.1" you will be good with r = 1.31. In any case, your "tile guy" is wrong: hardibacker + tile won't meet either requirement. This table may be helpful: https://chimneysweeponline.com/horvalue.htm

 

[SheilaD]

Thanks for the reply. Here is a link to the stove manual: https://www.manualshelf.com/manual/hi-flame/hf-905upb/instructions-assembly-english.html (hope that helps). Haven't heard back from the mfr. yet regarding the "11"number that was quoted in their reply to my email. SO.... IF it is 1.1, we would have to use THREE sheets of Durock, correct? We thought they could have meant 11mm, if so that would be right around 1/2" for protection. If that's the case (sorry for all the scenarios here, lol), could we safely get by with the 1/2" Durock and then our tile? We want to be safe and not just skate by. Thanks everyone - my brain is working overtime (THAT hasn't happened in a while - HA!).

 

[Grisu]

Thanks for the manual. It makes it even more confusing:

Floor protection under the stove must be a UL 1618 Type 1 Ember Protector composed of non-combustible material for protection from radiant heat, sparks and embers.

That would suggest the stove does not need any thermal protection under it; just tile would be enough. Is there a label on the stove? What does it say there? That UL-tag is the binding one.

 

[SheilaD]

Well, there is a metal label type thing on the back and the only reference I can find that concerns a UL number is it says "Tested to UL 1482-2010 Certified for U.S.A.". Does that help at all? I've attached a copy of the label that's on the back (same as on my original posting). Again, thanks!

 

[Grisu]

That tag is usually the one an inspector will look for. It is interesting that it seems to contradict the manual. I think you really need a clarification from the manufacturer and that should be in writing for future reference. Given that the stove sits really low over the ground you may need a relatively high hearth protection. I would not feel comfortable to just interpret the tag one way when in fact a higher r-value is required.

 

[SheilaD]

Hmmm... of course the mfr. is in China which makes things a little more difficult. I am still waiting for a reply from them on the thickness of the heat shield, etc. I will see what they say and go from there. I guess we will think in terms of having a higher "platform" than originally thought. I think we will have to use the email reply for our "writing for future reference". Thanks for all your help.

 

[Grisu]

Do you already have the stove? The Englander VL-17 is a nice little stove with ember protection only requirement, similar price point, manufactured and and also supported right here in the US.

 

[SheilaD]

Yes, we've had the stove for about a month or two and are just getting around to putting it in.

Here's what the mfr. wrote back to me when I inquired as to what the "11" meant on the floor protection question:

Hi Sheila,

Thank you for your question. It lets me recognize a printing mistake on the label.

It is not 11 minimum thickness but 1" minimum thickness. I'm sorry for this printing mistake that has made you confused.

Can you let me know what you mean by R rating? I'm sorry I don't know this.

Best regards,
Haibo

How do I explain the R rating to him/her? AND then I guess it means that we need 1" of floor protection. Hmm... what would be best to use? We already have some 1/2" Durock, so should we just stack 'em up to get to 1", or do you think that 1" could include the tile? Any help is appreciated. Sorry to be a pest...

 

[Grisu]

1" of hearth material with a k-factor of 0.84 comes to about 1.2 in r-value. I don't think it matters how you achieve that; just choose the material(s) from the table that work best for you. If you want to stay within 1" you will need some mineral board like Micore in there. Nevertheless, I would rather err on the side of putting too much protection in than too little.

 

[SheilaD]

Yeah, me too. I think we'll just double up on the 1/2" Durock since that's what we've got, and then ask our tile guy if he wants or needs to put the Hardi Backer on top of that for tile installation. If so, that may help a bit too.

Thanks for all your help. It was most appreciated. Wish us luck with the stove!!

 

[SheilaD]

Actually, now that I look at the chart from the link you provided, the Durock only has an R-value of .78 (two 1/2" sheets stacked). That isn't anything near the 1.2 R-value that you came up with. Am I figuring wrong (again)?

 

[Grisu]

Yeah, me too. I think we'll just double up on the 1/2" Durock since that's what we've got, and then ask our tile guy if he wants or needs to put the Hardi Backer on top of that for tile installation. If so, that may help a bit too.

Thanks for all your help. It was most appreciated. Wish us luck with the stove!!

I don't see how that gives you a r-value of 1.2. 1" of Durock next gen is 0.78 + hardibacker 0.2 + tile 0.02 = 1. That would be 0.2 short.

 

[SheilaD]

Yep, you're right. Just coming back here to comment again. So... 3 sheets of Durock, 1 of hardiback and the tile. That should equal 1.39 right? Then we should be good to go?
We'll be going to Menards tomorrow and picking up two more sheets of Durock so we can place two sheets side by side, three deep. Hopefully that should do the trick.

So just out of curiosity, does the minimum R-value have to be 1.2? Just wondering.....

 

[Grisu]

The formula is 1/k * thickness = r-value. You have a given k-value of 0.84 and thickness of 1". Together that equals 1.19 in r-value. With 3 1/2" sheets of Durock next gen + hardibacker you will be there.