Woodstove Floor Protection

[John@fam]

I just installed a Jotul F500 Woodstove replacing an older Jotul Alpha. The stove sits on 12”X12”, 5/16” thick Porcelain Tile. Under the tile is ¼” Hardibacker Cement Board which is over a subfloor of ¾” plywood and ½” plywood attached to 2X10 joists 16” OC.

When I “crank” up the F500 the porcelain tile gets very hot which it never did with the Jotul Alpha. The tile under the stove is hot enough that I am concerned about combustion of the plywood under the flooring and/or damaging the porcelain tiles. Of course, my main concern is the possibility of starting a fire beneath my floor. I attched the heat shield that comes with the stove and it cut the heat transfer to the floor considerably but there are "hot spots" on the tile near the rear of the stove.

Question: Do I need to or should I place the new F500 on a hearth pad to insure our safety or is the current configuration adequate? Thank you.

 

[begreen]

Welcome John, I appreciate your concern. Unfortunately Jotul's documentation goes from simple ember protection in the beginning of the manual to full insulated hearth build at the end of the manual (building your own instructions.) That makes exact recommendations harder.

Adding the heatshield was a good plan. Check the hearth temps with an IR thermometer or at least your hands once the stove has been running 24/7. If you can hold your hands for a few seconds on the hearth, it is probably pretty safe and under 130 degrees. The temp where it starts to get dicey is over about 170 degrees. At that temp you would not be able to hold your hand there without a possible contact burn.

 

[John@fam]

Thanks for your reply Gentle Giant.
Based on your comment, after running my F500 24/7 if the temp does goes over 170 degrees I should consider adding a hearth/floor pad? If the temp is equal to or less than 130 degrees then it is OK not to add anything addl to the hearth? In short, my goal is not have the plywood below the Hardiboard & tile combust. Thanks again. P.S. What is IR thermometer?

 

[Backwoods Savage]

Welcome John.

IR = Infrared.


John, you could also add another heat shield that you can just lay on top of the tiles.

 

[begreen]

With the bottom heat shield, the stove only calls for ember protection in the beginning of the manual. If you are uneasy about this, then redoing the hearth to a higher specification certainly wouldn't hurt anything.

An IR (infrared) thermometer reads surface temps via a laser beam. It works well for spot checking different parts of the stove, walls and hearth for their current temps. A good one should read up to at least 1000 deg.

Here's an example.
http://tinyurl.com/yc8h8xz

 

[CarbonNeutral]

With the bottom heat shield, the stove only calls for ember protection in the beginning of the manual. If you are uneasy about this, then redoing the hearth to a higher specification certainly wouldn't hurt anything.

An IR (infrared) thermometer reads surface temps via a laser beam. It works well for spot checking different parts of the stove, walls and hearth for their current temps. A good one should read up to at least 1000 deg.

Here's an example.
http://tinyurl.com/yc8h8xz

From my reading of the manual, the bottom heat shield is needed for alcoves only - without it, there is still no mention that you need more than ember protection? There is this section about the bottom heatshield:

A bottom heatshield has been specifically designed for the
Jøtul F 500. It is required in all alcove installations. Use of
the bottom heatshield does not affect the floor protection
requirements discribed on page 9 of this manual. No other
type of heatshield may be used on the bottom of the
Jøtul F 500.

Interestingly I found a different version of the Jotul manual here:
(broken link removed to http://www.northweststoves.ca/pdf/jotul-wood/m-oslo-2.pdf)

The bottom heatshield text is the same (apart from page numbers) in each version I have. However,in Appendix A, there is this in the other version linked:

For the Jøtul F 600 woodstove requires floor protection with a
minimum insulating r value of 0.5.
Alcoves require an r value of 1.6.

The bit about the F600 is new/old (depending which is the most recent pdf). Good job Jotul, add a statement about the F600 to a F500 manual. Hopeless.

 

[John@fam]

Dennis/Gentle Giant: Our older Jotul was on a hearth mat in a room that had a vinyl floor for 30 yrs. Last yr we replaced the vinyl with the tile, removed the hearth mat & the Jotul Alpha looked nicer without the hearth & the room looked bigger & "cleaner" without the hearth eating into the living space. I really don't want to have to go back to a hearth & that is why I am trying to figure out if I can safely get away with the current, new configuration. The Alpha virtually did not dispense any heat downward on the floor & I was surprised at how much hear the F500 generates. It is clearly a better stove but I never anticipated I'd have to reconcider the hearth again.

I will ck the link for an IR thermometer.

Thanks for your comments & interest.

 

[John@fam]

BeGreen:

I went to the link you gave me for the other F500 manual & that manual, as you state says the minimum insulating R value for the floor is 0.5 which is what I need to make an intelligent decision. This requirement is not stated in the manual that came with my stove. I found the R value of the Hardiboard @ 1/4" to be 0.13 & I am sure the 5/16" tile is negligible & will not make up the difference. Therefore, since I am apparently way below the minimum I have to come up with at least .37 of R value for protection. The manual you connected me to is very helpful. I appreciate it. I saved it & will read it to see if there is any other info I should be aware of.

Therefore, unless I am missing something, I believe I have to add a hearth pad to protect ourselves from potential fire. So much for the clean open space we enjoyed on the new tile floor for 1 season with the Alpha. Thanks BeGreen for the technical data. From BeSafe!

 

[begreen]

Actually that was carbon neutral who posted the 2nd copy of the manual. It is an older version. They updated it around 2006?

For peace of mind, if you want a project now, replace the hearth with a stock pad or a homemade one with 2 sheets of 1/2" durock or wonderboard (get the pure cement board not the new gen stuff). Then tile on top of that.

Or poll our current F500 owners and ask what temps they have seen on their hearths with the bottom heat shield.

 

[CarbonNeutral]

https://www.hearth.com/talk/threads/31678/


some more f500 owners - split on not hot vs. hot, plus an implication from one that the heat shield is standard, not optional?

 

[CarbonNeutral]

Actually that was carbon neutral who posted the 2nd copy of the manual. It is an older version. They updated it around 2006?

For peace of mind, if you want a project now, replace the hearth with a stock pad or a homemade one with 2 sheets of 1/2" durock or wonderboard (get the pure cement board not the new gen stuff). Then tile on top of that.

Or poll our current F500 owners and ask what temps they have seen on their hearths with the bottom heat shield.

And they say the f600, so who knows that that really means.

 

[CarbonNeutral]

And there's this:

https://www.hearth.com/econtent/index.php/forums/viewreply/456982/

 

[begreen]

Thanks for the links! Will be curious to see how your hearth temps are.

 

[CarbonNeutral]

https://www.hearth.com/talk/threads/31678/


some more f500 owners - split on not hot vs. hot, plus an implication from one that the heat shield is standard, not optional?

To clarify, for completeness, I unpacked my Oslo F500 today - bottom heat shield was standard - I will be installing it even though I'm not in an alcove with my install

 

[Brian VT]

Just a quick thought...
Being cheap, I didn't want to buy a bottom heat shield for my used Resolute. The OEM one is a metal sheet that hangs from 4 bolts below the stove.
I unrolled/flattened a section of stove pipe and set it on 4 bricks beneath the stove. It accomplishes the same job. You might do something like this
in addition to what's there now and, hopefully, keep the tile temps. down ? Air is insulation.

 

[firefighterjake]

I specifically contacted my local Jotul dealer who in turn called Jotul to find out if there was a specific R value requirement and the verdict that came back was a resounding no (well maybe it wasn't resounding, but it was a "no R value requirement needed" answer).

I don't remember the exact numbers, but I "shot" my hearth last year with the IR gun (as well as taking temperature readings of my cats, wife, etc.) and as I recall the temps were not all that high . . . but you can do as BeGreen mentioned and do the "hot hand" test.

I believe the bottom heat shield is now pretty much standard with the Oslo . . . the rear heat shield (which I bought) is optional.

So in summation . . . I think you'll be OK with a non-combustible hearth which you now have . . . but if your insurance company or fire inspector wants to see listed floor protection (i.e. a commercial built hearth or 1/2 inch listed Durock) you may need to build anew . . . or conversely if you want to err on the side of safety and realize that unless you redo the hearth you will worry about this all winter long you may wish to redo the hearth.

If you do redo the hearth you can do as BeGreen suggested and go with two 1/2 sheets of the listed Durock (old stuff, not the new) over the plywood and it would only put you another 1/2 taller . . . perhaps more than you would like . . . perhaps just enough to be a toe-stubbing nuisance . . . or perhaps short enough to not mind.

 

[CarbonNeutral]

Considering that most 'informed' buyers will go to the manual prior to purchase, would it be too much of a stretch for Jotul to spell out clearly the r-value needed/not needed, the fact that the bottom shield is standard, and how to install it (ok, it's not difficult, but still....) - even if only to sell more stoves....

 

[John@fam]

BeGreen & everyone who responded.
I spoke with a Jotul Dealer who was also previously an engineer with Jotul. The Dealer referred to page 8, Section 4.1-Floor Protection of the F500 Manual: “Floor protection under the stove must be constructed of a non-combustible material for radiant heat, sparks and embers.” Jotul does not mention an R value requirement since the only requirement is that it be “non-combustible” unlike the F600 which states an R value of .5 since it is a bigger stove. If the surface below the F500 is non-combustible (porcelain tile in my case) then it meets the requirements. My concern was with the plywood which is the third layer down (tile, ¼” Hardibacker, plywood, 2 x 10 rafters). When I initially started running the stove I did not install the bottom heart shield which come standard. When I experienced how hot the floor got I attached the shield and the floor has gone from hot to warm except for in front of the stove which gets “hot” when the stove temp gets near 400 degrees.
The Dealer stated that even though I found the floor directly in front of the stove to be very hot to touch compared with the floor below my old Jotul Alpha, it should not be a concern. In other words, because the floor is hot to touch does not signify danger/concern. According to the Dealer, for the plywood below the tile and Hardibacker to combust the temperature would have to exceed 207 degrees which is boiling point or the point at which all moisture is sucked out of the wood and the potential for igniting is increased. At 325 degrees the plywood would combust. I will take advice from this Forum and get an IR Thermometer but I am confident the temp gets nowhere near 200 degrees. My goal aesthetically is to not have a hearth and I believe I am OK with the current configuration. The F500 sits in an open room on porcelain tile with no obstruction. The room looks larger, neater and cleaner with no hearth. I am going to monitor the stove closely and will still continue my due diligence to make sure the current floor situation is safe. I appreciate everyone who responded and hope that my research helped the Forum in some way. Please don’t hesitate to respond since my number one concern is that my stove performs safely. Regards

 

[Wet1]

I personally would be concerned about a floor that was hot (not warm) to the touch if I knew there were combustibles right under the surface... regardless of what the manual or anyone else said. I would consider at least adding a small hearth mat (or something similar) in front of the stove to provide more protection.

 

[John@fam]

Thanks Pyro. I am going to be 100% sure the current configuration is safe but I am inclined to put at least a thin pad down since I feel the same way you do. I'll let you know the results. Regards

 

[johnn]

Provided memory serves me well,,,i thought i had read through the "Chimney Sweep"`s, answer and question section of this forum,,,that ul listings and testing far exceed the normal operational conditions.. So much that they never have to recall data and change requirtements,,I believe it was mentioned that it would take in excess of 500 degrees for spontaneous combustion to occur through heat transfer. This however in no way would wave the requirements stated by the manufacturer to maintain,,in order for your insurance company to be cooperative. It certainly seems that each model of any manufacturer should have readily available literature,,sorry for your trouble,,glad you found the forum!!You might double check that info in the chimney sweep section?

 

[John@fam]

Thanks FHS, I'll check the "Chimney Sweep".

 

[firefighterjake]

John@fam . . . I was thinking of you just the other day and I was a bit curious . . . I had just cleaned out my stove and had the stove running most of the day and it was going strong so I used my IR gun to check temps . . . and I was a bit surprised to find that while most of the hearth was 100-130 degrees or so, there were a few spots on the right hand side that actually were 150-180 F.

I noted these temps and then rechecked yesterday after getting the stove up and running . . . this time around the temps were lower in the places where the temps had been high before. It's just speculation on my part, but I think the reason for the higher temp in that one area was two-fold: first I tend to push most of the wood when I load the stove over to the right hand side of the stove . . . the stove top temps typically reflect this . . . and second: since I had just cleaned out the firebox there wasn't as much ash in the firebox vs. when I fired it up yesterday I purposefully left more ash in the bottom which I believe had an insulating effect.

In any case, as I mentioned in the first post, according to the Jotul dealership and my manual (and now confirmed by you) you're OK with your set up . . . but in my own case I opted to build in a little more R value, but that's just because I'm a "worrier" who tends to over build.