Hearth Extension Thickness for wood buring insert

[RingDing]

Hi,

I had a Lopi Freedom Bay insert installed in my masonry fireplace a few years ago. The house is about 60 years old and the hearth is level with the floor. I’ve never had a problem but have always been concerned about the hearth extension.

The Freedom Bay sticks out onto the hearth extension about 4.5”. The extension is mortar about 3” thick and supported with ¾” wood boards as can be seen from the basement.

I always wondered if there is a clearance to combustibles issue with this set up. The owners manual doesn’t specify a minimum hearth extension thickness or R value other than it should be non-combustible and at least about 0.018” thick. The diagrams show the hearth extension to be that portion beyond the fireplace opening. It doesn’t show that it’s only that portion beyond the face of the insert opening.

So are they saying it’s ok for the 4.5” of the insert that sticks out can rest on wood flooring if there is a piece of sheet metal protecting it? Seems insufficient but it’s what it says. If that set up is approved then I should be in good shape.

By the way, the Freedom bay’s combustion chamber is about 1.5” above the insert floor to allow air movement around the firebox. But the insert floor does get very hot. The wood framing in the basement only ever got warm to the touch. I drilled a small hole in the framing so I could feel if the masonry hearth extension bottom ever got hot. It never really did except for one time it got hot.

The dealer did the pre site visit and the install. I called the manufacturer a while ago but never was able to talk to the right people. They couldn’t clarify things but kept saying it needs to be installed in an approved masonry fireplace.

I know we all have our opinions about this. Seems like an insuffiecint set up, but anyone know about the specs? Thanks.

 

[Lasher]

I am going to be installing an Olympic insert and have the same heart requirements.

0.018 inches thick or 26 guage

To me it sounds like a piece of sheet metal will meet the requirements. I looked at a ton of insert manuals when trying to decide to put the used stove I got in, or buy new one that would not need an extension. Most of the other manuals require a R rating, which is a lot more than 26 guage steel.

Maybe some one else will chime in, but if the manual states that is all that is needed, then that is what I am going to do. By the way, I only need about 3-4 inches more to meet the 16 inch requirement in front of the insert. The rest is thick marble. My plan is put down a 26 guage sheet metal and then cover with a hearth rug.

 

[RingDing]

I have been using sheet aluminum in front of my insert to get the required 16". Works great. The wood floor below it never even comes near hot.

 

[webbie]

Ring,

I assume your heart is flush to the floor? Both the inside and the extension?
Also, you say 3" thick....is there brick or tile on top of that?

It sounds like the manual is saying that....what you said! BUT, I am suspicious of this, and many manuals are not accurate and up to date. Common sense would say that a firebox only 1.5" above the hearth AND with a large radiating glass door would get vastly hotter than what they are alluding to.....I don't buy it, and I don't think anyone here who has burned a stove for a long time would. The only time the "just non-combustible" thing works is when a stove is very high up - like on a pedastal, or has a large air space and a bottom heat shield.

So I think you are correct to be concerned. Is it going to burn the house down tomorrow?? Not that I suspect, but if you used that unit very hard on a constant level I think that wood might get over the UL allowed temps.

For comparison sake, I have attached a pic of a VC Century insert (much smaller than yours), and the requirement. If anyone can explain to me why this calls for 3/8" millboard (micore, etc.), and yet the Freedom only needs sheet metal...well, I'm all ears. But it does not seem correct.

 

[RingDing]

Well, based on that diagram of the VC, I think I'm not too bad off. If I understand it right, they're saying 3/8" thick millboard is all that is required for the area beyond the faceplate of their insert. That includes a portion under the insert. Just wonder how much of the combustion chamber extends over the hearth extension.

My hearth is flush to the floor, both the inside and extension. My hearth extension (the area beyond my faceplate) is 3" thick - about 2-3/4" mortar with tile on top about 1/4". The hearth itself is built ontop of masonry foundation so that's ok.

Actually, the wood floor in front of my insert does not get hot at all. I have it covered with sheet aluminum and it works great. I lift the sheet aluminum up every now and then to check. Maybe a sheet of ferrous metal wouldn't work as well.

I think you are right. Stoves which sit high up can get away with it, but an insert resting on the floor???

A few years ago I called the Director of Technical Services at Quadrafire because their owners manual has the K-Factor and R-value specified for their inserts. I pretended like I was considering getting a Quadrafire. From what I remember, he said there was a big factor of safety among other things. I came to the conclusion at that time I was ok with my installation. In any case, there is always concern for me because I never see the specs.

Thanks.