Hearth Installation

Back in October we had to make a decision. Replace the thin firebrick veneer in our manufactured fireplace or consider replacing it. We like the fireplace but frankly, we were getting tired of it, while it looks pretty it burns  a lot of wood with minimal heat contribution to the house. Last winter neither of our heatpumps could really keep up with the temperatures outside, even on modestly cool days. We replaced the upstairs heat pump this spring at cost of about $5700 but we couldn't afford to pay the same for the downstairs unit. So we headed off to town and did some shopping around at a couple of stores.

It seemed that if we could find the make and model of the old fireplace we might be able to buy the proper firebrick sheets otherwise we needed to buy generic material and cut it down to size. Both stores we went to estimated approximately the same price for the material, not cheap but not super expensive. This would get the fireplace ready for another year (after getting the chimney cleaned of course) but we would still be at the same problem. Lots of wood burned, very little heat.

We explored the alternatives, based on our existing chimney and zero clearance manufactured fireplace our alternatives were:

1.  rip out the existing fireplace and chimney and put in a new chimney with proper chimney pipe for a wood burning stove and close in the existing openning and place stove in front. That was a pretty pricey option as the chimney alone with all its pieces etc added up to > $2000 and that didn't include a stove.
2. rip out the existing fireplace and put in a new one that was a bit more energy efficient. Still a substantial amount of money - perhaps the same amount as option #1 or even more depending on variables.
3. put in a chimney liner and route it out through the front of the fireplace and place a hearth heater type "insert" infront of the fireplace - approximately $3100 installed (liner, stove and installation).

Depending on which store we went to we got slightly differing opinions on option #3 with one suggesting that we could line the chimney and put a standard woodstove in front. In the end we chose option #3 with the Regency H2100 Hearth Heater purchased and installed by Wooden Sun in Charlottesville, VA.

I chose to take on the task of upgrading the hearth myself as I wanted to alter its appearance. The original was black slate and it really didn't look that great in my opinion. I wanted the hearth to match more of the stone work of the fireplace. I also assume that because the original fireplace was a zero clearance manufactured fireplace, the existing hearth only needed to be non-combustable as it was just black slate about 1" thick glued to the engineered hardwood floor with a ton of construction adhesive and then grouted. The H2100 Hearth heater specs stated that the floor protection must be R1.1 or greater. So my first step was to do a bit of research.

Turns out that stone itself has basically no R value, even ceramic tiles have a limited R value on their own. Concrete backer board actually seems to have slightly more R value then does 1" of stone, but still it also provided limited R values. In order to get the values needed without building a 12" thick hearth  I needed to start with a 1/2" Micore base. 1/2" Micore alone provides the full R value required for the hearth heater. Micore is a fairly soft material and is actually used as acoustic panels as well. You can get it in 4' x 8' sheets but its hard to come by locally. I wound up buying two 6' x 18" panels at ~$40 per panel.  All the sites I looked at on the Internet suggested that it wasn't adviseable to simply place stone directly ontop of the micore bur rather put 1/4" or 1/2" cement backerboard over the micore and then the stone. The combination would exceed the requirements by about R 0.2 or so which is actually a good thing - better too have more insulative value then not enough.

Chandra and I went out to Charles Luck Stone center  in Charlottesville and bought new flag stone - five 18" x 24" x 1" and two 24" x 24" x 1". We chose a light tan colored rock that was rough but seemed to match the colors in the stone veneer on our existing fireplace. We picked up the Micore panels from Wooden Sun and 1/2" cement backer board from Lowes as well as mortar, screws and some construction adhesive. With everything in place we got busy starting on Friday Oct 29th. We had to be completely done the project before the installation on Wednesday Nov 3rd. Lots of fun :-)

To get rid of the original hearth, I first tried to pry up the existing stone but that didn't work very well. The construction adhesive was so well attached to the engineered hardwood floor that prying it up resulted in the flooring coming up with it. While we wanted to go down to the oriented strand board subfloor, I didn't want to wreck the whole floor in the process.  Plan B involved getting out the circular saw, using my oldest and most worn out blade and setting it so that running the saw on top of the slate with the blade about 1/4" out from the stone it cut just deep enough to cut through the hardwood flooring but not the subfloor. Then it was a simple matter of popping up the stones with the flooring still attached.

Then using a straight edge and skill saw, I carefully straightened the cut line between where the stone would end and the hardwood would begin making sure once again only to cut the hardwood and not the subfloor. Because the hearth heater sits in front of the fireplace opening, we also needed to extend the hearth out in front by another 20" or so in the middle where the stove would sit. We went out 24" based on our understanding of the clearances and went 48" wide to match the stone we bought. We probably could have gotten away with only 18" x 40" after seeing the stove installed. But its actually better to extend more in front and the sides then the minimum requirements. Again we simply used straightedge and skill saw to cut the flooring and then pried it up. We scrapped off any remaining construction adhesive and vacuumed up the dust and small stuff.

With the subfloor exposed we cut down the sheets of Micore to fit and then using construction adhesive and screws we attached it to the subfloor. We ran out of micore on the far left edge so I patched in using a piece of 1/2" cement board. Since this is well outside of the "heat" area and way outside the required 6" on either side of the stove I don't believe this constitutes any kind of problem.

With the micore in place I put down the 1/2" cement backer board and screwed it down. Then we laid out the stones and figured out the arrangement to best match color and texture. 

We had to trim the two end stones and then trim 4 of the stones to work around the veneer. I bought a DeWalt Diamond masonary blade for the skill saw. I was amazed at how easily it cut through the stone. I'll be honest, I've had the saw work harder cutting through oak boards then it took to cut the stone.
We set the stones in a 1/2" of mortor using a trowel with 1/2" x 1/2" notches. After it dried for 48hrs we grouted it and then let it sit another 36hrs before we sealed it. We got the sealer on and dried just in time for the installation. Not much time to spare waiting the required times between steps.

The final installation came out really nice. They closed off the front of the fireplace with  a piece of sheet metal. The stove is about 1-1/2" in front of the openning.  I still need to finish off the trim around the stone to hide the floor/stone line. Being the first time I've ever done stone work, I think this came out pretty nice.

We've been running it over the past month, mostly during the evenings and overnight to keep the heat pumps from kicking in. It really warms up the house amazingly well for such a small box. It heats the lower floor, especially the living room and kitchen but we have the fan on the air exchangers running to circulate the air into the rest of the house. Upstairs it gets up to 74 degrees in our bedroom and probably around 76 in the loft (directly above the living room). The stove came with a fan that circulates air around the outside of the firebox which really contributes to warming the air. I haven't seen an electric bill yet, but I'm guessing we'll see a decrease in it relative to last year. For the first time since we bought the house I can honestly say that it is actually warm on cool days.