Accentra insert - OAK install through back of fireplace

[notch]

Hello fellow pellet burners. Today I took the plunge and installed an OAK on my Harman Accentra insert. Been meaning to do this for about two years now, but between the money for the OAK parts, the cost to rent a wet core drill rig and some serious consternation about coring a hole in my fireplace, it took a bit longer than expected. I had considered putting the intake through the block-off plate above the smoke shelf, but I really wanted to seal the flue liner at the top and bottom. Plus, running a three inch pipe 25 feet to the top of the chimney was just too long a run. The only alternative was going out through the back of the firebox, as I have an external chimney on the gable end of my two story colonial. Out the back is less than three feet from stove to outside, so with a three inch vent pipe there should be no resistance. I didn't really want to put a hole in the firebox, but I figured I'll never go back to burning wood in the fireplace, and if I move I'll just save the slug and mortar it back into the hole if the new owner doesn't want the stove. I know, who wouldn't? .

I considered buying a diamond core bit and dry drilling the hole, but the bit people said clay brick was too hard for dry drilling. So, I did a little research and found that the Hilti DD150 wet core rig, available for rent ($115 for the rig and a 3 inch bit for four hours) from HD, would be the best tool for the job. The only issue with the rig was that I could not hold it while drilling the hole - it was just too heavy. I thought about drilling a hole for an anchor bolt to use the mast that came with the Hilti, but I didn't want to put any more holes in the chimney, so I stacked up some platforms to get it to the proper height. I used my workmate with the vise top, which was perfect as the core bit sat in the space between the two wooden vise jaws and kept the drill steady as I started the hole. Once drilling, it took about 5 minutes to get through two courses of clay brick. When I broke through to the firebox, a couple cups of red clay slurry got splashed all over everything, but a couple towels and a few minutes later and all was dry.

I had bought a three inch white vinyl dryer vent wall vent with a 11 inch tail from HD ($7). I took out the damper flap, and wedged in some 1/4 inch hardware cloth to keep the vermin out. I thought the 11" tail would be too long, but as it turns out it was barely enough. Once inserted, there was about one inch of the tail protruding into the firebox. I sealed the top and sides of the wall vent with some silicone to keep any rain from getting behind it and into the hole. Not really worried about it getting into the firebox, but felt it best to keep it as dry as possible. I then cut a hole in the trellis and hung that back on the chimney. I hope the giant rose bush that had been covering the trellis grows back, as I had to cut it way back to remove the trellis.

I bought some three inch aluminum flex vent, and attached the stub on the sub-frame to the tail of the wall vent, then sealed the connections with high temperature RTV silicone. I used worm-drive hose clamps to connect the bottom of the snorkel to the intake stub on the stove, and the job was done. All told, it took about four hours.

Over the last couple years I really grew tired of listening to the combustion fan run on and on long after the fire was out in the pot, knowing that all that warm air being sucked out of my house was being replaced with cold outside air that was making it drafty and would also need to be heated. I suspect that the fan will not run as long after the fire is out in the pot with an OAK, as the cold outside air should cool down the inside of the stove quicker. If all goes as planned, it'll be less drafty, I'll burn less fuel, and won't have to listen to the combustion fan as much.

Based on the weather forecast, I finished up just in time as it is supposed to get much colder later this week (it was 65F here today). I've been burning a little oil the last two weeks or so, just waiting to finish the OAK install before firing up the stove this year. Back in September I loaded up on 3 tons of Somersets when they showed up at my local Lowes, so I am ready for the winter.

I'll post back in a few weeks with some observations on whether there is a noticeable difference with the OAK.

 

[Lake Girl]

Hilti makes some very impressive equipment but the quality is reflected in the price. Glad you took the jump on the OAK and keep us posted on differences noted

 

[Wilbur Feral]

A very impressive effort and result. Nice work!

 

[tiger]

Very impressive. After all these months, via context I figured out what OAK stands for, and was curious. I was wondering if the installer of my insert installed such a thing -- looking at these pictures, no and definitely no.

I'd like to " avoid the draft" but doubt I would duplicate this -- for one thing, the other side of my fireplace is now in my tight, added-on garage and the vent cover would be very close to my car. Can an OAK be routed in from underneath or some other direction, or only from the back?

I happen to have a diamond core bit, but the type for fitting to an angle grinder thus too short -- and 4" not 3". Never the right tool for the job...

 

[tjnamtiw]

You do know that the OAK piping is supposed to be non-combustible, right? While most of it is contained in the brick and inside of the fireplace, I wonder if an insurance company would be petty enough to find that as a non-conformance I think I know the answer to that one.

 

[fmsm]

you can always run up the chimney and use a cap like this. I did and it works great

 

[F4jock]

Hello fellow pellet burners. Today I took the plunge and installed an OAK on my Harman Accentra insert. Been meaning to do this for about two years now, but between the money for the OAK parts, the cost to rent a wet core drill rig and some serious consternation about coring a hole in my fireplace, it took a bit longer than expected. I had considered putting the intake through the block-off plate above the smoke shelf, but I really wanted to seal the flue liner at the top and bottom. Plus, running a three inch pipe 25 feet to the top of the chimney was just too long a run. The only alternative was going out through the back of the firebox, as I have an external chimney on the gable end of my two story colonial. Out the back is less than three feet from stove to outside, so with a three inch vent pipe there should be no resistance. I didn't really want to put a hole in the firebox, but I figured I'll never go back to burning wood in the fireplace, and if I move I'll just save the slug and mortar it back into the hole if the new owner doesn't want the stove. I know, who wouldn't? .

I considered buying a diamond core bit and dry drilling the hole, but the bit people said clay brick was too hard for dry drilling. So, I did a little research and found that the Hilti DD150 wet core rig, available for rent ($115 for the rig and a 3 inch bit for four hours) from HD, would be the best tool for the job. The only issue with the rig was that I could not hold it while drilling the hole - it was just too heavy. I thought about drilling a hole for an anchor bolt to use the mast that came with the Hilti, but I didn't want to put any more holes in the chimney, so I stacked up some platforms to get it to the proper height. I used my workmate with the vise top, which was perfect as the core bit sat in the space between the two wooden vise jaws and kept the drill steady as I started the hole. Once drilling, it took about 5 minutes to get through two courses of clay brick. When I broke through to the firebox, a couple cups of red clay slurry got splashed all over everything, but a couple towels and a few minutes later and all was dry.

I had bought a three inch white vinyl dryer vent wall vent with a 11 inch tail from HD ($7). I took out the damper flap, and wedged in some 1/4 inch hardware cloth to keep the vermin out. I thought the 11" tail would be too long, but as it turns out it was barely enough. Once inserted, there was about one inch of the tail protruding into the firebox. I sealed the top and sides of the wall vent with some silicone to keep any rain from getting behind it and into the hole. Not really worried about it getting into the firebox, but felt it best to keep it as dry as possible. I then cut a hole in the trellis and hung that back on the chimney. I hope the giant rose bush that had been covering the trellis grows back, as I had to cut it way back to remove the trellis.

I bought some three inch aluminum flex vent, and attached the stub on the sub-frame to the tail of the wall vent, then sealed the connections with high temperature RTV silicone. I used worm-drive hose clamps to connect the bottom of the snorkel to the intake stub on the stove, and the job was done. All told, it took about four hours.

Over the last couple years I really grew tired of listening to the combustion fan run on and on long after the fire was out in the pot, knowing that all that warm air being sucked out of my house was being replaced with cold outside air that was making it drafty and would also need to be heated. I suspect that the fan will not run as long after the fire is out in the pot with an OAK, as the cold outside air should cool down the inside of the stove quicker. If all goes as planned, it'll be less drafty, I'll burn less fuel, and won't have to listen to the combustion fan as much.

Based on the weather forecast, I finished up just in time as it is supposed to get much colder later this week (it was 65F here today). I've been burning a little oil the last two weeks or so, just waiting to finish the OAK install before firing up the stove this year. Back in September I loaded up on 3 tons of Somersets when they showed up at my local Lowes, so I am ready for the winter.

I'll post back in a few weeks with some observations on whether there is a noticeable difference with the OAK.

Boy! After reading that did I ever luck out! My fireplace clean out door opens into the garage. Less than three feet to the stove's air intake. Insert seals off the room and all I do is leave the clean out door open. Instant OAK!

 

[briansol]

The 2-story cap is where it's at.

and yes, dryer vent is not an acceptable form of piping for code or safety.

clearance to burnables is also not acceptable (the trellis on the brick)

 

[Skier76]

you can always run up the chimney and use a cap like this. I did and it works great

I had not idea that existed. I'm currently running an insert without an OAK in a masonry fireplace opening. That caps looks like it would fit the bill. Do mind sharing what the material costs were for that? It looks like I would just need the cap and about 25' or so of 3 flex liner.

 

[tjnamtiw]

I too use my fireplace cleanout door outside for my OAK on one stove. I ran a flex from the stove into the cleanout in the floor and sealed it off with fiberglass. As to the OAK out the chimney, that cap is interesting but isn't there supposed to be a separation in heights between the intake and exhaust with the intake turned down? Also, the thing that keeps me from running flex OAK all the way up the chimney is thinking about when the stove is shut off on cold days. Can you imagine the cold, dense air flooding DOWN that OAK and into the house? Quads aren't sealed worth a crap.

 

[fmsm]

I had not idea that existed. I'm currently running an insert without an OAK in a masonry fireplace opening. That caps looks like it would fit the bill. Do mind sharing what the material costs were for that? It looks like I would just need the cap and about 25' or so of 3 flex liner.

Here's a link to the cap and OA pipe for just over $300. Pricey but worth it in my opinion. http://www.homeclick.com/m-and-g-du...WhPX0d41Yehor9e3cYa7SDpp0KO_R2fQJBoCoPXw_wcB#.

 

[tjnamtiw]

Here's a link to the cap and OA pipe for just over $300. Pricey but worth it in my opinion. http://www.homeclick.com/m-and-g-du...WhPX0d41Yehor9e3cYa7SDpp0KO_R2fQJBoCoPXw_wcB#.

That's with aluminum flex for gas fireplaces.

 

[Skier76]

Thanks guys.

 

[Big E]

Without oak, won't flames and hot embers blow into my house, should burn-back ever happen?

 

[briansol]

Possible, yes.
reality, it's probably not flames or embers, but rather hot smoke as in the case of a power failure, the exhaust blowers stop, the fire is still going, vacuum is lost.... effectively, it's exhaust at this point, so that's why the intake piping and thimble and clearances should be similar to exhaust for ultimate safety.

The heat is the biggest threat. Without a pipe, the heat exists the stove right there, and you can/will get smoke in the house. Assuming you have enough wall clearance, the heat factor should be ok.

 

[Lake Girl]

You do know that the OAK piping is supposed to be non-combustible, right? While most of it is contained in the brick and inside of the fireplace, I wonder if an insurance company would be petty enough to find that as a non-conformance I think I know the answer to that one.

Plastic hood outside? ... I wasn't paying attention; good catch tjnamtiw.

 

[tjnamtiw]

Plastic hood outside? ... I wasn't paying attention; good catch tjnamtiw.

Not just the plastic hood but the 'vinyl tail' that extends into the fireplace onto which he hose clamps the metal flex.

 

[tiger]

you can always run up the chimney and use a cap like this. I did and it works great

Sounds great -- in retrospect. Alas, in February when they did the install, I had never heard of OAK and the dealer didn't bring it up, but they did require (for diameter purposes) that the rip out the metal liner what was working fine for the wood burning insert and install a new one. This OAK solution would be a third liner this year.

 

[fmsm]

That's with aluminum flex for gas fireplaces.

My bad, I probably shouldn't try to work and cruise the forum..... The cap (stainless steel) is ok, and the aluminum flex is fine for the OA, just need the proper vent pipe.

 

[tjnamtiw]

For my stoves, the OA termination must be at least 12" below the exhaust termination. Nothing is mentioned in the description about this.

 

[fmsm]

It isn't 12 inches lower, it is separated by a solid stainless steel shelf (the exhaust exits in a compartment above the intake) creating a separation. This setup may not work for you.

 

[tjnamtiw]

From the Harman P35i manual >
''
1. Make a determination of where you want to draw
the outside air from. Here are a few options.
a. Punch a hole through the rear of the
fireplace and exterior wall. Rigid pipe or flex
pipe could be used.
b. Use the chimney or chase as a conduit for
outside air. The exhaust liner must be run the
full length of the flue. When creating your steel
plate to seal the damper area Make another
3 inch hole for the outside air pipe. Install a
short run of pipe from the mounting frame
through the sealing plate. Then install the
chimney top extension kit, item #1-00-674104
at the top of the chimney. This is slotted to
allow fresh air into the chimney or chase.
2. Secure the outside air supply pipe to the stub
on the mounting frame using a minimum of two
fasteners.
3. If running the supply pipe direct, install the outside
air cover weldment #1-10-09542 to keep birds or
rodents from entering the supply pipe.
4. Keep the intake a minimum of 4 feet (1.2 m)
below the exhaust termination.''

 

[fmsm]

My OAK was installed by a Harman dealer when he installed my stove, Harman themselves "blessed" the setup as he wanted to cover his ass.

 

[tjnamtiw]

Interesting. I guess they don't read their manuals. I hope they didn't use the aluminum ducting that came with the cap.

 

[fmsm]

ducting did not come with my cap. Stainless flex rated for multi fuel for the exhaust and aluminum for the fresh air.