DIY Osburn Stratford II install with forced air distribution kit

[geofox784]

Earlier this fall I started working on replacing my old builder-grade zero clearance fireplace with a new ZC fireplace. This turned into 3 months of work after discovering that the chimney chase was apparently slapped on without any codes or common sense involved.

Skip to the next post if you don't care about the chimney chase construction....

Here is what I started with:

My foot ended up going through the floor due to water damage from a leaking chase cap:

Not pictured: The whole chase was sagging away from the house with a 1" gap between the top of the chase and the rest of the house, and the insulation was turning black from excess heat. There was also almost a square foot of holes going into the attic, which allowed a significant amount of air flow into the house. Fun stuff....

The chase is unsupported from below and hangs above my driveway from the 2nd floor. Instead of using cantilevered joists, whoever built it just toed in some 2x8s to the end joist, which were cracking and sagging under the weight. How this thing didn't fall off the house already is beyond me.

After removing all the water damaged wood I welded some heavy duty steel braces to help hold it up.

I then pulled the chase back into place with some threaded rods to close the gap. Added lots of lag bolts to keep it in place.

After insulating the side walls, I also added 3/4" OSB and tied that into the house to add a significant amount of sheer strength to further support it.

With the 15' minimum chimney length, I would have had 6.5' of chimney sticking out of the top. I was concerned about poor drafting due to my high altitude (7400') and decided to extend the chase another 3.75'.

I was originally planning on just leaving the existing siding up, but discovered that the "builder" had skipped adding any house wrap or tar paper, so water was almost certainly getting in and just drying into the house. Time to rip it all off and start that over.

I had already ordered steel paneling for the extension, and decided to installing LP Smartside where I ripped off the old siding. I am planning on replacing the roof with a black standing seam roof next year, so the metal paneling should match well.

I then insulated everything and installed 5/8 fire drywall. Local codes required it, and IIRC the chimney required it as well. Even if not required, it seemed like a good practice compared to paper backed insulation hanging in there. The steel at the top is just some flashing I had left over and was not required.

Even with all the extra support, I wanted to keep the 500lb fireplace weight off the chase. I used 2" angle steel bars to support the stand from below and lag bolted them to the joists.

I had the entire thing measured out and designed in CAD. Made it much easier to confirm I had proper clearances, etc.

I am certainly no pro and most of my time was spent reading and planning, so I'd be happy to take any pros advice on anything I should have done differently.

 

[geofox784]

Choice of fireplace:
After a few months of on and off research, I decided to go with the Osburn Stratford II. My goal is to heat my entire upstairs with it, as my other source of heating is electric $$$ baseboard or gas furnace heat from downstairs flowing up.

With that goal in mind, I wanted a way to distribute the air to the far rooms instead of having cold rooms and a superheated family room. Several ZC fireplaces had forced air distribution kits, but almost all of them were clearly designed for very short distances. The Osburn forced air kit listed the longest recommend max distance at 50', which was about what I was planning.

Another option was the Valcort Lafayette II / IIs. After lots of reading about both, I can confidently say that it is virtually identical to the Stratford II, with the exception of a single door vs double. Both are made at the same factory (SBI). It was practically a coin toss deciding between the Stratford II and Lafayette IIs.

Note that the fireplace does not come with carrying handles. They are sold separately and absolutely required if you plan on moving this beast more than a few feet.

Purchase:
I purchased it from efireplacestore.com. I would highly recommend any DIYers make their purchase through them. Their pricing was competitive (and they will price match if not), but most importantly they had very helpful installation experts available to talk to answer technical questions.

Chimney Pipe Choice:
Regardless of 1" or 2" of insulation in the pipe, they all require 2" of air clearance around the pipe. Due to some strange framing during the original construction of the chimney chase, I had an equivalent of a 2x8 wall. To keep the fireplace flush with the interior wall and to avoid angles in the pipe, I needed to use the 1" pipe to maintain the 2" of air clearance.

However, all of the 1" chimney pipes, including the Duravent Duratech I used, require a ventilated roof flashing, presumably since they run hotter exterior temps than a 2" pipe. This is both required per the Osburn manual as well as the Duratech manual. This ended up creating condensation issues (see below post for a fix). If you have the room, get a 2" pipe to avoid the ventilated flashing issue.

Fireplace Install:
90% of the work was in the framing / prep work for the fireplace. To make sure the chimney chase would meet the requirements of the fireplace, I basically had to learn every step of the install of the fireplace itself. When the pro I was going to use ended up being to busy for the install, I wasn't too concerned about doing it myself since by that point I felt I knew every step of the install and had read the manual / other guides several times over. I also pulled a permit and passed rough-in inspection with no issues.

No major issues with the install, other than mis stamped letters on the (optional) fire screen door. Also, the carrying handles are held on with bolts going into rivet nuts. The rivet nuts have the bolts pre-installed from the factory and need to have the bolts removed. They were too tight and caused the rivet nuts to all spin in place. I had to jam a chisel between them and the steel paneling to hold them in place to get the bolts out.

The chimney is supported with a roof support at the top. It also passes through a firestop radiation shield.

I used the fresh air intake damper. It is normally designed to mount to a 2x4, but I wanted it to be built into a switch panel for a clean look. I bought a special electrical box with a separator for low voltage circuits to keep the damper control separate (Southwire MSBMMT3G). With some holes drilled to make extra space and some modifications to the metal plates, it fit nicely.

I added a switch to cut power to the distribution fan in the attic. I also added an extra wire and switch to interrupt power to the fireplace blower so it could be easily shut off without having to open up the bottom panel. Note that if you do this and you have the distribution fan circuit, you want to wire it in such a way that power is always maintained to the distribution controller, otherwise it forgets its settings with any power cycle. If anyone is interested, I can post a drawing of the modified circuit diagram.

The forced air distribution kit comes with a digital controller. You will need to run at least 4 conductors to it through a thin steel channel. It is very difficult / impossible to fit 2 normal NM cable through this channel, and no wire is provided with the kit. The manual asks for a minimum of 18ga wire. I would purchase some high quality stranded 18ga wire ahead of time so you have it ready for the install.

I purchased the overpriced 25' insulated 6" duct made specifically for the intake kit. It has a higher temp rating, so I felt better about using it connected directly to the fireplace. I found that it was slightly oversized and to get it down nice and tight with hose clamps, it will start to tear. You will want to use duct sealant (I got a 1/2 gallon pale) on all connections. This ensures no leaks, and significantly increases the joint strength.

I did not like the idea of first creating a fire wall between the chase and the attic and then compromising it by punching a hole for the distribution ducting. Not required by code (and usually an industrial thing), but I installed a fire damper with a fusible link which should automatically melt and slam shut in the even of a fire in the chase (Jedco FDCHS1206).

I just used a standard duct connector to go through the code required fire break. A second fire damper would have been better, but there would be no way to access it if I ever had to replace the link.

To support the blower fan I hung it with paracord rather than hard mount it to isolate the noise. In hindsight this may have been overkill, as it is very quiet. Since I was pushing / exceeding the recommended max run (I ended up at a total of 65' of ducting combined), after the blower I switched to an 8" R8 insulated duct to help with back pressure. The 8" duct is technically not rated for the 250F requested by the manual, but the provided fan is only rated for 140F so I doubt it will ever see anything much higher than that. The fan is also only rated for 260cfm, not the 300cfm advertised.... However, upgrading would be easy if desired.

I plan on adding an inline thermometer just after the fan to see the temps before any heat loss in the 50' duct run.

Right now I have it just running to one room (the furthest). Eventually I am planning on running it to 5 rooms with electric dampers in each offshoot; all controlled by a smart home setup to swap which room is getting heat depending on demand.

I wanted to be absolutely sure no water ever got in through the chase cap. However, the ventilated roof flashing created some interesting challenges. I ended up having a local sheet metal shop bend a chase cap for me with a collar .5" larger than the OD of the bottom of the ventilated flashing. Before laying the cap down I used a strip of foam backer rod to hold the steel up near the flashing to slope water away from it.

After using sealant (Geocel 2320) between the collar and the flashing I added a storm collar, so between the slope and the storm collar, the sealant should never even see water.

We can have very high winds. I was concerned about backdraft issues from the wind so I used the Vacu-Stack VSS for the cap. It fit surprisingly loosely and needed to be held up by scrap wood block while adding the high temp silicone. However, after adding the silicone it seems sturdy.

I hope this is better than the typical "homeowner's special" install. Any feedback is welcome.

 

[geofox784]

As mentioned earlier, the ventilated roof flashing cone was, under the right conditions, forming frozen dew on the inside and when it melted, it would form together and drip down. This was not allot of water, maybe a few teaspoons tops, but when it dripped down it hit the sheet metal fire break shield and made a very noticeable dripping sound.

This ventilated roof flashing is required for any 1" thick chimney pipe, and can be avoided with the better insulated 2" pipe. I just didn't have the extra 1" of clearance.

My fix for this was to cut out a storm collar that would go in the ID of the flashing cone at the bottom. (Cut out using a 8.4" inside radius, 9.74 outside radius, 240 degrees around.) This should stops any water that forms before it could drip down. The silicone work wasn't the cleanest given the difficult access now that it was already installed, but I pushed some water up there and confirmed it held.

Drops Forming:

New collar from below:

From above:

 

[geofox784]

A better example of the condensation forming in the ventilated roof flashing cone. This was during exceptionally extreme frost forming conditions, where every tree outside looked like it was covered in snow, but it was in fact all from frost built up the prior night.

In this example, even my collar had some drops of water forming on it. However, it prevented 95% of the water that formed from being able to drip down.

 

[geofox784]

An issue with the forced air fan controller:

The forced air fan controller uses a thermometer that is supposed to be attached to a small bracket holding it off the wall of the fireplace by about an inch. The controller has two temperature setpoints, low fan speed and high fan speed. The lowest setting for low is 95F and high is 120F. I found that it took an extremely long time for the thermometer in it's recommended position to reach 120F, if it even did at all. Consequently, the fan almost never reached high, even though the fireplace was plenty hot to support running the fan on high.

Using a FLIR sensor with the coloring set to > 120F, you can see how the probe has a very low chance of reaching 120F. (This was during a very hot prolonged fire.)

Fixing this was easy. I just removed the supplied bracket and attached the probe directly to the wall. I used it in this configuration for half a season with absolutely no issues. IIRC I ended up increasing the low setpoint to 125F and high to 130F and this seemed to do a good job of only running the fan when the fireplace was hot enough to support it.

 

[geofox784]

I ended up finding that the forced air supply was so powerful / hot (even with a 50' duct run in the attic) that it was overkill for my bedroom. Instead of wiring into the optional shutoff circuit for the fan, I added a thermostat in my bedroom that controlled a relay circuit with two electric dampers. Once the bedroom is warm enough, it automatically closes the bedroom damper and opens a damper that diverts the air to the conditioned basement.

I did find that the dampers closed much faster than they open, so when switching modes, both dampers would briefly be closed at the same time. This would result in the ducting getting inflated and air rushing through the small opening as the damper opens, creating unwanted noise. To fix this, I plan on wiring in a delay circuit.

Dampers - Zonemaster normally closed ZC208

24V AC Relay

Delay - ICM Controls ICM253

To get the air down the basement, I shrunk a closet to create a chase between floors. I also added a 2" conduit pipe later used for running speaker and ethernet wire.

Vent in basement:

 

[geofox784]

And here is the final result!

The mantel is from a reclaimed wood store.

The stone is (broken link removed).

The tile is (broken link removed). I sealed it with STONETECH Enhancer Sealer (important to prevent ash from staining it.)

I plan to swap the plate for the damper controller to a laser cut white plate later.

Total project cost was $16,933 and about 6 months work on my days off. I can't imagine how much it would have been had a hired it all out.