I've had a similar set up on a sealed fireplace for 20 years - no issues.

To me - that looks like it's gentle, and the diameter is large enough to not be an issue.

Thanks. I think sealed would be quite different from open wood burning?

A 30 degree from vertical bend in an insulated metal chimney is a standard detail and will not cause the chimney to overheat or alter the performance of the fireplace. Usually, a residential chimney is limited to 2 separate offsets. and If the angled portion is longer than 8 ft,, it should be supported at the middle. Make sure no combustible materials are within 2 inches of the chimney pipe.

Building codes require that manufactured chimneys be UL tested and the installation requirements shown in the installation instructions. If you are curious about good installation practice, just google the chimney manufacturer and model number.

Thanks. I think sealed would be quite different from open wood burning?

I think that airflow is airflow...

I am not a chimney guy, but the fire box of the fireplace isn't centered. Aesthetically once this is enclosed it won't look that appealing.

Real Estate value is widely determined by homes that look appealing, you know so you don't wind up taking pennies on the dollar having to sell to the 'ugly' home people when the time to sell it comes.

So because the firebox is not centered... the mantle if installed will not be centered. It will look odd after all said and done.

Most homes are mortgaged for 30 years. So if you keep the home for that long... you'll be paying for 'looking at' a fire place that looks crooked.

The mantle should be 'centered' over the fireplace opening. For those reasons I wouldn't go for this. I wouldn't want to look at something 'crooked' for 30 years...

But that's me.

"I am not a chimney guy, but the fire box of the fireplace isn't centered. Aesthetically once this is enclosed it won't look that appealing."

This is actually fairly common. Should be OK once finished: :-)

Read the manufacturer's specs and/or ask the contractor and/or supplier. That's what I do if necessary, but then I use a well trained & experienced installer/supplier I've known for a few decades.

"I think that airflow is airflow..."

Perhaps. A sealed fireplace is typically a closed system, has fairly low air volume and often has a blower in the flue. The minimal heated air generated has nowhere else to go but up the flue.

A wood burning fireplace needs to draw well to both keep the fire supplied w/ sufficient oxygen and to insure that smoke goes up the flue rather than in to the room.

"Read the manufacturer's specs and/or ask the contractor and/or supplier. That's what I do if necessary, but then I use a well trained & experienced installer/supplier I've known for a few decades."

Thanks. Yep, done that. I think it's often important to go beyond that though. Manufacturers and dealers are incented to sell stuff. They want their product to fit in as many diverse situations as possible so long as it will perform to some minimal spec. Users and others who are not incented by sales might have better information about how it will actually perform.

"Building codes require that manufactured chimneys be UL tested and the installation requirements shown in the installation instructions. If you are curious about good installation practice, just google the chimney manufacturer and model number."

Building codes and UL are minimums. They do not insure high quality and often don't even insure that something will work.

HRVs/ERVs installed to typical building codes and according to UL approval where the fresh air is injected in to the return duct often do not even accomplish the 1000ppm CO2 that ASHRAE says should be attained, much less the 600ppm that the medical community is recommending.

Or a simpler example, the minimum floor joists allowed by code and that building inspectors will approve result in a quite bouncy floor. Better to build better than code and have a solid floor with no rattling furniture every time you walk through a room.

"It seems like the full heat of the exhaust is going to be hitting that one part of the flue pipe right where the turn begins, the segment that's above the short vertical piece exiting the fireplace. Does that matter, is that a risk? I don't know."

Exactly my concern. It has no chance to establish any natural velocity. It's possible that once it gets going that it will draw well enough in the vertical segment beyond this and create enough of a vacuum that the bend isn't an issue. Like you, I don't know.

Opaone if you look in the firebox up to where the exhaust goes, you may likely see a baffle or plate. In other words, the flames and heat likely aren't going straight up. Both a safety and heat/efficiency thing I understand.

Story time:

A friend of mine, who was a partner with one of Frank Lloyd Wright's apprentices, told me of a time when he was given a tour of Taliesin West by Wes Peters. In one of the apprentice's quarters, my friend stuck his head into one of the fireplaces and looked up the flue, he saw sky. He asked Wes about it and he replied, "We were learning a lot back then."

Optimal is without bends. That might require a change in the relationship between the interior of the fireplace and the exterior flue as it looks like the offset is to create a centered exterior exit.

I rely on my long term venders to give me excellent advice and fair pricing. Sometimes I pay a little more, but loose less sleep, and deal with fewer idiots.

An enclosed fireplace is a gas-fired, direct-vent system with a double-walled chimney. Hot gasses rise in the inner pipe and fresh air is drawn down in the space between the pipes. The temperature of the gasses is far less than with a wood burning fireplace.

Your open fireplace is wood-burning and has a double -walled chimney with fire-proof insulation between the pipes.

Your fireplace will not have a traditional smoke shelf and damper that can reduce the draft so you should have a strong draft regardless of chimney offsets. A chain operated damper should be at the top of the chimney and fresh air should be ducted to the firebox.

"Building codes and UL are minimums. They do not insure high quality and often don't even insure that something will work."

Its ridiculous to compare the rigorous efforts of UL, ASTM and NFPA to protect the public from the loss of life and property from fire to building code lumber span tables.

Instead of guessing or asking for advice from strangers about factory-built chimneys, go to NFPA's website and download the free version of NFPA 211 and read chapter 6.

"you should have a strong draft regardless of chimney offsets."

Not exactly. Anything that interrupts upward flow, a bend or jog, sections not perfectly vertical, dampers, will all create increase static pressure and reduce draft. The question is how much and to what impact.

One of the most important things to create proper draft is the temperature of the chimney all the way up and out of your house.

If the chimney is an exterior rise it can be colder than the high interior spaces of the house, and the Loft Effect will pull the smoke/ exhaust into your room.

"Opaone if you look in the firebox up to where the exhaust goes, you may likely see a baffle or plate. In other words, the flames and heat likely aren't going straight up. Both a safety and heat/efficiency thing I understand."

Yes. Typically after this though the chimney rises straight up from the smoke chamber (the area behind and on top of the damper) which creates draft or IOW it creates low pressure in the smoke chamber and so pulls air from the firebox through the throat & damper. to send it up the chimney. This 30° offset section reduces draft and so reduces the low pressure and so how much vacuum there is to pull air from the firebox. Enough to cause a problem?

"Your fireplace will not have a traditional smoke shelf and damper that can reduce the draft so"

Oops, I goofed when I pasted this above.

Why would you say this about a wood burning fireplace? The damper and smoke shelf/box are, to my limited understanding, critical to proper functioning.

"Its ridiculous to compare the rigorous efforts of UL, ASTM and NFPA to protect the public from the loss of life and property from fire to building code lumber span tables."

Not really. Those organizations are focused on safety issues, which is critical. They only look at performance or quality functioning where it impacts safety. With a fireplace they are going to make sure that it basically functions and does not create a safety issue. If other than that it is poorly designed or allows for installation that results in poor draft and poor performance they don't really care - that's a consumer issue.

Similarly, the calculations for floor trusses are to insure basic stability - the floor won't collapse under normal use. This does not guarantee a very solid non-bouncy floor. For that you have to design the floor system to a higher standard than code minimum.

Another example is HRV/ERV installation in the U.S. where it is allowed by code, and very often done due to costs, to pull stale exhaust air from the return duct and then to push fresh air in to the return duct several feet downstream. It has been known for some time that this frequently does not result in fresh enough air in bedrooms at night and recent studies are proving this to be true.

Relying on building codes, industry standards or safety approvals for quality construction or quality functioning is an ignorant and unwise choice. These are all good and I'm glad we have them but they are minimums - the worst that you can get away with by law.

No idea.

Build a fire and try it out. It will be fine.