I'm going to assume you read the installation instructions for the gas fireplace unit and built the fireplace according to those instructions. If done properly, you shouldn't be having this problem.

Are you DIY'ing this? If so, I might stop and get a fireplace specialist out there to make sure you've done the installation correctly before you add the finishing touches.

Definitely not a DIY project. The insert was professionally installed and we're within the temperature rage outlined in the Valor G4 manual.

Experienced professionals who we trust did all the work. I'm just putting it out there in the universe to see if someone has advice or suggestions that we haven't considered yet....

But was there an existing fireplace or is the fireplace a new build?

Existing brick functioning wood burning fireplace.

You said how to reduce the heat to the surface above...this is what I did. This hollow metal mantle will not let the heat rise above it. Gets very hot below, totally cool ontop... I can have candles on the mantle and they don't melt. I have a TV mounted there which is why I researched it so much. But yes, this is a very different style than your wooden one.

I read over the G4 install instructions :

Be aware of hot wall surfaces!

The wall directly above the fireplace can get very hot when the fireplace heats. Although safe, it may reach temperatures in ex- cess of 200oF (93°C) depending on choice of optional accessories. Do not touch!

• Be aware of hot shelf/hearth/floor surfaces! Any projections directly around the fireplace can get very hot when the fireplace heats. Although safe, they may reach temperatures in excess of 200oF (93°C) depend- ing on their elevation. Be careful of touching these! Do not put objects on the hearth or shelf. Temperature of projection surfaces will be reduced when barrier screens are installed.
• Some parts of the fireplace are extremely hot, particu- larly the glass window. Use the barrier screen provid- ed or a gate to reduce the risk of severe burns. The glass windows can exceed 500°F at full capacity.

I suggest you read page 4 for the safety concerns. Nothing should be within 3 feet of this unit!

You have the glass barrier on there, yes? (hard to see in the photo)

The glass front assembly must be in place and sealed before the unit can be placed into safe operation.

Venting ok?

This gas fireplace and vent assembly must be vented directly to the outside and must never be attached to a chimney serving a separate solid fuel burning ap- pliance. Each gas appliance must use a separate vent system. Common vent systems are prohibited.

Finishing Materials

Combustible Materials: Materials made of or surfaced with wood, compressed paper, plant fibers, plastics, or other material that can ignite and burn, whether flame proofed or not, or plastered or unplastered.

What kind of plaster did you use? you would need to check w/that company to see if there is a heat restriction. if there is, you may have to remove and instead float the surface w/a cement or stucco material that is more resistant to heat.

Materials that are reported as passing ASTM E 136, Standard Test Method for Behavior of Materials in a Vertical Tube Furnace at 750 °C.

WARNING

Some materials or items, although safe, may discolor, shrink, warp, crack, peel, and so on because of the heat produced by the fireplace. Avoid placing candles, paintings, photos, and other items sensitive to heat around the fireplace

Installation Planning

Before Installation

1. YOU NEED TO KNOW FROM THE HOMEOWNER:
   Whether any facing material will be used over
   the existing fireplace.
2. What trim, front, and optional accessories (if
   any) will be installed with this unit.

This is not a DIY thing, so I'm glad you had a pro. If you want to read over the specs,

https://www.valorfireplaces.com/media/G4/english/785YN-P-Installation.pdf

Just insure that everything was done correctly.

Other than that, I think the plaster you've applied doesn't meant the heat specs. Best to remove and do something else. Over CEMENT BOARD with nothing combustible behind it.

You can investigate this further, but I think they have a heat resistant plaster/stucco for fireplaces and such.

https://www.plasterersnews.com/heat-resistant-plaster/

Thanks Beth! i appreciate the time you spent reaearching

I'd totally re think the plaster concept to ONLY above the mantel, which I will hope is a faux designed for this purpose.

I'd do a SOAP STONE surround, with the correct substrate, all three sides, and the hearth top below a heat proof mantel. Mendota makes them, if that isn't what you have now.

Soapstone is IMPERVIOUS to heat.

I see "TV designers" putting in these gas flat fronts all the time and I hope there are not children around. The glass as well is super hot! IMPO a gas fireplace is counter indicated when there are children in the home. The sleek look is very modern but it is a HUGE safety hazzard. I see you have a hearth that will keep anyone from just stepping up to it...

@arcy_gw My glass flat front unit has a screen insert that is placed in front of the glass as a safety feature to restrict the ability to touch the glass. It's not really visible IRL, but I imagine the intensity of the fire would not photograph as well with it on. Hopefully the insert is placed on the fireplace after the photoshoot, especially since it's required by the manufacturer. At least mine was.

Just add a fireplace hood:

Let me know if you want one.

WOW not ever going to go with that one for clients no matter what.

@Patricia Colwell Consulting

RE: " WOW not ever going to go with that one for clients no matter what. "

A hood is a viable solution that deserves consideration. Most gas fireplace manufacturers offer them as an option to reduce heat above the fireplace. They can also be custom made in a variety of styles and finishes to suit the application.

As the consummate authority on interior design, can you please expand on your comment so we can benefit from your professional expertise?

Hansen, the point is that adding a fireplace hood is not going to keep the plaster from cracking. all it's going to do is heat up that metal hood hot enough to fry an egg, which would be another safety hazard. Read up eariler on the specs that I posted.

the issue right now is the plaster. Wacky Tacky has a very good point.

but after that is addressed, and IF the hood is a viable option to reducing heat in THIS scenario, then perhaps it could be addressed.

The temporary hood is a fantastic suggestion! Thank you all for taking the time to think about the problem and brainstorm potential solutions

good point Hansen. I hope it works! I was just going off the specs of the Valor install manual. If the hood is an option, and works, great!

According to building codes the material surround a fireplace has to be non-combustible. Was the fireplace inspected by your local building code official during or after installation?

@sushipup2 I'm not sure why you would say I'm spamming. I offered an accurate answer and provided a resource for a unique item I personally designed to overcome the issue presented in this thread. I challenge you to find mention of an insulated fireplace hood anywhere online.

FYI: I am also the one who provided the original posts for @Hansen Wholesale over 2 years ago in this thread. Hansen Wholesale is no longer in business and I now own my own company Fireplace Treatments.

Please don't link to your business website, you can contact Houzz for advertising. Feel free to post good info without the link.

I am not aware of any restrictions Houzz has in their terms and conditions that suggests linking to a business website in a comment is not allowed or frowned upon. Quite the contrary. Houzz provides the ability to add links in comments, which encourages professionals like me to engage the platform, which is a win-win for the OP and professionals.

Would you prefer I posted links to a competitor's website?

Posts like the one from @Alex Jones (in this thread) that link to something completely off topic would be considered spam. I'm not sure why you overlooked that.

If I am wrong about this, please show me where the Houzz policy says I should not link to my business and I will be happy to stop using Houzz.