The entire painting process took 4 days. I think I cleaned the bricks the weekend before I began painting. Our entire wall is brick, so I would think yours will take less time. I think I started painting late in the day on a Thursday (primer), finished the primer Friday night, first coat of paint on Saturday, and finished up with the second coat of paint that Sunday. DH and I scrubbed the bricks with a powdered cleaner mixed with water (TSP-PF). The primer (BM First Step, 100% Acrylic; tinted grey), took about a day and a half (maybe a day and three-quarters) to paint--DH helped briefly if I recall. I think I only used a brush, but might have rolled it on as well--I forget. It really soaked in so it was slow going. We did one coat of primer. For the first coat of paint I just used a brush (don't remember if or how much DH helped with painting the first coat). Lots of nooks and crannies, crevices, and mortar lines, lots and lots of mortar lines needed to be filled or covered with paint. The second coat went much faster. DH used a brush first, to paint all the mortar lines, and then I rolled on a decent coating of paint over the bricks using a really, really thick, fluffy roller cover (thanks to the recommendation of a professional painter who saw me eyeing the paint supplies at HD--I don't think that my go-to paint store even had a roller cover that fluffy!). Then of course, there were the touch-ups. Where our side walls meet the bricks, there are gaps all up and down at those junctures. Combine those gaps with the wavy, bumpy brick wall, and you can well imagine how impossible it is to tape the bricks in such a way that no paint gets through. What's the opposite of a clean sharp line? LOL Luckily I'm tenacious (and more than a wee bit detail-oriented!), so I spent whatever time it took to touch it all up using my trusty array of small (and even smaller!) brushes. I think I did one side of the wall/room one day, and the other side the next. FYI, small unpainted holes and spots might mysteriously appear after you've painted the brick (even weeks later)--the paint seems to form a bubble over or around cracks, crevices, and holes and then sucks in as it dries, leaving bare brick, or primer exposed. I went around with a tiny paintbrush, filling-in and covering up all of those spots with the black paint. I touched up all the mysteriously appearing holes/spots, as they appeared (or whenever I noticed them). We used BM primer tinted grey as I mentioned (not as dark as I'd have thought it would be, and I would have liked it darker), BM Aura paint, matte finish, in Black, just plain old BM Black. Love Aura matte! We used Purdy XL angled (and maybe flat, as well) brushes. I don't know the name of the roller cover--might have been a Purdy, but it looked like a thick and fluffy wad of sheep's wool on a roller.

Here ya go Jewel. For comparison, behind it is my Emtek entry door lockset with flat black finish. The paint is covering very cheap shiny gold brass. I should have painted the wood as well, but will go back and do that later. This is 3 coats. Although it's flat black, it has a slight luster. It's not a dead black.

@cat_ky Thank you for the input. Yeah, the room is TERRIBLE when it comes to light. The only window (a glass slider) faces N.E. so, natural light is pretty minimal. I have another thread going regarding how to go about figuring out the best way to get the room some more light. I've explored all the options on my own, but I really think I need to bring in a designer to weigh the various options vs. their costs and then go from there. This room is also open to the kitchen that will need a reface as the very least, so there's certainly plenty of work to do and to figure out to help out this space.

Monica, Not only are there size limitations to custom doors, there are things that make it where standard doors won't fit even if your fireplace is within the size constraints. Brick columns at the opening, a ledge across the top, uneven facing like stone, arched openings are all examples of reasons you would need a custom door. Post some pictures of the fireplace along with the dimensions and I'll tell you whether or not you need a custom door as well as provide some advice on why you may or may not want custom doors based the pictures you provide. Just so you know up front, I sell custom doors...have been doing so for over 30 years. It's no secret here on Houzz. I create mockups to show you how doors look on your fireplace. You can read more here: Free Fireplace Door Design Service at Hansen Wholesale