~by Karl Zarling
AHHH, FIREPLACES - Gosh, how we love them. If only they worked better. This is the story of a fella known as Count Rumford, who was presumably at some point...cold. Sometime in the late 1700’s, which feels like a cold time to me. He believed fireplaces could work better, and he decided to do something about it. Most of us in the U.S. never got the memo describing how to make a natural, wood burning fireplace that works well, but luckily for you, here at DAM we did get that memo, and we’d like to tell you a little about it. You want to know the secret to building a toasty and efficient fireplace? Read on, chilly friends.
Quick ground rules - before any of you get all worked up and ALL CAPSY AND RUN ON SENTENCEY (this is the Internet and I’ve heard of such things), let’s make a few things clear: I am not here to debate the economic virtue or efficiency merits of an open, natural fireplace versus something like a modern, efficient woodstove, or an insert, or gas burner, or pellet stove, or how dumb I am and how much smarter any of those things are. If you’re thinking about going there, let’s just agree that a high-efficiency gas furnace beats all of those options, if we’re purely talking heating efficiency. Note that I am not including masonry heaters in that mix as they are a whole different animal, and shall be covered on another day. The point is that there are many here among us - including myself - that just like fireplaces, natural wood burners, with no doors in the way, or blowers, or any other mechanical magic. The fire is magic enough. And we believe there’s a better way to build fireplaces. Are we good here? Excellent. Moving on.
Per Wikipedia - so it must be true - this Count Rumford fella was actually born Benjamin Thompson, in Woburn, Massachusetts. He’s regarded as a physicist (though barbers kinda were, too), and a scientist, and inventor, among other things. Props: he’s got a moon crater named after him. Now, he didn’t necessarily get everything right, and there were assertions he’d made that were proven to be incorrect. Mostly it seems like Thompson/Rumford liked to turn conventional beliefs upside down and explore possibilities that others had dismissed or were just not curious enough to care about. For this he ranks high on my Informal List of Dudes, and deserves to be called Count Something, anyway. And some of what he did get right had to do with heat. We’re going to focus on Rumford’s fireplace observations, beliefs, and designs, and from here forward I’ll refer to this general kind of fireplace design as a ‘Rumford’.
HOW IT’S USUALLY DONE - Here’s a mental picture of how modern or conventional (NOT Rumford) fireplaces are mostly built in the U.S. They generally begin with an overly big, deep firebox - the part you place the wood in, where it actually burns. Unlike a lot of timber-light regions of Europe back in the day, the U.S. has largely enjoyed a relative abundance of burnable wood, so by goodness we like our fires big, which means a huge firebox. Which as an aside can look awfully silly when we don’t have a massive fire burning...so we’re really just wasting wood now, but more on this later. Then this thing called a smoke shelf is built above the firebox, typically along with a bottom mounted damper.
These modern fireplaces often don’t draw very well, and usually don’t heat well, either. Sure, they look purdy, and hopefully smell good, and that’s great. Again, if we were after purely heating efficiency or safety we most certainly wouldn’t cut a hole in our roofs and build a fire right there in the middle of our living room, nevermind all the problems this intentional hole in our roofs can cause (again, another discussion). Nonetheless, we can still try and do better at these, right? As I said, I love fire, and fireplaces. There’s something primal about fire; it’s mesmerizing, satisfying, calming, sexy, the whole deal. The fireplace, the surround, and chimney all add aesthetic interest and appeal to a home, and they can absolutely improve a home’s salability.
THE RUMFORD WAY - So how’s a Rumford better? Here are a few big pluses: 1) a smooth ‘throat’, designed to improve draw up the chimney, 2) angled side/back walls, which provide more reflection of radiant heat, directing it out toward people and the room, and 3) overall more warmth using fewer burning logs, while still producing lots of beautiful flame.
THE THROAT - The smooth throat is nothing like the ‘smoke shelf’ approach. Rumford’s feeling was that the best way to get smoke moving up and out of the stack was to remove anything in the path that would impede it. Imagine turning a miniature fireplace upside down...and pouring water into it. Water flows cleanly through a smooth path. This is how Rumford designed his fireboxes, allowing smoke to smoothly exit vertically. The myth is that you just need to make the firebox deeper, to somehow make the smoke ‘stay in the back’ and go up the flue (and not into the room). It just doesn’t work that way. Part of the problem is the hoops the smoke has to jump through to actually get up and get out of there, and the way it swirls and mixes along the way.
*Note that how a chimney ‘draws’ - how well/easily smoke rises and gets out the stack - also has everything to do with building pressurization and ‘make up air’. Suffice it to say that modern, tight houses can present challenges to fireplace draw, as do other factors, if the stack is on an outside wall, or centrally located in a home, relative chimney height, lots of variables...which we’ll also have to cover in another article!
**One more, related to the throat and lack of a smoke shelf, a quick note on dampers. When we are building a strictly wood burning fireplace/chimney, with no gas appliances in the firebox or even gas assist to light a fire, we generally recommend and install top mounted dampers. These are better sealing and therefore more energy efficient, and they do a better job of keeping critters and weather out of the chimney flue. However, when we have any gas lines running to a firebox, we recommend bottom mounted dampers. Building code requires that fireboxes that use gas lines have dampers that ALWAYS stay open at least slightly, to allow potential gas buildup to escape, and this is the easiest/safest way to ensure this.
THE WALLS - Here’s the biggie, what I consider the real difference maker in Rumford design. So in modern fireboxes you’ve got this deep configuration, a horizontal box, with an iron grate at the bottom to hold a big pile of logs.
What happens here, unfortunately, is nearly all of the heat from the fire goes right up the stack, and not into the room.
Rumford fireplaces generally are more vertical...taller and sometimes narrower. They have a much narrower back wall, as the side walls are turned in at the rear to give them much more of an angle relative to the front.
It’s this angle and the reflection produced that delivers radiant heat to you in front of the fireplace. I will vouch for this...these things throw off a remarkable amount of heat as compared to a traditional firebox. And the entire firebox is generally fairly shallow, which further helps bring the heat into the room and not up the chimney.
FEWER LOGS - MORE HEAT - Also note that while you don’t have to do it this way, the intention with Rumford is to simply lean the logs on one another vertically, against the back wall. Some of our clients still like the look of iron grates, but these are really not necessary, and yes, you may stack them horizontally, just like Dad always did it. But because the unit is more vertical in design to accommodate the logs in this way, more actual ‘flame’ is produced using fewer logs, producing more heat and eye candy while using less fuel (wood)!
Fun fact: if we're really doing this right, we actually light this wood at the top. I know, the humanity, right? Seriously, google it. It burns cleaner and more fully, less ash, all good.
OLD SCHOOL BEAUTY - These fireboxes are also really pretty, by the way...they’re not like a standard dark, sooty thing that looks terrible unless it’s burning. We have color options for the fire brick itself, and our masons are able to do different patterns, herringbone looks, and even combine multiple brick colors to your specification.
Here's a photo of a small conversion we did, going from an ordinary fireplace - that almost never got used, as it wasted more heat than it created - to this pretty, efficient Rumford, that sees a whole lot of burning action these days. And for a small fireplace, it really throws some heat.
THE BULLET LISTS - Let’s take a moment to reflect upon and review a few Common Fireplace Bummers (CFBs), virtually ALL of which I’ve personally experienced, that are commonly solved by using a Rumford design:
IT GETS BETTER - Of course there’s more, but let’s clear our palettes of this Bummerplace (see what I did there) and hit the high notes of how life could be improved with a Rumford:
IN CLOSING - I hope this has been a helpful addition to your ‘all about fireplaces’ knowledge, and maybe it’s opened your eyes to the benefits of this terrific design, one that really only a small percentage of masons have much experience with. Dale Anderson Masonry has been learning and applying new and improved techniques to their work for decades, and in this case, it took a look in the rear view mirror to find a great solution for the future. Thanks for reading along, and as always, feel free to contact us to chat about your next masonry project.