The Secret to a Warm Fireplace

~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 after all), 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.

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The Count

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’.

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If U.S. fireplaces were a pickup truck

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 pretty, 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.

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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.

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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 logs 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.

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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 conversion we did, from a conventional fireplace to this beautiful Rumford (and it doesn't hurt that the client made fantastic design selections with these gorgeous, custom stone legs and mantel).

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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:

• Hooray! After many sideways glances from family members, that fire is going. And it looks great, and you’ve thrown on enough wood to make a beaver blush. It even heats you up some, if you stand exactly. directly. in front of it. You’re proud. We’re all proud. So one, maybe two people stand and feel the heat while the rest of us look at their behinds.
  
  
• Hours have passed and you’re ready to be done now, but there’s a huge pile of super hot embers, and loads of ash, from so much wood. So we can’t close that damper now...it’s gonna take hours for it to cool down enough to be safe...we’ll close it in the morning. In the meantime it sucks the heat out of your home while it completely stops putting out its own heat, and then of course you do forget to close that damper in the morning. You’re reminded of this days later as you find yourself chasing a beautiful but uncharacteristically dirty duck around the living room with a blanket.
  
  
• For some of us, this is a perpetually smoky experience, as the draw is never quite right, swirling smoke into the room, and is often accompanied by dangerous, repeated creosote buildup. You’re reminded of how it felt 25 years ago in the bars.
  
  
• Some of us try putting doors on there. So the heat we feel is reduced considerably, and we sure don’t get that primal fire feeling - it’s a little ‘tidy’ now, isn’t it - but there are at least a few possible or perceived advantages: less fear of sparks flying, or potentially less heat loss up the flue due to choking the source of air somewhat, and particularly if your chimney is on an outside wall, doors could indirectly help reduce smokiness in the room due to temperature differentials...long story. But in my opinion, maybe now we might as well have gas logs, and at least we’d get some heat out of it.

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:

• For starters, this could be a brand new fireplace/chimney that you’ve hired us to build, in a new home, addition, or remodel...OR, it could absolutely be a retrofit, changing out an old unit. Annnd...as we are masons (i.e., “ar-TEESTs”) after all, while we’re making your old fireplace more functional, we might as well rip down that nasty old 70’s fakey stone that’s on there, and put up some beautiful new stone, or brick. We’ve changed fireplace faces from funky to formal and vise versa, and we’ve reduced huge walls of stone or brick to simple surrounds...lots of options here. Instead of your dated fireplace creating spousal division, let’s all hold hands and feel the love with some fresh stone we can all agree upon.
  
  
• In the course of building this new firebox, we now in many cases remove the old bottom damper and smoke shelf entirely. At the top of the chimney (outside), we install a spring loaded, top mounted damper. This is controlled via a cable into the fireplace area. When you close it, unlike bottom dampers, it actually seals decently well, which helps to keep your heat bills down, critters out, and downdraft from giving you that charming smokehouse smell in the home when you’re not burning a fire (NOTE: I’m again talking about strictly wood here; life changes if you have a gas line installed...you’ve gotta leave your damper open in those cases, a safety thing).
  
  
• This design has important functional changes. Rumford believed strongly in having a simple and unimpeded way for smoke to exit. Traditional smoke shelves force the smoke to change directions, and can create swirling and other effects that conspire to mix air in ways that interfere with draw and allowing the smoke to leave cleanly. Our Rumfords utilize a smooth, curved ‘breast’, and generally a straight back, that the smoke easily follows up and out.
  
  
• Traditional fireboxes are wide, deep, and not usually very tall, and you mostly lay a bunch of logs in a pile on a big metal grate. You’ve got a ton of wood, way back in there, and almost no heat is reflected back into the room. You feel a little from direct exposure to fire, and the rest bangs around in the box and literally heads straight up the flue. By contrast, Rumford fireboxes are generally taller than they are wide, or at least close to square. They’re shallower, and don’t need to be deep. The angled walls, left and right, provide significantly more reflectance of radiant heat, and a MUCH wider ‘field’ within which to feel heat; you can be off axis and no longer have to be standing exactly in front of it to feel it. This all does a considerably better job of reflecting radiant heat out into the room and the occupants...this firebox design is really the ‘a-ha’ thing about Rumfords in making people feel warm.
  
  
• Part of the original idea of Rumford was to be able to use fewer logs, and still produce heat. With a Rumford, you ideally (but not necessarily) stand them against the back wall, vertically. Having them arranged like this increases the amount of flame, while using fewer logs. Really beautiful, lots of flame, easy to manage, and not nearly as much ember and ash as a big old pile. You’ve just gotta make sure you have adequately dried/cured firewood.

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.

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