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Comment by ynac | Hacker News Reader

When we lost power for 10 days a few winters back we attempted to use the fire place for heat. It was a fail. Post and beam house (large wide open floor plan) with a large transfer from 1st to 2nd floor, and apprently my lack of skill for optimizing heat over beauty in the fireplace, left us without much of a thermal bump. To this day I swear we were pulling heat out of the chimney faster than we were heating the house; I cooled the house with fire.

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An open fire is not a particularly warm thing to have unless you’re directly in front of it. Most of the heat goes straight up the flue, and it uses an enormous amount of air to keep burning - it will pull huge volumes from rvertwhere it can. This is why these old buildings didn’t suffer from damp issues - the open fires burning were ventilating them.

It's the same problem as those portable AC units: the exhaust (chimney in this case) draws large amounts of air in from outside which is at the wrong temperature (cold in this case).

At some point they realised and the newer ones have a dupex air duct so you can keep air pressure even

Huh, just like a balanced flue.

If it has a flue or chimney, it isnt really an open fire. Look at an ancient long house, or farmer's thatched cottage from say 400 years ago. They had a fire on a stone circle on the floor in the middle of the room, and a high roof sometimes with a hole but often not. It was smoky, but kept everyone warm.

It gave people lung cancer, too. Maybe genetic adaptation to that (pretty toxic) environment is why smoking doesn't kill people more quickly.

I think before heating without smoke, it was perfectly sensible to smoke tobacco because it was the least bad thing you were inhaling on a daily basis, and you were likely going to die of lung cancer regardless. Makes sense we didn’t really discover the risk until after we stopped using wood burning stoves (or burning coal, like Laura Ingalls Wilder’s mother would to in Little House when it was available)

Sorry, it’s not a topic I know an awful lot about. I was talking about an exposed hearth with a chimney like in the article, as opposed to a cast iron unit that recirculates the air like a stove

There have been times, with various crises, where I only half considered if indoor plumbing was such a great thing. But that's probably a very old-fashioned New England thing.

Yeah, if you actually want to heat the house with fire you’ll want an insert or a wood stove. Otherwise most fireplaces in most houses are decorative, and one pays for that decoration with heat loss.

And even those will require draft from outside the insert / stove, so either you build them with an inlet from outside, you pull cold air from badly sealed doors / windows, or the chimney draft will be insufficient.

They will require breathing but much less than an open fireplace and a lot more of the heat will be kept inside and not sent through the chimney. So overall they’re way on the positive side. If you can get a cold air inlet it’s better, but it’s far from necessary.

By law new wood stoves in many places MUST have an outside air intake

> insert / stove

As a kid I lived in homes with both - and a home with a barrel stove - and as an adult with a pellet stove and I don’t remember that being a problem. Net, it was fine?

That’s not uncommon, but having grown up in a house heated by wood fires I knew that when building our current house. The main fireplace is on a central wall and has enormous thermal mass. Beauty and utility can be combined.

My grandparents' house was this way - the chimney was in the center of the house (built sometime in the late 1800s and rebuilt in the 1950s).

The fireplace had a stone chimney - and the kitchen was built in an 'L' shape around the first floor of the fireplace. The (master) bedroom (an additional bedroom was built in the 1950s), the stone of the chimney was a good quarter of one of the walls.

I do, however, think that the rough hewn stone and mortar of the chimney with the insets around it had a certain rustic beauty... aside from the "that got warm" in the winter and could keep the kitchen, living room, and bedroom warm.

It's pretty much 10 to 20% efficiency for an open chimney and 80% for a good wood stove so your result isn't surprising.

Open floor plans also destroy the efficiency as the heat goes up which made your already inefficient heating even worse.

Combine both together and you probably have 5% efficiency.

A ceiling fan works really well for this

To use it effectively you want one with water jacket and just use that hot water with your normal house heating system. You don't need much power to run circulation pump so UPS + some solar panels should be enough even in deep winter. There are also systems that get it out of the exhaust but that doesn't get you much heat storage, just instant heat and generally less efficient.

Old school version of that were masonry stoves that come with ton+ of mass for the bricks and smoke being routed all over (often including a place to sleep) to take as much heat as possible from it.

If I had money for that I'd put a big hot water tank for buffer, heat it normally with heat pump, and just had emergency water-sheathed fireplate, with big buffer you can just fire it up once and have tank slowly give the heat back to the building. Or fire it up at the coldest days to save some heat pump power in days where there is barely any solar.

This isn't a good idea because the water cools the fire too fast and you tend to get soot build up inside.

I know someone who gets through the winter off their fireplace. Really old timber house with riverrock chimney. Their fireplace looks nothing like what you think of a fire place looking. You can’t see the fire, there is like this big iron door in front of it. They go through a huge pile of wood every winter, along with a couple electric heaters for rooms or office.

I assume most decorative fireplaces on the other hand are not built to heat the house.

There are a bunch of these on our island. The fireplaces are in the middle of the house, small doors, and once they get that brick warm the houses are 80 all winter long. They were built by Russian families in the 1940s, maybe a couple dozen homes on about 300 acres. The rest of the home's construction was typical; except for a few innovative walkways between main house and garage. I'm guessing it's what they knew from their homeland, even though temperatures here rarely drop below 20, and then, only for a short time.

That sounds really interesting. Which island is that?

There's a whole site dedicated to the (highly efficient) Russian/German stove: https://larsenfamily.com/russian_stove/nojava/index.html

I grew up like this. We had special glass plates on the doors so you could see the fire (though this meant cleaning the glass every week).

Yeah fireplaces don’t make sense to me. Hot air rises and it sucks the existing heated air in the house which all flows out. The only way to heat the space is you need something with a lot of thermal mass that heats up in the process and then radiates heat. So a lot of bricks around the fire, some sort of baffle to enable the heat transfer and a system that sucks in air from the outside.

What you imagine is called a rocket stove mass heater, and it has other names too. Works wonderfully well.

We saw stoves/fireplaces like this in a bunch of taverns in Slovenia. Huge hulking tiled cubes around the center of the building that just radiated a pleasant heat from every square inch of the surface. I imagine it was quite efficient, with just a very low fire burning to keep it in equilibrium.

If it was a rocket stove, it was a very small very hot fire. I've had a bit of a love affair with rocket stoves lately (even replaced my BBQ/grill with one).

I like the idea of an outside vent, and unfortunately, I think an insert of some kind. I can't help but first think of the goofy look of a wood fired stove sitting half in and half out of the fireplace. Surrounded by a few tons of river rock. That said, after a couple days of a couple degrees, it's either that or the tent in the basement.

*outside intake. The vent would just be the chimney.

The problem with outside vents is sometimes smoke goes out them - air comes down the chimney.

It's challenging to design the exhaust so that the smoke goes away, but not too much heat.

Did you use a fire grate with a big space underneath and keep it swept clean? Or did you build up a big bed of ash under the grate? On the advice of a chimney sweep I put a perimeter of bricks under the grate to form walls and we're currently filling it with more and more ash (it really takes a while). It's starting to make a difference in how much heat comes back into the room. Without that void underneath, the fire doesn't burn so hot and cold air doesn't get pulled through so quickly.

(It feels like it's getting warmer - may all be wishful thinking though, I haven't taken any measurements!)

the fresh air inlet should be piped along the chimney walls, this would also recover the condensation heat of the water produced during combustion, but its not trivial to design while keeping in mind things like maintenance, different chimney column temperature (and thus different convective forces), capturing and effluence of the condensed water, ... the heated fresh air should not directly go to the fire but piped into the room.

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