Open fireplaces suck a huge amount of air from the room. It was once explained to me that in one particular case (a specific house) the open fireplace would typically suck 150 cubic meters of air every hour, when that was replaced with a wood stove it went down to 15 cubic meters/hour. So, an order of magnitude of difference. Those numbers shouldn't be taken as accurate of course, but at least that house got much warmer simply because they didn't have all that air sucked in from outside all winter.
Open fireplaces are inefficient heaters, the house probably lost more cool air due to the fireplace sucking in unconditioned air from outside than from direct heat from the fireplace.
It takes very, very specific conditions (you'd have to go out of your way to minimize radiant heat transfer) for a fireplace to put less heat into a room than it removes with airflow.
Back in the day (i.e. 1700s) everyone heated with fireplaces. And many of them (e.g. 2nd floor ones) weren't that big.
> buildings were taking in 100% outside air to heat/cool
This hasn't been true since fireplaces stopped being used for heating. Even very basic furnaces, such as the coal-fired one my grandparents had in the 1940s, recirculated the air inside the house. (It was an unforced / gravity "octopus furnace", fired with soft coal, with the house temperature controlled via a damper on the chimney.) But it took its combustion air from inside, and was vented via a chimney to the outside, so the house was constantly at a very small negative pressure, and combined with the natural draftiness of prewar construction there was naturally some fresh air intake. But certainly not 100%!
I think it's the newer high-efficiency furnaces where you start to have very high recirculation ratios and consequent CO2 issues. Because they pull combustion air from outside, there's no incidental exhausting of interior air to outside (which would tend to pull in outside air through gaps in the building envelope). Great for efficiency, though.
Fireplaces typically draw air from the house to sustain the fire, then up the chimney or out a vent. That creates negative pressure, which draws cold, unconditioned air from outside into the house from wherever air can leak in.
How this works out in terms of net heat gained/lost will depend on the fireplace design, but, from what I hear, it's not uncommon for this to be a net-loss type of situation.
My vague understanding is that the draft also helps -- the fire pulls the (hot) air out through the chimney, and fresh air gets pulled into the house to replace it. The house may not be any cooler than the outside, but it at least isn't (much) hotter.
I remember those shitty fans from my days living in an apartment. They just shot the air back out into the house. Yeah... those suck. Totally agree!
I think the open concept layouts of many homes in the US aren't great for pungent cooking. The house also has a circulating air system, so every thing you cook goes into every room and closet.
The stove in my rental house has an exhaust hood, and it vents outside. Any idea what a proper cubic feet per minute rating I should look for?
Not all indoor fireplaces are ventilated in the US, actually. (Source: have one unventilated fireplace that is probably mostly for aesthetics and not to be used for extended perios of time)
I live in Pennsylvania and have a Fireplace Xtrordinaire fireplace that came with this house and similar to this. It sucks in air from outside, which is routed around the firebox and heated before being forced into the room. It's called a positive pressure fireplace and it really does heat the 2500 square ft house well. Another cool technology with this fireplace is the catalytic combuster, which allows for almost complete combustion by burning off anything left in the smoke after reaching a certain temp.
I sometimes wonder though, is better to have a negative pressure living space pulling dry, cool air into the house rather than positive pressure, forcing warm, moist air through any and all crevices throughout the house. I guess time will tell..
Most cities here require low or ultra low emission burners, which burn at high temperature, so often the temperature is kept low.
And you are absolutely correct about venting heat. I have not to my knowledge seen a home here with an externally ducted air source. So the room is heated, and heat (warm air) is sucked out of the rest of the house.
Wood is cheap here, and so people often believe it is more efficient jot counting the inefficiencies of wood.
What do you do for fresh air? We have a very well insulated cabin heated by fire, but find the CO2 builds up, particularly overnight with no doors opening, and if we aren’t very quick to close the fire once it gets going, PM2.5 can jump quickly.
Modern furnaces take in outside air for combustion. Using up inside, warm air for combustion is doubly inefficient since you expel exhaust air you already sunk energy into and you are sucking cold air that has to be heated from a much lower temperature.
Modern code for cold climate houses is to be air sealed. A heat exchanger draws in fresh air, raises the temperature with existing heat and then expels cold, stale air outside. Very efficient.
When air sealing was new many buildings developed longevity issues like mold since any moisture issues couldn't dry. All those problems have been worked out and there are homes in extreme cold climates that don't need any energy from the grid they are so efficient.
Having two exits at your disposal works wonders in case of a fire and an open window helps to make sure there is sufficient fresh air in case that heater doesn't work properly. Thanks for the CO / CO2 correction, too much time spent reading up on car pollution recently.
I lived in a 3x2.5 meter room one time. There are obvious drawbacks but it had a surprising amount of advantages too. Using all available space leaves very little air to heat. Where would you get oxygen in a normal house? It's not like my heater can keep up if I open the windows.
Something must be off with your math. I’ve tested opening a window a crack in my building in montreal. The co2 gets low even with two people present. Heating costs did not double.
Anecdotal, but: I have found opening windows to be very effective at reducing C02 (as measured with a good sensor) and not very effective at changing the temperature even when it is significantly colder outside than inside. I live in a single family detached house, so I'm not just getting someone elses heat through the walls.
My suspicion is that this has to do with the thermal mass of air versus the thermal mass of the rest of the house - bringing in ~10,000 cubic feet of fresh air with a fan doesnt take long and dramatically improves indoor air quality but doesnt change the temperature much.
The ones on the outside can use outside air to go up the chimney, avoiding the problem listed above. Harder to do with inside chimneys.
Last place I rented with a fireplace, there was a metal door in brickwork below it in the basement. It wasn’t until after I moved out that I realized what it was for.
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