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Comment by dwohnitmok | Hacker News Reader

> My experience with fireplaces is that the house winds up net-colder

Why is that?

EDIT: Oh are you saying that the rate of heating provided by the fire is less than the overall rate of heat leaving the entire house?

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Right, if you think about it almost all of the heat from the fire goes right up the chimney. The brick of the firebox & chimney are generally built outside the building envelope for safety reasons, so any heat in the brick doesn't warm the house. The only heat that actually makes its way into the house is the radiant heat cast from the fire itself, which is small.

The smoke is poison, and unlike a furnace, gas fireplace, firebox, or wood stove, there is no heat exchanger, so you can't capture any of the heat out of the flue gasses.

It's counter-intuitive, I know. But this is why everybody congregated around the hearth in the days of fireplaces.

Ah the only heat exchange being radiant makes total sense. Thanks!

Why don't we run radiator water pipes across the chimney, to bring that heat back to the house?

There are designs that do this or things like it. In the US, though, it seems fireplaces are mostly an aesthetic feature and not a practical one.

This is a very old problem and there are solutions, like the Franklin stove [1]. However, we don’t really use fireplaces as a primary source of heat anymore. Their use is really more decorative. If they were really intended for heat generation, so one of the other posts mentioned, we would use a completely different design.

[1] https://en.m.wikipedia.org/wiki/Franklin_stove

My father did that a long time ago in a house that had baseboard heat. Made a fire grate out of plumbing pipe, ran the baseboard water through that. It worked, when it did. It would also somehow get air in the lines and start banging from time-to-time. I was a kid, so I don't know if the monetary savings offset the pain in the arse, or not.

In parts of Europe (definitely Germany) heating with water based radiators throughout the house is normal. And that goes from individual houses to big apartment complexes (I lived in a 52 unit one with a central furnace). It's totally normal to let the air out of your radiator from time to time. And they (or you in the individual house case) fill up the water in the 'closed' system from time to time.

Different places, different 'customs' i.e. systems we are used to. All have their pros and cons and sometimes it's just that we don't know that different systems exist.

Radiative heat actually makes you feel significantly warmer, so you can set your heating to a lower temperature and still feel the same warmth compared to airflow heating. This is the reason why floor heating is very efficient, because you have a large heat mass with radiative heat that sits at your feet (which typically get cold first). So it provides the same comfortlevel at significantly lower temperature.

Which is why it is better to make a quick but strong draft in your home than keep window constantly slightly open. With a quick exchange of air, your walls remain warm and continue to radiate heat. Having a window constantly slightly open means air exchange is slow but constant and the area of the wall around the window cools down significantly.

Same in France. There's variations in how the water's heated (gas, fuel oil, electricity) but it's the default form of heating everywhere.

Wood boilers are common enough. Pipes and radiators won't do all that much good if you aren't moving the water, and at that point it makes sense to optimize the whole thing for heating water with the minimum required fuel.

The house I grew up in in Scotland did exactly this.

We had fireplace powered central heating -— radiators throughout the house linked to pipes behind the firebox. In the morning I’d wake up to ice on the inside of the windows, and by my teenage years it was my job to head downstairs and light the coal fire first thing in the morning. It worked well once the fire was up and running.

This was in the ‘90s btw, I’m not _that_ old.

This is why russian-style stoves have a whole labyrinth for the air to blow through, warming up the large brick structure. It can hold heat for a while even after it's done burning.

A bit OT, but I would have no idea about Russian-style stoves until I saw this video a few days ago. Amazing.

https://youtu.be/r_TO30jzyUA

The 180 year old house I grew up in has a central brick chimney for this reason. When you put the fire out before going to bed you have a column of brick radiating throughout the night. It’s still pretty chilly in the morning but it works quite well.

Right, but it turns out the mortar fails more often than you would like and you'd get smoke & carbon monoxide leaking into houses from that central chimney, which is why that went away (or so I've heard)

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.

The problem, in my experience (grew up spending significant time in a 3 story country house made of stone with only one fireplace for heating), is that it gets warm close to the fire and whatever is touching the chimney, but the rest of the house gets colder because of the cold air drawn in by the fire. So very likely a net gain, but depending on where you sleep, it could get interesting at night.

Even worse, all that exhaust gas that goes up the chimney has to be replaced. And it's replaced by cold air from the outside coming through all the little books and crannies of your house.

I have seen slow combustion fireplaces still drawing in air from the room in front of them, leading to your exact comment.

Seems like it could be fixed with a simple design change.

But I am not a fireplace lawyer so I won't profess to know.

There are many different designs that have tried to solve the issue. Both from capturing the heat lost up the chimney and supplying combustion air from outside. They all come with downsides and ultimately forced air heating won out.

https://www.offgridquest.com/fload/homes-dwellings/heating-c...

Almost without comment. All I will say is that we have some friends in Germany living in the 'countryside' (as much as that's still a thing in densely populated Germany) that heat their main living area with one of these (way less elaborate design lol). My grandma had one of these sitting in the wall between kitchen (right next to the eating area) and the living room.

My parents have one of these in their holiday house by the sea (essentially an old farmhands dwelling). I can confirm that it heats the house up to blistering temperature even in the coldest winter if one wants. Other friends use a more modern design in their house which essentially heats up the whole house (I don't think they have any other heating except water heating)

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.

Not if they are in the attic. Also, my house has a subfloor. When the furnace and water heater were inside the part of the house you live in, they both had vents on the floor, so air used for combustion came from outside.

No, the issue is that the draw of the heated air up through the flue creates a negative pressure inside the home, which gets made up through all the little nooks and crannies around the house.

As a result, the room where the fireplace is will be warmer but the rest the house is typically colder.

Oh interesting. So you're saying it actually accelerates net heat loss to the environment?

Probably to a small extent but the more pronounced effect is the heat gradient. The rest of the house becoming quite a bit colder just sends you back to the fireplace, which is generally not a bad place to be, so overall it's not a major issue.

> so overall it's not a major issue

... unless the extra peripheral heat loss freezes pipes.

It does, and it creates a floor on the outside temperature where the heat from the stove is overcome by the losses of sucking in the cold air. This depends on the design of the stove. Some wood stoves pull down the firebox air from the outside to avoid this problem, but it is fairly unusual. There is a second heat exchanger with its own fan that circulates the inside air. The problem with this is that you still lose a lot of heat up the chimney.

Many fireplaces that HSE outside air sometimes put hot smoke out the intake. The intake probably wasn't designed for this so it is a fire hazzard. This can be avoided, but if you don't know how you probably didn't.

Then again Ben Franklin figured out how to make a fireplace that worked yet most don't.

> Some wood stoves pull down the firebox air from the outside to avoid this problem, but it is fairly unusual.

AFAIK in europe having outside air intake in stove is mandated by law. You can not use it, but all newly built houses have outside intake if someone was planning on adding wood stove. You also need to have proper vent near your stove, so even if it uses inside air, it will typically get it through that. I have automatic pellet burning furnace in basement for normal heating needs (it starts automatically when needed, uses 3 temperature sensors on floors and in basement) and wood stove for "romantic" purposes, but when it's fired, it heats up almost whole house and pellet stove sees that no more heating is needed. I have lots of leftover wood from construction phase, so wood stove will pay itself back from reduced use of pellet.

As for losing heat through chimney - properly mounted and operated wood stove doesn't lose that much heat through chimney. Most of them have long enough steel pipe from stove to chimney, which reuses some heat from exhaust and ventilation channels in chimney, which are heating incoming air.

I doubt this net-loss is the case for most new gas fireplaces with direct-vent exhaust systems, in which case the combustion air comes from the outside. This is what I have. Not sure how common these would be in Texas. It can also be used in the event of a power outage. (Minus the fan) [1]

[1] https://www.heatilator.com/owner-support/troubleshooting-and...

Yes. You’ve got a big hole in the wall/ceiling with a pressure differential blowing most of the heat up & out while sucking cold air in. Balanced improperly, you get a radiant heat area with rest subject to cold air.

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