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> 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 le

> 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?

jcims 6y ago
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.
- dwohnitmok 6y ago
  Oh interesting. So you're saying it actually accelerates net heat loss to the environment?
  - jcims 6y ago
    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.
    - KMag 6y ago
      > so overall it's not a major issue ... unless the extra peripheral heat loss freezes pipes.
  - jandrese 6y ago
    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.
    - bluGill 6y ago
      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.
    - yetihehe 6y ago
      > 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.
JonathonW 6y ago
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.
- AuthorizedCust 6y ago
  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.
ctdonath 6y ago
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.
ip26 6y ago
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.
- dwohnitmok 6y ago
  Ah the only heat exchange being radiant makes total sense. Thanks!
- gowld 6y ago
  Why don't we run radiator water pipes across the chimney, to bring that heat back to the house?
  - Jtsummers 6y ago
    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.
  - mbreese 6y ago
    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 https://en.m.wikipedia.org/wiki/Franklin_stove
  - mikestew 6y ago
    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.
brandon272 6y ago
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-faqs/power-outage https://www.heatilator.com/owner-support/troubleshooting-and...

jcims 6y ago

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.

dwohnitmok 6y ago
Oh interesting. So you're saying it actually accelerates net heat loss to the environment?
- jcims 6y ago
  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.
  - KMag 6y ago
    > so overall it's not a major issue ... unless the extra peripheral heat loss freezes pipes.
- jandrese 6y ago
  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.
  - bluGill 6y ago
    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.
  - yetihehe 6y ago
    > 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.

JonathonW 6y ago

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.

AuthorizedCust 6y ago
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.

ctdonath 6y ago

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.

ip26 6y ago

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.

dwohnitmok 6y ago
Ah the only heat exchange being radiant makes total sense. Thanks!
gowld 6y ago
Why don't we run radiator water pipes across the chimney, to bring that heat back to the house?
- Jtsummers 6y ago
  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.
- mbreese 6y ago
  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 https://en.m.wikipedia.org/wiki/Franklin_stove
- mikestew 6y ago
  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.

brandon272 6y ago

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-faqs/power-outage https://www.heatilator.com/owner-support/troubleshooting-and...