7 ms·

My house uses a heat pump + oil-burning furnace. It gives a pretty good combination of efficiency, and ability to handle really cold weather.

toomuchtodo 4y ago
I think this is most of the way to what the future looks like: a high efficiency heat pump with cogeneration, so you can still burn propane or natural gas for heat and limited power to drive the heating system in an emergency (and if you don't have gas service to the premises, you have either a propane tank [1] or an exterior outlet to hook up outside). You must have a solution for when utility power is down for substantial periods of time. During the winter storm that just passed, a friend in the Midwest called that their house had no power and was rapidly cooling. The utility could provide no ETA to resolution. I walked them through (over the phone) safely enough backfeeding enough power from a gasoline generator (outside, with the extension cord run through a basement escape window) into their furnace circuit to bootstrap the furnace (and run the blower fan) to keep the house warm so that the pipes didn't freeze and burst. If the HVAC system had had a small battery and some way to generate power from the heat it was burning, the gasoline generator would've been unnecessary. Perhaps an integrated thermoelectric generator [2]? A standby generator isn't financially practical for most folks ($6k + install). (EDIT: to the safety folks out there possibly concerned, the furnace breaker and main breaker were tripped, and the meter was pulled to prevent any chance of harm to electrical linemen from inadvertently energizing the utility line; take no chances with safety, do not attempt this at home) [1] https://www.amerigas.com/about-propane/propane-tank-sizes https://www.amerigas.com/about-propane/propane-tank-sizes [2] https://patents.google.com/patent/US5427086A/en https://patents.google.com/patent/US5427086A/en
- Scoundreller 4y ago
  Problem is high efficiency furnaces/boilers require a powered vent, so they need quite a bit of power to operate. And then you’d need to circulate “cold” air/water against the heat exchangers. This usually adds up to several hundred watts.
- sokoloff 4y ago
  For others interested in preparing for a situation like this, here's a video laying out in reasonable detail what to do.* https://www.youtube.com/watch?v=1JNuovFpCpQ https://www.youtube.com/watch?v=1JNuovFpCpQ * I don't like that they skipped putting a bushing or an NM clamp on the back of the box into the furnace, but otherwise the video looked sound when I watched it a couple weeks ago.
  - jchw 4y ago
    I've been waiting to do this in the event of a power outage; that said, I'm really curious what the current draw of my furnace blower will wind up being. There is a label that suggests it has a peak draw of 8.5A, but that seems like a lot. Still, it seems like a nice backup plan in the event of an outage, even if I only have a couple kWh worth of battery storage.
    - a9h74j 4y ago
      Many furnaces use third-party controller boards with well-known suppliers. You might find in the furnace manual that there are different wire-to-board permutations to allow different fan (interior recirculating blower) speeds. From home testing a few years ago, I recall RMS currents 50%-80% of peak rated draw, but could be mistaken.
    - mikeyouse 4y ago
      What's the model number of your furnace / blower? I've been doing a ton of research in this area as I'm remodeling my place and have several furnaces and duct loops to deal with. From what I've seen so far, unless your unit is super old, the 8.5A is almost certainly just a 'peak' startup current that's overstated as well. Your blower should say something like "1/3 HP" and from there it's straightforward conversion of 1HP = ~750W so a 1/3HP would be 250W. On a 120v service, that's 2 Amp. With maybe 15% efficiency loss, at peak speed, the blower motor wouldn't be drawing more than 2.5A. It could/will draw more than that to start, but literally just for a second or two.
      - jchw 4y ago
- mynameishere 4y ago
  I don't know what's up with that, but the standard fix is to let the faucets trickle.
  - toomuchtodo 4y ago
    Challenging when you're on a well and your well pump requires power. Will your generator support 220V and the surge start a well pump requires? That surge is going to occur every X minutes to replenish the pressure tank as it depletes due to trickling. In this scenario, driving the 15A furnace circuit was a more simple fix. Something else to consider: electric pipe heat cable to keep pipes from freezing draws ~7 watts per foot, is quick to install, and easy to power if you've planned ahead.
    - mynameishere 4y ago
      I guess I must plead ignorance once again. Maybe flushing the pipes would be possible? I just know I would electrocute myself screwing with anything more powerful than a laptop battery.
      - sokoloff 4y ago
        I happen to have valves that would allow me to drain almost all of my house to prevent freezing, but that's not universally the case (and even in my case, I couldn't drain the hot water tank fully without power without letting it just flood the basement). Freezing pipes is one concern, though having heat for the humans is another pretty desirable thing, so if I could spend effort on something that would result in drained pipes and no heat or on something that would result in enough heat in the house to make that unnecessary, I'm going for option #2 every time.
        Marsymars 4y ago
        > (and even in my case, I couldn't drain the hot water tank fully without power without letting it just flood the basement). That doesn’t sound like it should be up to code? I’d expect building codes to require a floor drain where your water tank is.
- jabart 4y ago
  New homes should be built to better insulation standards. You have to solve so much and use so much energy to solve for a drafty house or lack of insulation on the outside walls. Newer homes are factoring in the R-value of 2x6s and finding ways to insulate those now. In this scenario, high efficiency heat pump with a backup gas fireplace. Those typically don't require any electricity to run as they can ignite off AA battery or a push button. My PC battery backups barely last 30 minutes on a wifi router because of conversion loss. Furnace fans also account for up to 1/3 of energy usage of a unit. Cogneration would add $5-10k to a home build versus a 50 gallon propane tank with a single emergency gas fireplace unit.
  - masklinn 4y ago
    If you've got wood available, you could also have a wood furnace as backup, and / or an actual fireplace (an efficient one ideally, possibly a masonry heater if you have the space and foundations to handle that load).
    - patentatt 4y ago
      This is a great solution too. I have a wood 'heatilator' (or fireplace insert) and during the recent cold snap in the Midwest I went through about 1/4 face cord of kiln-dried oak over 3 or 4 days (that's a lot by my standards). It kept the gas furnace mostly idling and the home warm (in the 80's by the fireplace actually, lol). Probably not exactly cost efficient with the cost of wood these days but I like being able to take some of the load off the gas furnace.
  - toomuchtodo 4y ago
    Most of the heat from a fireplace goes up the flue unfortunately. It’s one of the least efficient heating sources per the dept of energy (~15% efficient). A low tech solution is more thermal mass perhaps in high performance dwellings. Wood burning furnaces are a challenge because homeowners insurance providers don’t want to insure dwellings that use them (but will if certain conditions are met, such as it not being the primary hearing source, professionally installed, etc).
- lizknope 4y ago
  I was also without power last week for 6 hours. I have a SEER 18 heat pump for cooling which can reverse for heating in the winter but it also has a natural gas burner. Based on the installer's advice we set the system to use the heat pump if the outside air is 40F or above and switch to natural gas below 40F. The problem was that when the power was out the electronics in the system could not communicate with the thermostat in the house. My Nest thermostat literally said there was no system connected. I wish there was some kind of UPS to power those electronics and the blower fan.
  - jacquesm 4y ago
    Can't you just hook up a sizeable computer UPS for that purpose? That should run it for long enough to get you through most outages.
    - sokoloff 4y ago
      The heat pump will be a 240VAC load. Consumer-level computer UPSes in the US are 120VAC. The 24VAC transformer for the control circuitry will be on one of the 120VAC legs, but it's likely the installer didn't specifically wire it to allow partial powering of just the transformer and electronics board.
      - jacquesm 4y ago
        Hm... you might be able to get away with ordering a EU UPS then, those are 240V, you'll have to add a center tap transformer and maybe mess around a bit with it to get it to output 60 Hz (that will only improve efficiency).
        sokoloff 4y ago
        I think if you’re just looking to run the fossil fuel equipment from the UPS, you can do it by just ensuring that and all the transformers and controls are on that phase. That will take an HVAC person who knows who things work rather than just following colors on a wiring diagram. Probably easier and more supportable than trying to import and mod an out of region unit.
- throw0101c 4y ago
  > A standby generator isn't financially practical for most folks ($6k + install). An Honda EU2200i generator costs US$ 1400 (and less expensive generators can probably be found): * https://powerequipment.honda.com/generators/models/eu2200i https://powerequipment.honda.com/generators/models/eu2200i You also need an external plug, a cable going from that plug to a sub-panel, and a line going from the sub-panel to the main panel with an interlock device for safety, if you wish to avoid running extension cords. There are dual-fuel generators that can also use either gas/petrol or propane, and some tri-fuel generators that could also be connect to a natgas pipes (and conversion kits that can be added to propane-capable generators).
  - mindslight 4y ago
    The problem is that while all that electrical work is a weekend project for a DIYer, it's quite expensive to have a professional do it. So then you start bundling things (since I'm already paying thousands, maybe I'll just splurge for that Generac with the auto tranfer switch...) (FWIW, I believe there is an aftermarket propane conversion kit for the EU2200i. Converting a gasoline engine to run on propane is straightforward)
  - phil21 4y ago
    The Honda EU2200i can be aftermarket modded to run tri-fuel. I did it to mine just in case, and currently have it set to run propane. A simple swap of a small part will let it burn natural gas instead. I also like that I don't have gasoline to deal with - I can stock up a 20lb propane tanks and generally forget about it. Rotating gas is a giant pain if you keep enough on-hand for an outage of any appreciable amount of time.
    - toomuchtodo 4y ago
      Would you mind sharing a link to the part you mentioned?
      - sokoloff 4y ago
        https://www.amazon.com/Grenergy-Gasoline-Conversion-Generator-Inverter/dp/B08KG5H5MZ/ https://www.amazon.com/Grenergy-Gasoline-Conversion-Generato...
- alpos 4y ago
  Up in the northeast power goes out every winter. It also gets restored a lot faster than the midwest, personal experience, but the reliability of it going out at some point during the winter means that everyone has a wood stove and a backup generator. Portable ones are practical enough and wiring a couple of circuits and a plug for the generator is not cost prohibitive for most. What I've found in traveling the whole country for a few years is that local power generation or storage always forces you to consider just how little power you actually need. You can pretty much never just power the whole house, or even a whole RV. Even 50amps is ALOT of power and trying to provide that from solar/generator/batteries is incredibly expensive. So your real question is pretty much never going to be, "how do I power my whole house in an outage?" but rather, "What is absolutely essential to spend up to 3000w on?" and even then knowing that a generator putting out 3000w burns 20lbs of propane in about 4hrs and 3000w for 4hr on batteries would require 10 to 12 100ah lithium batteries at $350+ each. I still agree with you that super efficient heat pumps are the future without fossil fuels but that probably also has to come with greatly improved insulation values in almost all homes regardless of region. Think double the current DOE recommendations. If you're running on electricity, you will feel the cost of every bit of heat you lose through the walls, roof, and windows. More insulation is a one time cost versus monthly, it always makes sense in the long run. However, we'll need regulation to force home builders to invest in that instead of just adding unnecessary sqft that people never use but have to heat and cool anyway. For some reason people don't want to pay extra for a house that is well built and well insulated, they'd rather go with bigger is better even when it's already absurd, and builders have noticed this.
wmeredith 4y ago
Mine is the same with a gas furnace/heat pump combo. It's great.
jcadam 4y ago
My house uses a NatGas boiler and in-floor radiant heat. It also has wood stoves for those -20F (or worse) nights when I need a little supplemental heat (or the power is out and the main heating system is offline). A heat pump would be a waste up here in Alaska esp given I don't need A/C. Just opening the windows and running some fans in the summer tends to do the trick for cooling.
- throw0101c 4y ago
  > Just opening the windows and running some fans in the summer tends to do the trick for cooling. The problem with 'natural' ventilation is you also get things humidity, pollen, dust, etc coming in as well. One of the major advantages of mechanical ventilation (like HRV/ERVs, which cycle the air) is that things are tempered and filtered beforehand. Sometimes you also want to deal with individual variables: the temperature is fine, but the humidity is off.
  - jcadam 4y ago
    There's the expense of maintaining a central A/C, ductwork, etc., that I'd rather not deal with (not to mention electricity is expensive here). Yes, if the air outside is dirty (forest fires, volcanic eruption, etc.) you've got a point. HEPA filters can help some with this, I suppose. Humidity isn't usually a big issue here most days. If anything, it can be a bit dry (but not as dry as running an A/C would make it). Though, I do have a portable dehumidifier I use when I need to :)
  - a9h74j 4y ago
    Is filtering incoming air (for a mix) necessarily the norm, though? Even in the rare high-performance homes built on spec[ulation], my sense is that filtering incoming air might be omitted, in favor of a single filter acting on recirculation.
    - jcadam 4y ago
      And forced air can be quite dirty (dust/pollen/etc.) if you don't clean your ducts regularly.
euroderf 4y ago
My use case is similar. The oil furnace feeds hot water into a network of radiators. My design goal is to maximize the electricity outage that we can make it thru without frozen pipes, and it has to be on a budget (so no generator or giant UPS). The house is mostly unoccupied (a second home). Operation in an outage has to be fully automatic - it needs an automatic transfer switch I guess. The typical indoor temperature is just 5.5C (42F) - this does not leave much margin for the house to cool down during an outage when outside is like -5C (or -10 or -20). But it turn out that an oil pump and a water circulation pump do not draw THAT much power, so if I can run them off backup power (say, a new car battery plus an inverter), it should last for some time before ice has any chance to form.
pridkett 4y ago
I’ve got the same thing. I did a bunch of tests last year to figure out relative performance and costs of heating my house at various outside temperatures. This included doing fine grained electricity monitoring with an iotawatt and rough fuel oil usage using an ultrasonic sensor. Of course, now I’ve got a ton of data that I haven’t finished building my automation with. And, unfortunately, I’ve got an annoyingly bad Lennox iComfort for my heat pump thermostat and may have troubles building the automation anyway.

toomuchtodo 4y ago

I think this is most of the way to what the future looks like: a high efficiency heat pump with cogeneration, so you can still burn propane or natural gas for heat and limited power to drive the heating system in an emergency (and if you don't have gas service to the premises, you have either a propane tank [1] or an exterior outlet to hook up outside). You must have a solution for when utility power is down for substantial periods of time. During the winter storm that just passed, a friend in the Midwest called that their house had no power and was rapidly cooling. The utility could provide no ETA to resolution. I walked them through (over the phone) safely enough backfeeding enough power from a gasoline generator (outside, with the extension cord run through a basement escape window) into their furnace circuit to bootstrap the furnace (and run the blower fan) to keep the house warm so that the pipes didn't freeze and burst. If the HVAC system had had a small battery and some way to generate power from the heat it was burning, the gasoline generator would've been unnecessary. Perhaps an integrated thermoelectric generator [2]? A standby generator isn't financially practical for most folks ($6k + install). (EDIT: to the safety folks out there possibly concerned, the furnace breaker and main breaker were tripped, and the meter was pulled to prevent any chance of harm to electrical linemen from inadvertently energizing the utility line; take no chances with safety, do not attempt this at home) [1] https://www.amerigas.com/about-propane/propane-tank-sizes https://www.amerigas.com/about-propane/propane-tank-sizes [2] https://patents.google.com/patent/US5427086A/en https://patents.google.com/patent/US5427086A/en

Scoundreller 4y ago
Problem is high efficiency furnaces/boilers require a powered vent, so they need quite a bit of power to operate. And then you’d need to circulate “cold” air/water against the heat exchangers. This usually adds up to several hundred watts.
sokoloff 4y ago
For others interested in preparing for a situation like this, here's a video laying out in reasonable detail what to do.* https://www.youtube.com/watch?v=1JNuovFpCpQ https://www.youtube.com/watch?v=1JNuovFpCpQ * I don't like that they skipped putting a bushing or an NM clamp on the back of the box into the furnace, but otherwise the video looked sound when I watched it a couple weeks ago.
- jchw 4y ago
  I've been waiting to do this in the event of a power outage; that said, I'm really curious what the current draw of my furnace blower will wind up being. There is a label that suggests it has a peak draw of 8.5A, but that seems like a lot. Still, it seems like a nice backup plan in the event of an outage, even if I only have a couple kWh worth of battery storage.
  - a9h74j 4y ago
    Many furnaces use third-party controller boards with well-known suppliers. You might find in the furnace manual that there are different wire-to-board permutations to allow different fan (interior recirculating blower) speeds. From home testing a few years ago, I recall RMS currents 50%-80% of peak rated draw, but could be mistaken.
  - mikeyouse 4y ago
    What's the model number of your furnace / blower? I've been doing a ton of research in this area as I'm remodeling my place and have several furnaces and duct loops to deal with. From what I've seen so far, unless your unit is super old, the 8.5A is almost certainly just a 'peak' startup current that's overstated as well. Your blower should say something like "1/3 HP" and from there it's straightforward conversion of 1HP = ~750W so a 1/3HP would be 250W. On a 120v service, that's 2 Amp. With maybe 15% efficiency loss, at peak speed, the blower motor wouldn't be drawing more than 2.5A. It could/will draw more than that to start, but literally just for a second or two.
    - jchw 4y ago
mynameishere 4y ago
I don't know what's up with that, but the standard fix is to let the faucets trickle.
- toomuchtodo 4y ago
  Challenging when you're on a well and your well pump requires power. Will your generator support 220V and the surge start a well pump requires? That surge is going to occur every X minutes to replenish the pressure tank as it depletes due to trickling. In this scenario, driving the 15A furnace circuit was a more simple fix. Something else to consider: electric pipe heat cable to keep pipes from freezing draws ~7 watts per foot, is quick to install, and easy to power if you've planned ahead.
  - mynameishere 4y ago
    I guess I must plead ignorance once again. Maybe flushing the pipes would be possible? I just know I would electrocute myself screwing with anything more powerful than a laptop battery.
    - sokoloff 4y ago
      I happen to have valves that would allow me to drain almost all of my house to prevent freezing, but that's not universally the case (and even in my case, I couldn't drain the hot water tank fully without power without letting it just flood the basement). Freezing pipes is one concern, though having heat for the humans is another pretty desirable thing, so if I could spend effort on something that would result in drained pipes and no heat or on something that would result in enough heat in the house to make that unnecessary, I'm going for option #2 every time.
      - Marsymars 4y ago
        > (and even in my case, I couldn't drain the hot water tank fully without power without letting it just flood the basement). That doesn’t sound like it should be up to code? I’d expect building codes to require a floor drain where your water tank is.
jabart 4y ago
New homes should be built to better insulation standards. You have to solve so much and use so much energy to solve for a drafty house or lack of insulation on the outside walls. Newer homes are factoring in the R-value of 2x6s and finding ways to insulate those now. In this scenario, high efficiency heat pump with a backup gas fireplace. Those typically don't require any electricity to run as they can ignite off AA battery or a push button. My PC battery backups barely last 30 minutes on a wifi router because of conversion loss. Furnace fans also account for up to 1/3 of energy usage of a unit. Cogneration would add $5-10k to a home build versus a 50 gallon propane tank with a single emergency gas fireplace unit.
- masklinn 4y ago
  If you've got wood available, you could also have a wood furnace as backup, and / or an actual fireplace (an efficient one ideally, possibly a masonry heater if you have the space and foundations to handle that load).
  - patentatt 4y ago
    This is a great solution too. I have a wood 'heatilator' (or fireplace insert) and during the recent cold snap in the Midwest I went through about 1/4 face cord of kiln-dried oak over 3 or 4 days (that's a lot by my standards). It kept the gas furnace mostly idling and the home warm (in the 80's by the fireplace actually, lol). Probably not exactly cost efficient with the cost of wood these days but I like being able to take some of the load off the gas furnace.
- toomuchtodo 4y ago
  Most of the heat from a fireplace goes up the flue unfortunately. It’s one of the least efficient heating sources per the dept of energy (~15% efficient). A low tech solution is more thermal mass perhaps in high performance dwellings. Wood burning furnaces are a challenge because homeowners insurance providers don’t want to insure dwellings that use them (but will if certain conditions are met, such as it not being the primary hearing source, professionally installed, etc).
lizknope 4y ago
I was also without power last week for 6 hours. I have a SEER 18 heat pump for cooling which can reverse for heating in the winter but it also has a natural gas burner. Based on the installer's advice we set the system to use the heat pump if the outside air is 40F or above and switch to natural gas below 40F. The problem was that when the power was out the electronics in the system could not communicate with the thermostat in the house. My Nest thermostat literally said there was no system connected. I wish there was some kind of UPS to power those electronics and the blower fan.
- jacquesm 4y ago
  Can't you just hook up a sizeable computer UPS for that purpose? That should run it for long enough to get you through most outages.
  - sokoloff 4y ago
    The heat pump will be a 240VAC load. Consumer-level computer UPSes in the US are 120VAC. The 24VAC transformer for the control circuitry will be on one of the 120VAC legs, but it's likely the installer didn't specifically wire it to allow partial powering of just the transformer and electronics board.
    - jacquesm 4y ago
      Hm... you might be able to get away with ordering a EU UPS then, those are 240V, you'll have to add a center tap transformer and maybe mess around a bit with it to get it to output 60 Hz (that will only improve efficiency).
      - sokoloff 4y ago
        I think if you’re just looking to run the fossil fuel equipment from the UPS, you can do it by just ensuring that and all the transformers and controls are on that phase. That will take an HVAC person who knows who things work rather than just following colors on a wiring diagram. Probably easier and more supportable than trying to import and mod an out of region unit.
throw0101c 4y ago
> A standby generator isn't financially practical for most folks ($6k + install). An Honda EU2200i generator costs US$ 1400 (and less expensive generators can probably be found): * https://powerequipment.honda.com/generators/models/eu2200i https://powerequipment.honda.com/generators/models/eu2200i You also need an external plug, a cable going from that plug to a sub-panel, and a line going from the sub-panel to the main panel with an interlock device for safety, if you wish to avoid running extension cords. There are dual-fuel generators that can also use either gas/petrol or propane, and some tri-fuel generators that could also be connect to a natgas pipes (and conversion kits that can be added to propane-capable generators).
- mindslight 4y ago
  The problem is that while all that electrical work is a weekend project for a DIYer, it's quite expensive to have a professional do it. So then you start bundling things (since I'm already paying thousands, maybe I'll just splurge for that Generac with the auto tranfer switch...) (FWIW, I believe there is an aftermarket propane conversion kit for the EU2200i. Converting a gasoline engine to run on propane is straightforward)
- phil21 4y ago
  The Honda EU2200i can be aftermarket modded to run tri-fuel. I did it to mine just in case, and currently have it set to run propane. A simple swap of a small part will let it burn natural gas instead. I also like that I don't have gasoline to deal with - I can stock up a 20lb propane tanks and generally forget about it. Rotating gas is a giant pain if you keep enough on-hand for an outage of any appreciable amount of time.
  - toomuchtodo 4y ago
    Would you mind sharing a link to the part you mentioned?
    - sokoloff 4y ago
      https://www.amazon.com/Grenergy-Gasoline-Conversion-Generator-Inverter/dp/B08KG5H5MZ/ https://www.amazon.com/Grenergy-Gasoline-Conversion-Generato...
alpos 4y ago
Up in the northeast power goes out every winter. It also gets restored a lot faster than the midwest, personal experience, but the reliability of it going out at some point during the winter means that everyone has a wood stove and a backup generator. Portable ones are practical enough and wiring a couple of circuits and a plug for the generator is not cost prohibitive for most. What I've found in traveling the whole country for a few years is that local power generation or storage always forces you to consider just how little power you actually need. You can pretty much never just power the whole house, or even a whole RV. Even 50amps is ALOT of power and trying to provide that from solar/generator/batteries is incredibly expensive. So your real question is pretty much never going to be, "how do I power my whole house in an outage?" but rather, "What is absolutely essential to spend up to 3000w on?" and even then knowing that a generator putting out 3000w burns 20lbs of propane in about 4hrs and 3000w for 4hr on batteries would require 10 to 12 100ah lithium batteries at $350+ each. I still agree with you that super efficient heat pumps are the future without fossil fuels but that probably also has to come with greatly improved insulation values in almost all homes regardless of region. Think double the current DOE recommendations. If you're running on electricity, you will feel the cost of every bit of heat you lose through the walls, roof, and windows. More insulation is a one time cost versus monthly, it always makes sense in the long run. However, we'll need regulation to force home builders to invest in that instead of just adding unnecessary sqft that people never use but have to heat and cool anyway. For some reason people don't want to pay extra for a house that is well built and well insulated, they'd rather go with bigger is better even when it's already absurd, and builders have noticed this.

wmeredith 4y ago

Mine is the same with a gas furnace/heat pump combo. It's great.

jcadam 4y ago

My house uses a NatGas boiler and in-floor radiant heat. It also has wood stoves for those -20F (or worse) nights when I need a little supplemental heat (or the power is out and the main heating system is offline). A heat pump would be a waste up here in Alaska esp given I don't need A/C. Just opening the windows and running some fans in the summer tends to do the trick for cooling.

throw0101c 4y ago
> Just opening the windows and running some fans in the summer tends to do the trick for cooling. The problem with 'natural' ventilation is you also get things humidity, pollen, dust, etc coming in as well. One of the major advantages of mechanical ventilation (like HRV/ERVs, which cycle the air) is that things are tempered and filtered beforehand. Sometimes you also want to deal with individual variables: the temperature is fine, but the humidity is off.
- jcadam 4y ago
  There's the expense of maintaining a central A/C, ductwork, etc., that I'd rather not deal with (not to mention electricity is expensive here). Yes, if the air outside is dirty (forest fires, volcanic eruption, etc.) you've got a point. HEPA filters can help some with this, I suppose. Humidity isn't usually a big issue here most days. If anything, it can be a bit dry (but not as dry as running an A/C would make it). Though, I do have a portable dehumidifier I use when I need to :)
- a9h74j 4y ago
  Is filtering incoming air (for a mix) necessarily the norm, though? Even in the rare high-performance homes built on spec[ulation], my sense is that filtering incoming air might be omitted, in favor of a single filter acting on recirculation.
  - jcadam 4y ago
    And forced air can be quite dirty (dust/pollen/etc.) if you don't clean your ducts regularly.

euroderf 4y ago

My use case is similar. The oil furnace feeds hot water into a network of radiators. My design goal is to maximize the electricity outage that we can make it thru without frozen pipes, and it has to be on a budget (so no generator or giant UPS). The house is mostly unoccupied (a second home). Operation in an outage has to be fully automatic - it needs an automatic transfer switch I guess. The typical indoor temperature is just 5.5C (42F) - this does not leave much margin for the house to cool down during an outage when outside is like -5C (or -10 or -20). But it turn out that an oil pump and a water circulation pump do not draw THAT much power, so if I can run them off backup power (say, a new car battery plus an inverter), it should last for some time before ice has any chance to form.

pridkett 4y ago

I’ve got the same thing. I did a bunch of tests last year to figure out relative performance and costs of heating my house at various outside temperatures. This included doing fine grained electricity monitoring with an iotawatt and rough fuel oil usage using an ultrasonic sensor. Of course, now I’ve got a ton of data that I haven’t finished building my automation with. And, unfortunately, I’ve got an annoyingly bad Lennox iComfort for my heat pump thermostat and may have troubles building the automation anyway.