Question about firebox and flue gasses and particulates

[habanero]

Greetings. I'm new to hearth.com but have been reading posts for several weeks.

I'm researching wood heat as a possibility for a friend's home and have a technical question I haven't seen addressed on hearth.com, or anywhere online.

My question is, does anyone know of studies or research data which compare the combustion gasses and particulates in both the firebox and the exhaust of EPA 2020 vs older EPA certified stoves? In particular I'm wondering how the more efficient EPA 2020 designs, with lower particulate emissions, effect the composition of gasses and particulates in the stove firebox. One concern is that the processes which produce lower particulates exiting the stove may increase toxic gasses and particulates in the firebox, and as a result, in the indoor air.

The reason for such a nit-picky technical question is that our friend's family has several members with rare/odd medical conditions which are aggravated by a number of things, including combustion byproducts. Their house is currently heated by an LP-gas-fired, forced air system. Unfortunately, gas-fired appliances (any gas-fired appliance, not just their HVAC system) trigger significant reactions; so they're asking about wood heat as a possible alternative. They've considered (and tried) electric heat, but with prices in their area ranging from $0.27-$0.32 per kWh, the cost per month is astronomical. The affected family members report that when staying in homes heated only with well-maintained, competently-operated, older EPA-certified wood stoves, symptoms are "minimal" to "tolerable". Another plus for them is that they have access to free firewood. (Mostly oak, madrone, manzanita, fir and pine.)

I'm speculating that stoves which meet the EPA 2020 requirements may actually produce and retain more toxic gasses and particulates in the firebox than older, higher-emissions stoves. Knowing whether or not this is true, and to what extent, is likely to have an impact on which stoves they should consider using in their home.

Thanks in advance for your input.

 

[bholler]

Neither pre or post 2020 epa stoves should be putting anything into the interior of the house if they are installed and operated properly. But the gas appliances should not be either.

 

[Highbeam]

Be careful not to confuse emissions and efficiency. They are not related. A really good design has high efficiency and low emissions but many are severely lopsided. I own examples of that with a dirty but high efficiency cat stove and a clean but low efficiency noncat.

The 2020 regs are about getting low emissions.

 

[bholler]

Be careful not to confuse emissions and efficiency. They are not related. A really good design has high efficiency and low emissions but many are severely lopsided. I own examples of that with a dirty but high efficiency cat stove and a clean but low efficiency noncat.

The 2020 regs are about getting low emissions.

Well they are somewhat related but it is not at all a direct correlation.

 

[mar13]

I remember reading some scientific article that stated (if I recall correctly) that the greatest cause of indoor pollution from properly set up woodstoves was from cleaning the ash out of the stove, not the actual fire. I unsuccessfully tried to find that article a second time. I searched scholar.google.com again, with no luck. So it's probably best I just retract what I wrote earlier. I really wish I could find that article again.

In general, I think trying wood heat would be an expensive gamble for highly sensitive people. The wood, alone, could bring issues. California utilities do have reduced electric rates for those with medical conditions or low income. I think the rates are also lower (or rate tiers adjusted) for those who use electricity as their main heat source.

 

[Socratic Monologue]

Neither pre or post 2020 epa stoves should be putting anything into the interior of the house if they are installed and operated properly. But the gas appliances should not be either.

I agree. Though a wood stove can send a bit of firebox air into the room during a clumsy reload, a condensing gas furnace does not affect indoor air in the very least, since the entire combustion circuit is sealed off from the interior of the house. If there is some detectable air quality issue relating to a gas furnace, the best advice would be to repair or replace the furnace.

 

[Mech e]

It is more likely that their current lp furnace is releasing particulates lodged in the ductwork into the air. If that is the case, a wood stove will definitely add ash dust to the room, especially when cleaning.

 

[Socratic Monologue]

It is more likely that their current lp furnace is releasing particulates lodged in the ductwork into the air. If that is the case, a wood stove will definitely add ash dust to the room, especially when cleaning.

I've never had ducts cleaned, but at Thanksgiving dinner some friends were talking about how they had it done recently, were amazed at how much crud was removed, and thought that afterwards there was improvement in the dust situation in the house.

 

[peakbagger]

My guess is that forced hot air heat is probably the worst way to heat for people with sensitivities to various triggers. Inherently the lungs and sinuses are less effective at capturing and filtering airborn contaminants in low humidity conditions and the ductwork is notorious for collecting dust. Note the dust is partially composed of dead skin and hair from the occupants of the house and various mites and microscopic critters can live in these deposits and give off allergens. A heated building inherently is at negative pressure compared to outside and in cold weather the incoming air is far drier than the interior air. There are energy recovery devices that can reduce this negative pressure and bring in outside air recovering energy and moisture from the interior air but in cold climates generally the recover units only recover heat. Add in an internal combustion source and that also sucks in air unless its equipped with an outdoor air kit.

My guess is low temperature radiant heat is probably the best bet using an external source of energy. If they are in an area where the temps stay above -5 F air to water heat pumps are starting to become viable for supplying heat to low temperature radiant emitters. The COP varies with temperature but its generally two to three times more efficient than straight electric heat. I recently noticed that the state of VT is starting to pay incentives for installing these units and although I am still not thrilled by the depth of manufacturers they are out there.

As for a EPA stove putting out more intermediate pollutants I would not worry. Barring NOx regulations the best way to a clean burn is hot with adequate air which is pretty well how a 2020 stove meets the limits. There are various studies that blame generic wood stoves for higher rates of pollution but what type and how they are operated is generally not called out. Hopefully they have electric appliances as LP stoves are definitely a source of indoor air pollution.

 

[SpaceBus]

I agree. Though a wood stove can send a bit of firebox air into the room during a clumsy reload, a condensing gas furnace does not affect indoor air in the very least, since the entire combustion circuit is sealed off from the interior of the house. If there is some detectable air quality issue relating to a gas furnace, the best advice would be to repair or replace the furnace.

Or the issue is more than likely on the air handling side of things and there is mold in the house. Tight house + outdoor allergies + forced air = respiratory issues. Even worse with indoor allergies. Wood stoves are usually better for folks with allergies/sensitive respiratory issues since they force outside air into the house when outdoor allergens are lowest. The house needs a serious air quality inspection, a filter change at bare minimum. Most states offer assistance for those with income issues.

I also have a sensitive respiratory system that is agitated by smoke, but I also have two stoves. The longer I go without subjecting myself to a forced air system the better I have felt.

 

[Socratic Monologue]

mold in the house.

It might be that the differences these folks are experiencing are not entirely due to the difference in heating systems between the houses, but simply the houses themselves (i.e. one of them has more mold than the other).

A difference in mold growth in a house may be secondary to a difference in heat source, though, since homes heated with wood are more likely to run a lower humidity in winter (unless they provide outdoor air for combustion like a modern gas furnace does), which would hinder mold growth inside the house.

 

[danham]

Good answers from everyone. I'd only add that gas cookstoves -- specifically the oven -- are gross polluters. Most are not vented to the outside and are often very badly adjusted when installed, resulting in lots of carbon monoxide being produced. So the houses your friends ID as having gas furnaces are likley to also have a gas range.

I learned about this the hard way when cooking a turkey for many hours for Christmas one cold year and we had several family members complain of headaches. I checked our CO detector and it was just about to sound its alarm. Later I checked the oven burner and it had a weak orange flame and the air shutters were almost fully closed. But even with that fixed there is no code requirement for a vent or chimney. If you Google "gas oven air pollution" you will see info from California experts warning about this.

-dan

 

[EbS-P]

Just few thoughts on my personal experience. Burning wood is dirty. And flue gas is nasty. I can smell it every time I reload at the far end of the house for at least 10-15 minutes and this is with no visible smoke spilling.

Inevitably firewood stored outside will have mold and fungus spores that will be carried into the house. burning bio bricks might lessen the mold and fungus.
I just had a quote to replace all my ductwork. It was within 1000$ of what I paid to have my stove and have it installed. There are plenty of air filtering devices that can be installed in ductwork.
With out know any specifics about the origins of what is causing the issues it seems like a bit of a gamble. History says they can tolerate a wood stove. When it comes to real heath impacts I would want a little more knowledge to make an informed decision.

2020 epa va epa— I cant see how cutting the particulate emissions in have would have any effects on the chemical composition of the byproducts. Higher combustion temps could mean fewer larger molecules I guess. Creosote is a carcinogen. You can’t start a cold stove without making some. You can’t clean a stove without increasing your exposure level to those particles.
My quick googling didn’t come back with any relevant research.

i like the idea of air to water heat pump.
Evan

 

[Socratic Monologue]

2020 epa va epa— I cant see how cutting the particulate emissions in have would have any effects on the chemical composition of the byproducts. Higher combustion temps could mean fewer larger molecules I guess.

I don't know the exact changes for 2020, but EPA regs also deal with CO and NOx, I believe.

 

[Smokepole]

Greetings. I'm new to hearth.com but have been reading posts for several weeks.

I'm researching wood heat as a possibility for a friend's home and have a technical question I haven't seen addressed on hearth.com, or anywhere online.

My question is, does anyone know of studies or research data which compare the combustion gasses and particulates in both the firebox and the exhaust of EPA 2020 vs older EPA certified stoves? In particular I'm wondering how the more efficient EPA 2020 designs, with lower particulate emissions, effect the composition of gasses and particulates in the stove firebox. One concern is that the processes which produce lower particulates exiting the stove may increase toxic gasses and particulates in the firebox, and as a result, in the indoor air.

The reason for such a nit-picky technical question is that our friend's family has several members with rare/odd medical conditions which are aggravated by a number of things, including combustion byproducts. Their house is currently heated by an LP-gas-fired, forced air system. Unfortunately, gas-fired appliances (any gas-fired appliance, not just their HVAC system) trigger significant reactions; so they're asking about wood heat as a possible alternative. They've considered (and tried) electric heat, but with prices in their area ranging from $0.27-$0.32 per kWh, the cost per month is astronomical. The affected family members report that when staying in homes heated only with well-maintained, competently-operated, older EPA-certified wood stoves, symptoms are "minimal" to "tolerable". Another plus for them is that they have access to free firewood. (Mostly oak, madrone, manzanita, fir and pine.)

I'm speculating that stoves which meet the EPA 2020 requirements may actually produce and retain more toxic gasses and particulates in the firebox than older, higher-emissions stoves. Knowing whether or not this is true, and to what extent, is likely to have an impact on which stoves they should consider using in their home.

Thanks in advance for your input.

I believe any solid fuel device that is designed to exhaust its flue gases
toward the door where you reload will pollute your house.

 

[habanero]

I think the rates are also lower (or rate tiers adjusted) for those who use electricity as their main heat source.

I haven't heard this before. Thanks for the tip. I'll pass it on to our friends. Are you referring to PG&E?

 

[habanero]

Thanks for all of your input and suggestions.

My including a bit of information on our friends' combustion-byproducts-related health issues may have obscured my original question. I’ll reiterate here for clarity:
“Does anyone know of studies or research data which compare the combustion gasses and particulates in both the firebox and the exhaust of EPA 2020 vs older EPA certified stoves?”

I’ve attached a few pages from a 1997 EPA report on woodsmoke that gives an example of what I’m looking for. Here's a link to the document on the EPA site: https://nepis.epa.gov/Exe/ZyPDF.cgi/2000IK0H.PDF?Dockey=2000IK0H.PDF

 

[habanero]

A really good design has high efficiency and low emissions but many are severely lopsided. I own examples of that with a dirty but high efficiency cat stove and a clean but low efficiency noncat.

The 2020 regs are about getting low emissions.

Good points. Can you give examples of high efficiency and low emissions wood stoves? Would England's Stove Works' "Madison" (models 15-SSW01, 50-SHSSW01, and 50-TRSSW01) qualify? It's rated at 72% HHV (78% LHV) , with 1.9 grams/hour emissions.

 

[habanero]

My guess is that forced hot air heat is probably the worst way to heat for people with sensitivities to various triggers. Inherently the lungs and sinuses are less effective at capturing and filtering airborn contaminants in low humidity conditions and the ductwork is notorious for collecting dust. Note the dust is partially composed of dead skin and hair from the occupants of the house and various mites and microscopic critters can live in these deposits and give off allergens. A heated building inherently is at negative pressure compared to outside and in cold weather the incoming air is far drier than the interior air. There are energy recovery devices that can reduce this negative pressure and bring in outside air recovering energy and moisture from the interior air but in cold climates generally the recover units only recover heat. Add in an internal combustion source and that also sucks in air unless its equipped with an outdoor air kit.

My guess is low temperature radiant heat is probably the best bet using an external source of energy. If they are in an area where the temps stay above -5 F air to water heat pumps are starting to become viable for supplying heat to low temperature radiant emitters. The COP varies with temperature but its generally two to three times more efficient than straight electric heat. I recently noticed that the state of VT is starting to pay incentives for installing these units and although I am still not thrilled by the depth of manufacturers they are out there.

As for a EPA stove putting out more intermediate pollutants I would not worry. Barring NOx regulations the best way to a clean burn is hot with adequate air which is pretty well how a 2020 stove meets the limits. There are various studies that blame generic wood stoves for higher rates of pollution but what type and how they are operated is generally not called out. Hopefully they have electric appliances as LP stoves are definitely a source of indoor air pollution.

Thanks for the radiant heat suggestion. They've considered it but decided against it for a number of reasons. Maybe after this discussion they'll be reconsidering...

"Hopefully they have electric appliances..."
Yes. All electric, except for the heater, which is on the exterior of the home.

By "...energy recovery devices that can reduce this negative pressure and bring in outside air recovering energy and moisture from the interior air" are you referring to an "Energy Recovery Ventilator" (ERV)?

 

[habanero]

Or the issue is more than likely on the air handling side of things and there is mold in the house. Tight house + outdoor allergies + forced air = respiratory issues. Even worse with indoor allergies. Wood stoves are usually better for folks with allergies/sensitive respiratory issues since they force outside air into the house when outdoor allergens are lowest. The house needs a serious air quality inspection, a filter change at bare minimum. Most states offer assistance for those with income issues.

I also have a sensitive respiratory system that is agitated by smoke, but I also have two stoves. The longer I go without subjecting myself to a forced air system the better I have felt.

They had professional mold testing/inspection done a few years ago. The house was mold-free. (In the 1800s our region was sometimes called "The Great Northern Desert". Pretty dry.) They've also got a number of large air purifiers running 24/7. I'm guessing they regularly change their HVAC system filters.

It is more likely that their current lp furnace is releasing particulates lodged in the ductwork into the air. If that is the case, a wood stove will definitely add ash dust to the room, especially when cleaning.

Our friend's medical conditions aren't respiratory or allergen related. As I understand it, they are genetically-inherited immune system issues. For some reason combustion byproducts cause the immune system to malfunction.

 

[habanero]

The wood, alone, could bring issues.

Good point. Some local softwoods contain a fair amount of terpene. I'm not sure about local hardwoods, though I've read recently that terpene is present in the sapwood of hardwoods as well. I wonder how seasoning firewood alters terpene and other VOC levels? I'll pass your suggestions on to our friends.

 

[habanero]

I believe any solid fuel device that is designed to exhaust its flue gases
toward the door where you reload will pollute your house.

Interesting point. Do you know of any designs or brands/models that don't direct flue gases toward the door? The few cutaway diagrams I've seen of EPA-compliant non-catalytic stoves all seem to direct the flow of gases toward the door. The attached diagram is typical of what I've seen. (Diagram source: small-cabin.com)

 

[peakbagger]

Thanks for the radiant heat suggestion. They've considered it but decided against it for a number of reasons. Maybe after this discussion they'll be reconsidering...

"Hopefully they have electric appliances..."
Yes. All electric, except for the heater, which is on the exterior of the home.

By "...energy recovery devices that can reduce this negative pressure and bring in outside air recovering energy and moisture from the interior air" are you referring to an "Energy Recovery Ventilator" (ERV)?

Yes, but a specific type that recovers latent as well as sensible heat. That style recovers moisture in the air so it does not dry out the interior air as much. This style does not work well in below freezing climates.

 

[SpaceBus]

A stove with a well established draft won't allow combustion products back into the house. At least my stoves don't, and they also have air inelts on the doors without any way to connect an outside air. My wood cooker will make a mess if I try to clean it with a cold flue (exterior) but my wood stove does not due to the interior chimney.

 

[Socratic Monologue]

Interesting point. Do you know of any designs or brands/models that don't direct flue gases toward the door? The few cutaway diagrams I've seen of EPA-compliant non-catalytic stoves all seem to direct the flow of gases toward the door. The attached diagram is typical of what I've seen. (Diagram source: small-cabin.com)

I think all tube style EPA stoves have a glass front door, and in virtue of that glass have 'airwash' flow directed toward that glass. I don't know about the design of cat stoves.

Some stoves (Hearthstone Heritage) also have a side door that is typically used for loading. It is a solid door that has no airwash directed toward it. Our Heritage is a nice stove, and works well, but I wouldn't want to heat 24/7 with it.

Edit to add: the 2020 Heritage is a hybrid (tube+cat), but has the same side door design. Might be a little better for daily heating use with the added cat, but I don't know that anyone here even owns one of these yet.