Why doesn't Regency use outside combustion air in its wood inserts?

[chipster96]

I'm interested in the i2400 wood burning insert, but was surprised to hear from a Regency rep that none of their wood inserts can be directly hooked up to outside air.

I thought that preventing already-warmed indoor air from going up the chimney was one of the most important efficiency steps.

 

[michaelryba]

Your post had me thinking the same & promped me to do some digging on this site.
The article below has info on house & fireplace design.
My 80 yr old house has a less-than-ideal design that produces smoke spillage for my currently open hearth.
Outside combustion air is a band-aid for homes built with a fireplace as an afterthought (like mine).
Modern inserts don't use anyway near the amount of air that open hearths do & run with the door closed.
the article from this website:
https://www.hearth.com/econtent/index.php/wiki/Best_Practices_for_Fireplace_installations/

 

[jtp10181]

Why? Because they are useless. Its not going to be 100% air tight so you are just cutting another hole in your wall to let cold in. In cold climates like up here its terrible. I can't think of one single wood insert we have installed with outside air (all the inserts we sell have it as an option I think). Out of the few pellet stoves we have done outside air that is nothing but trouble also, one we ended up ripping off because it was letting so much cold in.

 

[joesat78]

I thought about this a lot and finally concluded that OAK is very little use. Think of the system as a whole.

Whether you have OAK or not, you still need the same amount of fresh air to burn the wood. Without OAK, you will be taking the warm air and heat it, your blower will extract the heat and send the remaining up the chimney. Now, with OAK you will get fresh air from outside that would be COLD. You still need to warm that air to "sufficient temperature" so as to extract the heat with the help of a blower.

The heat loss will be almost the same in both the cases. The only positive impact OAK might have is it might reduce the draft from creaky areas in the house.

 

[begreen]

I'm not siding one side of the fence or the other because I don't have a lot of personal experience with this. But it seems pretty clear that the combustion air has to be replaced from somewhere. And a big stove can consume a fair amount of air when it's burning. This creates a slight vacuum. The heat loss comes from the cold air that infiltrates into the house to replace the interior warm air that the stove is burning and exhausting out of the house. Now as to which is more efficient, I'll leave it up to those with more experience. But there are some basement installations where this is the best way to run the stove due to it being a low pressure zone to start with.

 

[karl]

I have outside air on my insert and I'm quite happy with it. I never ran it with out the outside air, so I have nothing to compare it to. Mine doesn't let any cold air into the house.

 

[burntime]

Comparing my old pre epa and the new hampton, the old used lots of air. The outer extremeties were cold. With the new it spends all its time choked down. No major loss

 

[oconnor]

I'm not siding one side of the fence or the other because I don't have a lot of personal experience with this. But it seems pretty clear that the combustion air has to be replaced from somewhere. And a big stove can consume a fair amount of air when it's burning. This creates a slight vacuum. The heat loss comes from the cold air that infiltrates into the house to replace the interior warm air that the stove is burning and exhausting out of the house. Now as to which is more efficient, I'll leave it up to those with more experience. But there are some basement installations where this is the best way to run the stove due to it being a low pressure zone to start with.

Does anyone have a measure on how much air is used by an EPA stove? the only number I've seen is 10-25 CFM from Woodheat.org, but no source is given for the info. If that number is right, it is a small amount of air in view of the whole of air infiltaration in even a new, tight, house.

 

[thechimneysweep]

I think the 10-25 CFM outflow rate dates back to the pre-epa airtights which could be (and often were) turned down to smolder range and didn't have separate intakes for secondary combustion air. The range I've seen for EPA stoves is 15-40 cfm.

This seems to be an insignificant outflow rate, until you do the math. Even at 25 cfm, a woodstove chimney will evacuate a 1,000 sq.ft. house with 8' ceilings about five times per day. And draw in 5 housefulls of Winter-temperature replacement air from outside.

 

[begreen]

I know when the big 6 is fully loaded you can hear her drawing the air in gulps. And I'm certain if I had a 3" muffin fan blowing in 40 cfm of outside air, I'd notice it quickly. It's the distributed nature of the air infiltration that makes it seem innocuous.

 

[oconnor]

One thing I'll point out here is that many folks hear/see these numbers and think they are large amounts of air, or that they are not acceptable, and they cause massive heat loss thru infiltration directly attributed to vented gasses from the stove. I'm inclined to see them as quite small numbers over all.

By way of example, my house before renovations was rated at 8 air changes an hour ( 192 complete changes per day) and after air sealing and new windows, it dropped to 3.8 air changes per hour (91.2 per day). At 25 CFM in a 1000sqft home, we are talking 0.2 air changes per hour, the difference overall is negligible, and given the times when it is downright difficult to get an OAK connected (my insert in an internal brick fireplace for example) the effort can likely be spent elsewhere for much better returns. BTW, at 3.8 air changes an hour, my home is in the top 10% of homes of it's age and construction for air leakage (1930's 2 story @ 1200sqft) according to the agency that did our audit, so we are doing quite well compared to most.

One site I read ((broken link removed to http://www.epa.gov/iaq/homes/hip-ventilation.html)) mentions a 60 cfm rate of air exchange for a three bedroom house, or roughly 11 changes a day, as a recommended minimum.

These numbers aren't meant to come out for or against outside air for solid fuel appliances, but I hope they add some context to the small amounts of air that we are actually talking about.

 

[madrone]

I like fresh air. I don't mind if my stove pulls more in, because it heats it. But my wood is free. and it doesn't really get that cold here.

 

[TreeCo]

It's good to see the outside air supply myth finally being laid to rest!

 

[thechimneysweep]

By way of example, my house before renovations was rated at 8 air changes an hour ( 192 complete changes per day) and after air sealing and new windows, it dropped to 3.8 air changes per hour (91.2 per day).

Oconnor, I can't help but think you're mislocating a decimal point or two. The level of air change used internationally as the norm in terms of analyzing the success of various ventilation schemes is 0.3 air changes/hour, or 7 air changes per day.

You're in Canada, so let's take a look at the numbers from a 1989 Canadian survey of 200 homes across the country I found at (broken link removed)

In that survey, more than 70% of the homes surveyed evidenced an annual air leakage rate of less than 0.3 air changes/hour, or 7 air changes per day, which is right in line with the international norm.

You're describing your house, after air sealing and new windows, as having nearly 13 times that air leakage rate. If that is indeed the case, the additional 0.2 air changes/hour created by a woodstove does indeed look small.

If we move your decimal point over one place to .38 air changes/ hour, which seems a more reasonable level for a two story home built in the 1930's, the impact of the additional 0.2 air changes/ hour created by your woodstove looks far more significant: if fact, it constitutes an increase in hourly cold air infiltration of over 50%. In a typical home with an air leakage rate of less than 0.3 air changes/ hour, a woodstove installation with a 25 cfm outflow would constitute a 67% increase in cold air infiltration.

Check your numbers and let me know what you think.

 

[Todd]

It's good to see the outside air supply myth finally being laid to rest!

This debate will go on forever. I guess everyone will have to find out for themselves, both sides have good points. I noticed a huge difference when I hooked up outside air to my masonry fireplace which makes sense since it consumes vast amounts of air, but I took it off my stove downstairs, I couldn't control the input of oustide air to the stove even with a damper because it had an overhead run up the wall and through the sill plate. Cold air likes to travel down and it was being pushed into the stove too hard.

 

[bjkjoseph]

the reason for the oak is when there is multiple appliances pulling air out of your house,say you have a gas boiler and you have a dryer on and the stove on,the dryer and stove will pull the flue gases from the boiler into your house and you will not wake up because you would be dead from carbon monoxide.this is the main reason why out side air kits came into being.they have been using them for many,many years on big boilers.

 

[oconnor]

By way of example, my house before renovations was rated at 8 air changes an hour ( 192 complete changes per day) and after air sealing and new windows, it dropped to 3.8 air changes per hour (91.2 per day).

Oconnor, I can't help but think you're mislocating a decimal point or two. The level of air change used internationally as the norm in terms of analyzing the success of various ventilation schemes is 0.3 air changes/hour, or 7 air changes per day.

You're in Canada, so let's take a look at the numbers from a 1989 Canadian survey of 200 homes across the country I found at (broken link removed)

In that survey, more than 70% of the homes surveyed evidenced an annual air leakage rate of less than 0.3 air changes/hour, or 7 air changes per day, which is right in line with the international norm.

You're describing your house, after air sealing and new windows, as having nearly 13 times that air leakage rate. If that is indeed the case, the additional 0.2 air changes/hour created by a woodstove does indeed look small.

If we move your decimal point over one place to .38 air changes/ hour, which seems a more reasonable level for a two story home built in the 1930's, the impact of the additional 0.2 air changes/ hour created by your woodstove looks far more significant: if fact, it constitutes an increase in hourly cold air infiltration of over 50%. In a typical home with an air leakage rate of less than 0.3 air changes/ hour, a woodstove installation with a 25 cfm outflow would constitute a 67% increase in cold air infiltration.

Check your numbers and let me know what you think.

Tom

Thanks for the question

Took a look at my report, and I have the numbers right, but the context wrong - the AC/H rates are done during a 50 Pascal (Pa) depressurization test - so that will skew the numbers obviously. In an effort to translate 50 Pa tests to the numbers you correctly mention above, I did come across a report here - (broken link removed to http://www.pct.edu/wdce/wtc/pdf/Blower-Door-FINAL.pdf) - that essentially indicated that 5 ACH @ 50 Pa is approx the same as the .35 AC/H under natural conditions (they call it estimated natural infiltration rate (ENIR)). That ENIR of 0.35 would seem to be the number you are correctly noting above. Of note, the standard on the EPA site mentions 0.35 AC/H min, but not less than 15 CFM per person. In a 1000 sqft home, 0.35 AC/H is about right for 3 people - more people would require higher AC/H

So, in that context, the .2 ach from a stove is indeed significant in the overall scheme of air exchange. In my case, it looks like the extra .2 is needed, as I am resting below the 5 ACH @ 50Pa number, so likely below the recommended .35 ENIR number.

I hope that clarifies my numbers for you - I don't intend to try to clarify the OAK debate - to each their own - in my case, I don't have one, and couldn't likely install one very easily given my internal fireplace.