COLD AIR EXCHANGE EXPLANATION???

[Tonyray]

Simple OAK setup from inside to outside.
Horizonal Air inlet is Behind the outside bottom cap.

 

[doghouse]

All incoming air is warmed by the exhaust so no reduction of efficiency on very cold nights.

I do not see how this is possible.

 

[HP52NOVA]

I do not see how this is possible.

Let me try to explain as best I can (I am not an expert): It's a feature of the direct vent solution - as the hot exhust is going up thru the 4inch inner pipe, the fresh air is pulled down using the same pipe as it has an external 1inch evelope. The cold air in the envelope is then heated by the inner exhust pipe and is warm when it hits the combustion chamber. Since you are using existing heat from the exhust to heat the air intake and the combustion air is warm vs. cold, you get better efficancy as a result (no cold air in the stove). This concept had been used for years with wood stoves, now also with pellets. I had a regular OAK and converted to this, and I can report visible improvement. I love this pipe!

 

[doghouse]

Let me try to explain as best I can (I am not an expert): It's a feature of the direct vent solution - as the hot exhust is going up thru the 4inch inner pipe, the fresh air is pulled down using the same pipe as it has an external 1inch evelope. The cold air in the envelope is then heated by the inner exhust pipe and is warm when it hits the combustion chamber. Since you are using existing heat from the exhust to heat the air intake and the combustion air is warm vs. cold, you get better efficancy as a result (no cold air in the stove). This concept had been used for years with wood stoves, now also with pellets. I had a regular OAK and converted to this, and I can report visible improvement. I love this pipe!

I know how it works, it's the physics I don't buy. 1300 degree fire affected by air 60 degrees less cold?

 

[Wilbur Feral]

I know how it works, it's the physics I don't buy. 1300 degree fire affected by air 60 degrees less cold?

Exactly.

 

[HP52NOVA]

I know how it works, it's the physics I don't buy. 1300 degree fire affected by air 60 degrees less cold?

I am in no way a physicist, but here is what I think: the key to any OAK is to provide an external source of oxygen to a fire, if the incoming air is warm instead of cold you will spend less energy heating it. It may not be a large difference for a 1300 degree fire, but frozen air would still take some extra BTU's to heat, while warm air has as much oxygen but takes less BTU's away from the fire. As you are re-using the heat you are already sending (waisting) up the flue, you recalim some of that lost energy and heat your air "for free", hence improve your efficiency. This sounds logical to me. Maybe someone here knows the science better and can chime in with a better or alternate theory.

Keep in mind that these pipes are so very new to pellet burners and there is little community experience with them. I am the only person i know to use this configuration (Harman 52i insert with vertical Ventis DV), as I agreed to be the first install (yes, willingly ). Feel free to ask any questions, I will be happy to share details.

As I see it, many dealers don't want to install OAK's because it complicates the install and creates liability with cutting extra holes into customers homes, so if it works without one, why bother? So here is a solution to make two holes in one, class A chimney, etc. I only have it running for two weeks, but I would recommend it for any new install (or re-install). It makes my old Selkirk pipe look like an outdated piece of metal.

 

[checkthisout]

I know how it works, it's the physics I don't buy. 1300 degree fire affected by air 60 degrees less cold?

The fire must heat this air. Any drop in the incoming air temp results in lower temperature air being passed across the heat exchanging surfaces of the stove for the given amount of fuel burned.

Regardless, the OAK ensures that you're not sucking already heated interior air outside through the vent.

 

[checkthisout]

this thread already belongs to arm chair physicists and nascar aficionados...

That's a pretty harsh comment to make. What gives?

 

[Deezl Smoke]

I am in no way a physicist, but here is what I think: the key to any OAK is to provide an external source of oxygen to a fire, if the incoming air is warm instead of cold you will spend less energy heating it. It may not be a large difference for a 1300 degree fire, but frozen air would still take some extra BTU's to heat, while warm air has as much oxygen but takes less BTU's away from the fire. As you are re-using the heat you are already sending (waisting) up the flue, you recalim some of that lost energy and heat your air "for free", hence improve your efficiency. This sounds logical to me. Maybe someone here knows the science better and can chime in with a better or alternate theory.

Keep in mind that these pipes are so very new to pellet burners and there is little community experience with them. I am the only person i know to use this configuration (Harman 52i insert with vertical Ventis DV), as I agreed to be the first install (yes, willingly ). Feel free to ask any questions, I will be happy to share details.

As I see it, many dealers don't want to install OAK's because it complicates the install and creates liability with cutting extra holes into customers homes, so if it works without one, why bother? So here is a solution to make two holes in one, class A chimney, etc. I only have it running for two weeks, but I would recommend it for any new install (or re-install). It makes my old Selkirk pipe look like an outdated piece of metal.

Actually no, warm air does not have quite as much oxygen. Google can help with this. But I think it is Charles law of gases(??) that explains the effect of temperature on gases. Basically it is the reason heat rises, or goes up and cold goes down. Cold air is of higher density as more molecules fit in a given area. When heated, the molecules expand. Large molecules means less of them in the same area size. Less dense air is lighter, and more buoyant. So heavier, more dense air can move in under it and push the lighter air upward. (I am in no way a physicist) But google can verify this easy enough.

That said, rocket stoves preheat the incoming air for the same reason mentioned in this thread, the colder the incoming air, the less heat will come from the heater.

I'm not so sure we are giving the OP the right info now that I re-read the opening statement. There is a difference between an air exchanger and a outside air intake kit. (OAK) The exchanger would include outside air, but the outside air would be warmed as it passes thru the exchanger on it's way to the combustion intake.

 

[checkthisout]

My plan was to draw it from the attic. Still might, but everything is working fine with nothing attached to the stove inlet so far.

You don't want to draw from the attic. If for some reason there was flow reversion you could possibly get sparks or smoke up there.

 

[checkthisout]

You'd prefer drawing -20 degree air into your house in the form of drafts to compensate for the vacuum created by your stove?

This is what the couple holdouts against OAKS believe. They believe the reduction in firebox temperature caused by not admitting room-temp air into the firebox from the house is the same difference as letting combustion make-up air in through the normal cracks and crevices in the house.

 

[Deezl Smoke]

You don't want to draw from the attic. If for some reason there was flow reversion you could possibly get sparks or smoke up there.

That's a very good point. With the combustion air tube as high as the exhaust pipe, in some circumstance, it may back flow.

 

[doghouse]

Alright.

 

[Wilbur Feral]

And so, exactly how many angels are able to dance on the head of a pin?

 

[Tonyray]

Actually no, warm air does not have quite as much oxygen. Google can help with this. But I think it is Charles law of gases(??) that explains the effect of temperature on gases. Basically it is the reason heat rises, or goes up and cold goes down. Cold air is of higher density as more molecules fit in a given area. When heated, the molecules expand. Large molecules means less of them in the same area size. Less dense air is lighter, and more buoyant. So heavier, more dense air can move in under it and push the lighter air upward. (I am in no way a physicist) But google can verify this easy enough.

That said, rocket stoves preheat the incoming air for the same reason mentioned in this thread, the colder the incoming air, the less heat will come from the heater.

I'm not so sure we are giving the OP the right info now that I re-read the opening statement. There is a difference between an air exchanger and a outside air intake kit. (OAK) The exchanger would include outside air, but the outside air would be warmed as it passes thru the exchanger on it's way to the combustion intake.

Not an expert here also but our 1st year with a pellet stove[without an Oak], We always noticed when we sat on the floor with our dogs there was Always a cold draft current crawling along the floor.. Easy enough since we have an 90 yr old 2 story house...
after reading about this very subject, we had the OAK installed and floor draft problem was eliminated 2 seasons ago.. As stated in this thread, new or fresh air has to come from somewhere In The house if not piped directly into the stove.

 

[GeHmTS]

Guys, this is all thermo 101. Air has a certain heat capacity and is much easier to heat than less say water or moisture. So your heat is more limited by moisture rather than cold air. So from my perspective as a physicist, it would really depend on how much moisture you are carrying from the outside air into the stove, NOT how cold the air is itself. Dry air heats up pretty quickly, moist air less so.

 

[Edsson]

A simple question. With my pellet stove on the first floor,what is wrong with pulling 55-60 degree air from a pipe through the floor into the basement? With movement in the house and people coming and going opening doors(inside or outside) and what have you, I find it hard to believe you are going to pull enough negative pressure in your entire house to draw that much air from outside. With a 2000 sq. ft. house, and another 800 sq. ft. basement that is a lot of cubic feet of air to pull down much past 760 mmHg. If that's true I would rather draw in air from the outside in the basement where it can equalize the temperature with the rest of the basement air, than drill a hole in the side of my house to get freezing cold make-up air. I burned wood for 28 years in the basement and now burning pellets for the first year on the first floor of a 2 story house. I love the pellet stove, and cutting, splitting and hauling all those bags from my basement are sooo much easier than hauling 5 cords of wood from outside. I use this forum for everyone's incredible knowledge, I just don't want to be drilling holes where I don't need to.

 

[Wilbur Feral]

Believe whatever you want. Math and physics are constant. Beliefs are what seem to vary. Sigh... Humans...

 

[doghouse]

What's the argument again? OAKs or Temps?

 

[TimfromMA]

There is no argument. Install OAK or don't. You are the one who has to live there.

 

[doghouse]

Hmm. My posts were never against the OAK. Oh well.