Downdraft smell worse with EPA insert

In February I replaced my smoke dragon Gold-Marc insert with a Lopi Freedom. Due to the mild Winter I really haven't been able to appreciate my investment, and now I have to deal with a downside. The regular Spring down-draft sooty smell is much, much worse. I never imagined that the old unit with its sliding damper and holes in the door would seal better than an "airtight" stove.

I made a point of burning a hot last fire (but not as hot as the Gold-Marc would have been), I plugged the adapter above the bypass with rags, but the smell is there every day when I come home. Previously I would only get the smell on thundery days with rapid weather changes. I didn't clean the liner, but there were at most 10 fires in the new liner, all but one with well-seasoned wood.

Is this to be expected with an EPA unit? Is there any way I can block the air intake? Would blocking the liner at the top help (are there proper plugs available)?

TE

Blocking the liner at the top should solve the problem. Just leave a note written in LARGE writing reminding yourself that it's blocked, or your smoke smell is going to be much worse

Note went in the firebox when I plugged the bottom, but thanks.

New EPA stoves are NOT airtight. Thats why they are EPA approved. Most have a Primary air control (you control) and then Secondary air (tubes / uncontrolled / opening somewhere on insert) and also dog-house air (hole or holes in the bottom front of stove/ also another opening thats uncontrolled and wide open).

So there is at least 1 hole ( possibly 2 ) that is not blocked.

There is a large misconception that new stoves are airtight.... Its the exact opposite. Some old stoves are built that way. Only air source was controlled by the user and could be shut completely down (aka - Smoke Dragon).

I would try an clean it. Even if it was only a few fires.

The smell is more than likely creosote. You said one fire was less than desirable wood. How long did your other wood season? What species?
They sell "balloons" to plug the flue. But a bag or plastic up top will do the same thing...

I knew it wasn't "airtight", that's why I used quotes. I was surprised that it was less airtight than my old insert which had at least two 1/4"x1" holes in the door plates. I'll give at a clean anyway, and block the top too. Those few fires were with several years seasoned wood. One fire did include some one year seasoned oak, just to see, so I suppose now I see...

TE

You are on the right track by blocking the pipe. I take old clothing and stuff it in a trash bag and then squeeze it into the pipe. You may have to leave a window cracked when running the air conditioner.

I have never noticed a smell on any of the five stoves I have had installed. One of which was a Pre-EPA stove. I wonder what the difference is between your situation and mine?

So many things could influence the smell, or its cause. Location of chimney relative to sunshine, air-tightedness of house, prevailing wind direction. The basic reason is the stack effect in any house causes lower pressure downstairs, which will draw air down a cool chimney. Probably only noticeable this time of year because there is neither heating or cooling running in the house, so very little air movement, and obviously the stove is not running. My shaded chimney makes this worse, as do my efforts to air seal the house which means there are less other ways for air to enter.
TE

I get a really mild smell right once in a while around this time of year, only on rainy or muggy mornings. Barely noticable until you come into the kitchen where our main stove resides. It usually goes away after a week or two. I am burning really well-seasoned wood and I don't get much creosote to begin with.

this dude took the words right outa my mouth! great post and well said... air tite pre-epa stoves FTW! haha. anyways, i think cleaning unit and flue is your first line of defense here Dexter is absolutely right that this horrid smell on those musty damp days is creosote build up (most likely in the flue/chimney not your brand new stove/insert), then second line of defense is to seal that chimney/flue up during the off season when you have no draft going out of the home from the fire you probably always have burning when its wet and yuckie outside (thats why you dont notice this smell so much during the burning season).

I knew the moment I used the word "airtight", that it would be the focus of attention. I know EPA Stoves are not airtight, that's why I asked about any way to block the air intake. I also know that my old insert was not airtight because there were holes in the door frame. What I don't understand is why the smell is much worse. With the old insert, the chimney didn't even get swept each year, and even on the "dirty" years, the smell wasn't as bad as with this new insert. As for seasoned wood, the old insert could handle anything, so that's what it was fed - anything, I knew the new insert wouldn't and made sure to give it well seasoned wood, except for a few 1-year oak splits just to see how it would do. The existing chimney was cleaned very well by the liner installer, I was actually frustrated at how long he was taking (couldn't wait for fire up).

TE

I cleaned the liner, got only a few tablespoons of brown powder, but the smell is immediately better. That's after several strong thunderstorms, which usually make it worse. I still don't understand why the new insert would smell more after just a few fires than the old slammer did after two whole winters, but that's how it is.
Theories:
One more reason to only burn very well-seasoned wood?
Narrower liner means higher downdraft velocity, picks up more smell?
Insulated liner increases downdraft by reducing solar warming of flue?
Removal of flagstone cover changed airflow making downdraft worse?
Slammer ran much hotter?
Experimenting with overnight burns caused increased creosote?
Burned much more Hickory this year than usual, does this smell worse?

Anyway, maybe I'll never know. Thanks to everyone for their advice.

TE

As I mentioned above, some air-tightening over the last year, but nothing huge so I'd be very happy if it had an effect this noticeable...
Once A/C weather is here, the smell seems to go away, probably since there is more air movement again, and usually comes back again in fall when there is no heat or A/C. Don't get me wrong, this is not a strong smell, but noticeable when I come home most days, usually disappears once everybody has been running in and out.

TE

As I understand it, there is an inherent slight negative pressure in the lower level of all buildings due to the stack effect. I understand exactly what is causing the smell, but I am curious to why it might be worse now, and if anyone else has experienced the same. It seems odd to me that so many people seem to have never noticed this phenomenon at all.

TE

My 30-NC is in my Basement... I am likely gonna plug the Flue this week, but I have a fair amount of downdraft coming down my flue. When I open the door, you can feel the air coming down off the top of the ceramic boards..

I have 18' of Class A outside and then 3 ft of Horizontal (double wall) and 4 ft vert (double) coming into stove. So about 25 ft of total length. I notice the air, but no smell.

(I am plugging to help seal the house/ also to keep any humid air that may want to ride down the flue and rust the interior of the stove)