Using more pellets when outside temp is warmer???

My mother has a Harman pellet stove (P65, I think). It's never heated very well. We are currently having a cold spell and she is reporting that she is using less pellets now than when it was warmer. That doesn't make much sense to me, but I'm not a pellet stove user (I use a wood stove). I'm wondering if the stove could have a problem like some Blaze King wood stoves have had. Blaze Kings have a thermostatic control (bimetallic spring/coil) that controls the burn rate of the stove. Some Blaze Kings have been found to have the bimetallic spring/coil wound in the wrong direction (so that it coils and uncoils incorrectly/backwards), thereby setting the burn rate incorrectly (high when you actually want low temps and low when you want high temps). I was wondering if pellet stoves might use a similar device and, if so, has anyone heard of them doing the opposite of what is called for by the temps? Or could someone offer a suggestion as to why she would be using less pellets in a cold snap and more when it is warmer out? Thanks.

There is a long list of possibilities you can start with wind load and air infiltration for just two.

it's possible it could be the stove temp probe...
i'd suggest trying to find out if its in room temp or stove temp mode. see sticky at the top.

It's in room temp mode.

Even in room temperature mode the probe placement can be such it is getting hit by lower temperatures when the outside is at a higher temperature than it was when the stove was burning fewer pellets.

Another to consider is since the heat that gets into the house is affected by how clean the stove is as the time increases from the last cleaning there will be less heat produced for a given pound of pellets burned, yes this implies that even at the same outside and inside temperature settings the stove will burn more pellets as each day goes by.

This could be far fetched but I will say it anyway

If she has a well insulated house and an OAK installed, the colder air could be helping.

The colder more oxygen dense air combusts much better than warmer less oxygen dense air does. With good insulation in the house the combustion advantage of the cold air may be outweighing the disadvantages of the cold temps.

Again she would need good insulation and an OAK installed for this to be anywhere near a possiblity. Just a thought!

Nope. No OAK and insulation, while way better than my house, is not up to modern standards.

She cleans her stove religiously and thoroughly every week. She's compulsive about such things. I think the placement of her probe is OK, I read the sticky and she's not violating any of the big gotchas.

Did anything around the house change besides the temperature? Things like snow and ice on the roof or against the house's foundation?

Did she go in and out of the house more when the temperature went up outside?

Were the winds the same in terms of speed and direction.

Remember I did mention that the list is a long one are there soffit, ridge, or end vents for the attic?

Did the air pressure change?

Was it clear on the cold days and cloudy on the warm days = solar heat gain through window glass and from walls and roofs.

I wish this would happen to me so I could get some first hand experience. This is twice I have heard this now in two weeks.

We had a house that had wall of windows in two rooms that picked up a lot of sun on cold winter days and those rooms were warmer on a cold clear day than on a cloudy day. One of those rooms had windows on both of the two walls.

I did say the list was long and you were the one who provided a link to course material dealing with heat loss.

Lol. Not complaining. Curious!

Does Harman make a p65?

I have a similar issue when a warmer wind blows from the southeast . I've got a lot of doors and windows on those exposures

I just had a thought. The venting becoming colder could reduced natural draft, more heat output from the stove. The effect would be very dependent on the venting configuration. Longer exposed runs more susceptible.