Preventing backdrafting in the summer

[burnt03]

I’ve been burning for quite a few years, new problem cropped up as the weather got warmer and I stopped using the stove.

I installed a heat pump water heater in my basement that pulls air from inside the home and exhausts it outside. It changed the burning characteristics a little bit but still worked OK. As I stopped burning though, it’s pulling air down the chimney and I get the smoky/creosote smell in the basement.

Any ideas on how to prevent that? Bag of insulation at the top of the chimney to slow air flow? Plate of baking Soda In the firebox? Can’t really install an outside air kit as the crawl space under the stove is inaccessible and the wall directly behind the stove is the cinder block chimney.

Thanks

EDIT: Regency F2400

 

[begreen]

Is the stove also in the basement? The problem should be reduced if a basement window can be cracked open an inch during the summer. Or, disconnect the stove for the summer and cap the stovepipe at the stove's flue collar connection or cap the chimney thimble.