We are trying to replace a steel freestanding fireplace (very decorative, not warm or efficient) with a Kent woodburning stove. The old fireplace had 7" single wall pipe going into the chimney. The new stove has 6" inch pipe. (Will also need an elbow to connect the new stove to the existing chimney.) The local fireplace store tells me there's no such thing as a "decreaser" but I see them available online. Would be grateful for suggestions and advice ---