A 13x13 for a furnace??? Wow! must be a real monster! Talk about oversized flues...

There is no concensus on staggering of masonry flues. The tiles should project 2-4" above the crown wash. Most factory built fireplaces state how to stagger multiple fireplace chimneys within the same chase but the only one I'm aware of that addresses heater flue proximity is HHT( Heatilator, Heat&Glo, Quadrafire). Generally, the heater flue is staggered higher to disperse its nasty fumes without rotting the nearby metal and not recirculate fumes down the fireplace at standby. BTW, I got them to address this issue in their manuals.

Seems like every time I remove one of those OD Funk tops, there are stink bugs packed into those folds in the corners.

Bob

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disgusted with some people on this forum. Out of here!