[Greenbuilding] Back to Rumford fireplaces, tight homes & backdrafting

[Tom St. Louis]

Builder has installed Rumfords in two SIPs homes. The homes are so tight 
that when the kitchen fan is turned on, the chimney backdrafts (even with 
the combustion air supply open at the side of the fire box), this gets worse 
as more fans and the clothes dryer are turned on. Even the 'supposed' sealed 
combustion Rinnai on-demand water heaters backdrafted. Oh dear!

More make-air sources are going to be added or maybe a larger single source 
possibly behind the kitchen stove. Looking at adding sealed glass doors to 
the Rumfords to add extra insurance to prevent backdrafting.

Will a wood fired Rumford firplace work having air-tight sealing 
ceramic-glass or other high temp glass doors with outside combustion air 
source? Can they be converted to gas log Rumfords with airtight sealed doors 
and still work?

Big reminder for everyone.........
Add up all the maximum CFM capacities of all exhaust air fans and appliances 
in your buildings while still at design stage, then plan and specify make-up 
air source(s) equal to worst case for air being sucked out. Must have 
incoming make-up air equal to what is being exhausted.

Add an adjustable barometric type or electronically controlled damper to 
allow needed make-up air to prevent backdrafting or sucking air through 
cracks in the building envelope. Some homes with those modern stainless 
steel 700 to 1500 cfm kitchen fans or down draft stove fans would require a 
fan to bring make-up air in.

Tom