.5 micron filter question

[Bit_Fiddler]

I live a bit south of Minneapolis, with a very well insulated standalone 28x25 shop building on an insulated slab.  I would guess that my average run times on my cyclone is 20-30 minutes - sometimes more, sometime less.  Definitely more than 5-10 minutes at a crack.   I can tell you from direct experience venting outside will make your heat source run more frequently, crowding constantly depending on outdoor temps.   I often spray lacquer for a finish on my projects and to help reduce the fumes in the shop, I open windows across the shop from each other to vent fumes.   I place a cheap 20" box fan in one of the windows (depending on wind direction) to aid the process.   Whether is 30 degrees or -10 degrees, the furnace (sealed combustion) runs significantly more often.   The colder it is outside, the more often the furnace runs - it is an intuitively obvious observation - that is easily repeatable.   The shop doesn't *feel* much different, but that furnace runs more, without a doubt.  A cheap box fan is going to push dramatically less air though a window screen than a dust collector directly venting outside - so the impact would only be greater with a dust collector exhausting outside.  I thought long and hard about outside venting after building my shop, even framed a spot for the vent when building the shop, but the experience with 2 open windows and a box fan made it an easy decision not to vent outside.  I'm still thinking about some sort of a filter bypass that would allow me to vent outside in the late spring/summer/early fall when the temps are moderate, but have not discovered an air tight bypass that would not leak dust like crazy when filtering.

I'm honestly not trying to throw stones, and more moderate climates are clearly less impacted, but I am honestly curious about some of these questions....
I have no doubt that the basement shops have more mass to hold heat, but I think that is less of a concern in northern climes where frost can penetrate 4-6 feet (or more) down.  A bigger concern in my mind is where does your make-up air come from when you are venting 1000 or 1500 CFM outside?  A 10x12x8 room is a little less than 1000 cubic feet - pumped out every minute. Do you have an open window in the shop or is it drawing that make-up air from the rest of the house?  If you don't have an open window in the house or shop for make-up air, where is it coming from?   Unless you have sealed combustion HVAC and hot water heaters with outdoor combustion air sources, it is almost certainly reversing the flow in your chimneys and possibly introducing flue gasses to the interior environment.   It's a very similar situation to an energy audit where they install a door fan to check for air leaks - make-up air has to come from someplace and chimneys are a prime source when there is negative relative pressure inside the building induced by a fan.  That is why the furnace and gas hot water heaters are turned off during the audit - I asked.

Dave

[jteneyck]

Dave, I have another window in my shop that I open for make up air.  My boiler and water heater both sit in an open alcove in my shop, draw combustion air from my shop, and vent to a standard chimney.  Sealed combustion would clearly be better but this is what I have and I've had 0 problems with it since I started venting my DC outside.  I was very concerned about it being a problem and was extra cautious to check the airflow when both the DC and boiler or hot water heater are running.  I first checked w/o the boiler running and it was fine, so then I checked it again after turning the boiler on, and it's still fine.  

Of course your furnace will run in the Winter when your DC is venting outside, and it gets pretty cold here in WNY for many months.  Until you actually measure how much more fuel it takes to bring your shop back up to temp. you won't know how much it costs.  


John

[Bit_Fiddler]

Dave, I have another window in my shop that I open for make up air.  My boiler and water heater both sit in an open alcove in my shop, draw combustion air from my shop, and vent to a standard chimney.  Sealed combustion would clearly be better but this is what I have and I've had 0 problems with it since I started venting my DC outside.  I was very concerned about it being a problem and was extra cautious to check the airflow when both the DC and boiler or hot water heater are running.  I first checked w/o the boiler running and it was fine, so then I checked it again after turning the boiler on, and it's still fine.  

Of course your furnace will run in the Winter when your DC is venting outside, and it gets pretty cold here in WNY for many months.  Until you actually measure how much more fuel it takes to bring your shop back up to temp. you won't know how much it costs.  


John

I don't feel like I really need to calculate it - It's a big gas furnace and it runs often enough (down to 10 minutes between cycles when really cold and the windows open) to know that it would have more impact on the bill than I care to pay for.  With everything buttoned up, it runs 1 time and hour to 1 time every couple of hours.  Why go to the expense of the extra insulation that I did if I'm just blowing all of the warm air out the window?  Since the furnace would be running very frequently anyway, why insulate?   The filters have been working just fine and not caused me any reason to change the design.   The only reason it's a consideration during the moderate weather is where the dust collector would act like a whole house fan and change out all shop air several times an hour reducing the use of AC.  To each their own, I guess.

Dave

[jteneyck]

I don't feel like I really need to calculate it - It's a big gas furnace and it runs often enough (down to 10 minutes between cycles when really cold and the windows open) to know that it would have more impact on the bill than I care to pay for.  With everything buttoned up, it runs 1 time and hour to 1 time every couple of hours.  Why go to the expense of the extra insulation that I did if I'm just blowing all of the warm air out the window?  Since the furnace would be running very frequently anyway, why insulate?   The filters have been working just fine and not caused me any reason to change the design.   The only reason it's a consideration during the moderate weather is where the dust collector would act like a whole house fan and change out all shop air several times an hour reducing the use of AC.  To each their own, I guess.

Dave

I wasn't suggesting you change what you are doing.  I was addressing the questions you asked regarding make-up air and safety so that the OP has a more complete picture of what has worked for me, as he is still deciding which way to go.  

John