I had a Tamarack Ghost fan installed in a house I just had built. The specs say that it must have a minimum of 3.73 sq ft of net free area.
The builder did not install a gable vent. Just the ridge vent (and invisivent, soffit vents). The ridge vent it probably something like 15 feet long.
I am a little paranoid now that there may not be enough ventilation to keep the fan operating efficiently. Any thoughts on that?
The vinyl siding is already on. Does anyone know of a way to retrofit a gable vent if the consensus is that I need more ventilation area?
Bill
Replies
What you have with the fan off is a properly ventilated roof, one that slowly passes air from the soffit to the ridge.
When you turn the fan on, you pressurize your attic. The normal flow no longer applies. Instead the ridge and the soffits expel air like mad. If you don't have enough openings (I didn't do the math on your application), then your attic air will also escape back into the house though any available opening.
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Oh, good Lord, no. But I can give him two dollars and an assault rifle.
Thanx. My problem is that I don't know how to calculate whether I have enough opening given my 15 ft of ridge vent (and soffit vent which is probably a total of 20 ft due to the geometry of the roof (ridge is longer than soffit).
Measer the openings at the soffit, and figure out how many square inches there are. Do the same for the ridge, and see if they add up to be nearly what you need. TA DA!Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Oh, good Lord, no. But I can give him two dollars and an assault rifle.
Yes, do add up the areas of your openings and then multiply by the "net free flow area" as provided by the manufacturer of your soffit and the ridge vent.
The free flow area is less than the actual area of the ventilation products. And in real life those free flow characteristics diminish with time as dust and dirt oclude the opening holes or meshes.
A full flow gable ends would be a great idea and should be do-able as a retro. Make them plenty big or the whole house fan will not be able to do its job at full capacity.
.................Iron Helix
Ridge vent has typically about 18 square inches per foot. Invisivent claims 10 square inches per foot.
So the ridge vent is about 1.9 sq ft. If you have another 27 feet of soffit vent you have enough ventillation.
Gable vents are generally not a good idea as they short-circuit the passive ventillation of ridge vents, producing less balanced ventillation.
Thanx much. Using those specs, I pulled out my plans. Turns out I probably have closer to 25 ft of ridge vent. And probably about 22 ft of soffit (both sides combined).
So that tells me that the ridge yields 450 cu. in. and the soffit 220 cu. in. for a total of 670 cu. in. which equals 4.65 sq ft. The specs for the fan say to leave at least 4 sq ft. So maybe this is all OK.
What was bothering me was that there is a gap in the ceiling next to the fan which has yet to be sheetrocked and I felt considerable air blowing down through that. But maybe that is to be expected even with normal attic pressurization.
Bill
Yeah, the fan generates a significant amount of pressure, so you'd feel a good draft through any such opening, especially since it's venting to the space the fan is drawing from, creating a circular flow.
So convenient a thing it is to be a reasonable Creature, since it enables one to find or make a Reason for everything one has a mind to do. --Benjamin Franklin
A can of expanding foam will work wonders there to fix those gaps until it is rocked over again... check the outlets around the fan area too to see if they are blowing back.Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Oh, good Lord, no. But I can give him two dollars and an assault rifle.