Unvented crawl space mechanical ventilation question
I am building a diy ICF house on a crawlspace (ICF from footer to roofline) in Louisville, KY Climate Zone 4A. I planned on having an unvented crawl space and have a question in regards to the energy efficiency of what I am thinking. I was hoping to save on the HVAC installation cost by installing a 36k BTU 4 zone mini split diy mini split and using supplemental gas or electric heat when it gets to cold outside for the heat pumps. The house will be roughly 1750 sq ft.
Code book reads like so on unvented crawl spaces
One of the following is provided for the under-floor space:
I was planning on option 2.1 installing a bathroom vent fan in the sealed crawlspace venting to outside and a one transfer grille in the floor to allow air flow from the living space. I see per code I would only need 35CFM (1750/50=35CFM) on this vent fan but was planning on a 50CFM unit or so. My question is this option for an unvented crawl seems kind of wasteful and would negate the effects of a air tight well insulated house if I am constantly blowing out conditioned air compared to the other two options. However If I use the other two options I will need to either buy another mini split for the crawlspace or hire an HVAC contractor to run duct work and use a normal ducted system. What do you all think is the cheapest / most energy efficient option?
Last question, am I reading the code book wrong all together and it is not saying to vent air outdoors from the crawl space, but option 2.1 is actually talking about having an exhaust fan pull air from the crawl space and venting to the main floor with a transfer grille to provide circulation or vice versa?
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