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Hood vent path using two duct sizes and venting down

3 years ago

I made a huge oversight in planning my kitchen and first floor renovation and need help with a solution. I am the designer, project manager AND am using the contracting company that I OWN to preform the work. I only have myself to blame and feel like a complete idiot for making such a dumb and obvious mistake so please go easy on me.

Some relevant info to consider:

- Plumbing, electrical, HVAC, drywall, LVLs and paint are all done based on current kitchen design and appliance placement. Including plumbing and placement of pot filler for range.

- All appliances are purchased and paid for EXCEPT hood vent insert

- Kitchen design is finalized and cabinets are ordered

- forgot to let my sub know that instead of two wall ovens and a 30' cooktop (original plan) I was doing a 48' slide in pro-style range until it was too late to find a new duct path.

- right now there is a 4" duct soft rough in from vent location down to crawl space

Icing one the cake?! My THREE very young children, my husband and I are living upstairs, without a kitchen, during the renovation. Time is of an essence!

Ok, now that you have some idea of job status and possible financial and time repercussions, here is the problem.

Unless we move both the warm and cold air returns, upstairs plumbing, or all of the various kitchen plumbing lines, the only clear path for the vent duct work is in-between the air returns and a water line pipe. There is a horizontal pipe blocking the path up and out and a stud in the other direction. HVAC is probably my weakest area of construction, but I do know that with a range that size i will need a hood vent with at least a 900-1100 CFM blower which ideally should have 10"-12" ducts. There is plenty of room in the crawl space for a 10"-12" duct but only 4", MAX 5.5" from vent to hole to crawl space in-between air returns and pipe. From the vent, to the 90degree and and out the back of the house will be roughly 20'. Two issues/questions off the top of my head:

1. Consequences of going from a 10" duct from vent to a 4" duct then back to a 10" duct once in crawl space (if that's even possible!?).

2. Can I even vent down and out through crawl space. Again, HVAC is not my strong suit but i thought that was a no no.

So, now that you know the extent of mistake, what are your thoughts on the 2 issues that came to my mind and are there any more? Do you have any suggestions or creative solutions? What would you do if it was your house and your money? and my pride ;)

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