Chestnuts and frost-free days

I just asked Badgersett Research, but it's worth asking for actual field experience here. How few frost days can I get away with and get chestnuts to finish?
We are in Zone 5/6, but maybe only 125 frost free days, although my squash made it 150 days this year.
I suspect that isn't enough, even if they survived the 7.5 pH soil.

Anyone growing chestnuts in the intermountain west? Chinese, American or hybrid? Yields?

Chestnut can grow to zone 4 bordering zone 3.
Zone 4 is about 120days aka 4*30. So you should be ok esp if you get a zone 4 hardy cultivar.
Another thing to look up is your growing degree day and total hours of sunshine.
120day with a avg of 10hr of sun is going to beat 200day with a avg of 4 hours of sunlight.

Can you really deduce frost free days from the zone? I thought it was only referencing the average annual minimum temperature. We are likely on the edge of 5/6 (severe valley microclimate means the maps aren't precise enough) but our frost free days are way fewer than a New England 5/6. In other words, a late season apple like Granny Smith might survive our winter just fine, but would never develop mature fruit. We need late flowering/early fruiting (nutting?) varieties in everything else, stands to reason the same would be true for nut trees.

Edited to add
WRCC lists Loa (16 miles and 200' elevation upstream) at 2496 corn growing degree days and Capitol Reef National Park (9 miles and 1500' downstream) at 3840. But I can grow tomatoes here, they can't in Loa. There isn't enough granularity in the historic data. And is a corn degree day relevant?

On the east coast, zone roughly = frost free month,
but on the west coast it is different which is why the west coast uses the sunset zone.
A WA/BC zone 8 and a TX zone 8 vs a GA zone 8 are all totally difference beast.

I would still give a zone 4 hardy chestnut a try in your UT zone 5/6
Here is another chestnut vendor you could try out http://www.sln.potsdam.ny.us/2013lcataloglores2.pdf

I would say from talking with other nut growers in the Eastern US, that there is a big difference between Zone 5 Pennsylvania and Zone 5 Colorado. The biggest difference, I think, is nighttime low temps during the frost-free period. Here in Colorado, Zone 5 nights during the warmest part of summer are never going to get much above 60 degrees. Wheras in the Eastern US, they get nice warm nights through the summer season that really makes plants grow. It's all a function of altitude and humidity, one of which we have and the other we dont.

I dont know of anyone who has successfully grown chestnuts in the interior Mountian West. Sure would love to find that guy, and find out what it takes to make it work though.

I'm in Klamath Falls, Oregon, which is listed as zone 6, but we hit -13 this week, so maybe it's more like zone 5. We average 106-120 frost free days, depending on which source you trust. I'm new to the area this August, but according to the locals there was a hard frost the third week of June this year, so there were almost no apples or other standard fruit in town this year (but native Klamath plums, elderberries, bitter/choke cherries, ribes species, etc. all had plenty of fruit on them).
I found a chestnut in a public park here. I don't know what species/varietal it is, but it is definitely a true chestnut, medium sized single-trunk tree. It opened it's burrs and dropped nuts at least a month after the first frost, sometime in October; however, the nuts were empty. From my understanding a chestnut won't set seed without another individual for pollination, and this one is all by itself, so that is likely the cause, though I can't conclusively state such.
To echo Adam, the large diurnal temperature swing in the arid West is fairly problematic for many species (in summer the average swing is 35 degrees here), but the chestnut I'm referring to is a fairly large healthy tree. I should state that it is within a few hundred yards of a large lake, which might moderate the climate a bit, and it is in a public park next to grass, so it gets irrigation. As to soil, I haven't dug in that location, but based on the county soil survey, it is a loam made from sanstone, breccia, diatomite, and basalt, though I don't know the pH. The land is slightly sloping to the north, but it isn't shaded at all, being in a open grassy area, except maybe in mid winter the sun may dip a bit below the hills to the south of it. We get just shy of 2000 degree heating days here (warm sunny summers). Just trying to give as much info as I can hoping some of it may be of use to someone. My thinking is that chestnuts could work here, based on all this, but until I see full, tasty chestnuts falling from a tree here, I can't be sure.

I don't know about the west, I live here in upstate NY, solid zone 5. I live in a narrow valley with serious early and late frosts every year. I have been growing hybrid chestnuts here from seed collected nearby in an equally frosty valley. The trees are hybrids, mostly consisting of chinese, american, and japanese genes. They ripen earlier than typical asian chestnuts. They have been bearing regular crops of chestnuts for the past 30 years here, typically ripening around the end of september. It takes a true killing frost to destroy the nuts.
I do sell seedlings through my nursery. Check out our website if you'd like to know more about the genetics of our trees www.twisted-tree.net

I also agree that not all areas in a zone are the same. Our valley has about 30 less days than the nearby finger lakes region.

I forgot to post that I got back an answer from Badgersett in the form of a question: "It sounds like the most limiting factor is going to measureable amount of moist. How much rain do you get annually?"
They didn't say we didn't have enough days to maturity. Moisture I can control to some degree with our irrigation, at least until the trees get established.

What's the worst that can happen? I spend some money. I grow some trees that don't fruit but make shade, leaf litter and we learn something. Maybe we get chestnut blossom honey. Or maybe I cut them down, if I live long enough to try something new and I have a better idea. We're going to give it a go.

I think that 110 days is more than enough for the chestnut. go ahead and give it a shot, maybe in 10 years when someone else comes here asking you will be able to give them a better answer.