My under quilt(UQ) is rated to 20F and even though I'm a warm sleeper I don't overheat in it. But one advantage I have is, I use a Mount Washington 3 convertible from Jacks-R-Better. It separates into 2 pieces so it goes from a full length UQ, in winter, to a 2/3's length, in summer. With just a piece of good velcro and a draw cord worth of of weight, it becomes almost a 4-seasons UQ. I used it below 0F, with a pad, without getting cold yet. This nice piece of kit enables me to get away with only having to buy one UQ.
Everyone varies in thier sleeping "temperature" as others have said. I generally use a 3/4, 40 degree phoenix (known as the "Summer Phoenix" until recently), with no overstuff as my go-to quilt. I've taken it to 27 degrees, and slept comfortably. I would say 25 degrees is it's limit.
I sleep warm, so I can generally take temperature ratings about 10 - 15 degrees lower than stated.
Mike, Backcountry Mentor
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Tried the UQ this morning. It was 22* here. I used a 30* sleeping bag as a TQ just to hang for a while and get a feel for things. I cinched up both ends of the UQ and jumped in. First I was right I"m a little wide for the UQ at the shoulders but the outer part of my shoulders didn't get cold. Between my shoulder blades was a different story I seemed to get a little bit of a cold spot right between my shoulder blades and any time I fidgeted a little bit the cold spot would hit then slowly go away so I'm not sure if it was because I didn't have it cinched enough or to much. Any feedback?
Other then the cold spot between the shoulders I was as snug as a bug in a rug.
I had a couple of cold spots when I was sorting mine out too. I thought about putting more bungee on the loops along the sides. I talked to Adam via phone. He said to take out about 3" of the bungee by tying a square knot about 3" up from the first one on the end. Then re-hang it over the gathered ends. This will draw the UQ up tighter on your backside. Repeat as needed.
The second thing he said (which really helped) was to find the loop between the shock cords on one end and to attach it with a bungee to the gathered end. He said that by attaching these two loops at each end, it will pull up the middle of the UQ along it's length to match the sag of the hammock.
Let us know how it's going...