using thermarest folding pad beneath.
down sleeping bag "rated 0 F".
sleep clothed with beanie and bag mummied up.
jacket layed on top of my face

sale rep said they changed the rating system to a third party standardized rating system now. My bag might hit 15-25 on the new standard my guess.

should i upgrade my bag, upgrade to a warmer sleep pad, or 2 layer sleep bad?

other issue is inner condensation wetting the bag. sales rep recommended opening the tent doors a bit at night. have to balance internal tent temp with keeping it dry.

what do you guys think?

Can you supply more detail?

What make and model bag, and what configuration and fill?
What conditions are you camping in, when are you warm and when do you get cold?
What shelter are you using?

I'd probably begin with a better pad--the Z-rest is a mild-weather pad and might be 90% of the cause for your cold nights. "Campcraft" might be part of it as well, as microclimates where you choose to set up your shelter can vary a lot from one spot to another. Condensation issues imply moist air and I agree with the sales person to try and ventilate the space overnight. Cool and dry usually beat warm and soggy.

Cheers,

Those pads have an r-value of 2.2, which puts them firmly in the warm season category. We just did 4 nights into the 20's with one 0 degree bag thrown over the 2 of us like a quilt. Both my wife and I have inflatable pads in the 3.5 range and we put a SOL emergency blanket foil side up on the floor of the tent. We were very warm. We also had gusty wind and 1 night spent inside the clouds. We had some condensation on our fly, but the bag stayed dry and lost no loft. Some dislike the tent we love because of condensation issues; we've learned to guy the sides out high when we suspect condensation issues will be present. We use forked sticks, piles of rocks, or whatever is handy to arch the side fly guy lines out to let the tent "breathe". The door always remains partially open, pointed away from the wind if we can. I suspect your bag is FAR off the zero rating. Compare it to the loft of some reputable bags that claim a zero rating. I have a bag with a 15 degree rating that I've taken below zero, so it also depends upon the sleeper. When the temps head for single digits and below, I use a bomber hat that is extremely warm, and sometimes even a balaclava under it. Beanies aren't enough sometimes and you want that warm, moist breath outside and not in your bag. That's also because we use our bags like a quilt so your bags hood may well suffice. We also upgrade our pads when ice, snow and low temps are on the menu. We use pads with r-values around 5 and sleep fine directly on snow and ice. As Rick D said, the pad may be your prime culprit if you are cold in the teens. I froze my butt off on a very unexpected cold, snowy Memorial Day in Vermont with a light pad. Bag was fine (and I was using it as a bag), but the cold just radiated into me from the cold ground. In the middle of the night I finally piled everything I had underneath me and caught some fitful sleep. The insulation in the bottom of a bag doesn't do much when it's compressed.

I'll +1 on the SOL emergency blanket on the floor of your tent. That will help keep you warmer. I use a piece of reflectix bubble foil insulation for a floor on my tent. I'll also lay one over my sleeping bag if I get cold and it helps. It will trap a little moisture, but it turns to frost on top of the bag at those temps.

My bag is rated down to 20º with a 32º "Comfort rating", and that's pretty accurate. I'm warm at 30º but slightly chilly at 20º so your's is probably similar when using the new ratings. I have a down jacket I use in cold weather and I'll lay that over my bag when I get cold too. It works great and keeps me warm when it's 15-20º

Cracking open the tent door will help with condensation. My tent will get a lot of that if I seal it up tight, but it stays a lot warmer too, so I usually try not to bump the walls.

Eating something before you go to bed will help keep you warmer too. That can make a big difference.

Now here's something completely different to keep you warm:

I made and use a "Super Shelter" style tent out of SOL blankets. It can be used with a campfire. Lot's of backpackers don't like campfires, and lot's of places don't allow them, but if you don't enjoy a campfire and can safely make one it's a pretty awesome alternative to being cold on long winter nights. You don't need a campfire going all night long. I make one to warm up the tent and my sleeping bag and crawl in while the fire is still going and let it burn down to coals. Depending on how cold it is I might stoke it up in the middle of the night, or I might wait until early morning. Either way it's really nice to be able to get truly warm. The tent only costs about $35 for everything needed, and it's pretty easy to make.

Here's a video that shows the tent while I ramble on about it a bit:



Here's a video of it with a campfire going and my grandson bouncing around inside: