I have concocted an elaborate inground winter fig protection scheme. I've planted 10 in close proximity that I'm going to winterize by building a foam board house around all of them. Here's where the plan gets weird. Mydirect vent hot water heater and my direct vent boiler exhaust via PVC right near the plants. The plan would be to tap into this hot air source and pipe it into the enclosure. Of course this is flue gas so I don't think there will be much oxygen in it. Will it kill them or be fine?  The other option is just to pipe it through to the other side and let it radiate from the pipe. 

So, just to swag a few ideas, thoughts on this:

• First, all living and dormant plants need some oxygen level for the plants to stay alive; not sure what this level is at freezing temps, but I'm sure a lot less than during prime growing season.  I'd think there  would be enough mixing of fresh outside air with heated vent air, unless you go out of your way to make it air tight. ( Probably not good on either of your systems to have them venting into a closed space)

• Second, would your concoction maintain a nice even temperature? Or, would it fluctuate so much that you go way above prime dormancy temperatures, almost "waking" the plant up, then cold, then warm?  Wonder what the range of temps would be in your shelter?  seems like you want to create a just comfy zone, which might be hard to regulate given your system. 

You have to allow some fresh air to get to the plants. Otherwise they will sweat and rot. This has happened to my inground trees before during warm spells in the winter when I wrapped them air tight.
I cut them down to the ground and came right back up.

Rafed

Can you please elaborate on your Inground protection techniques?

Slingha

I wrapped them tight with burlap a few times around and then with a plastic tarp. Sealed the bottom with soil.
I think it was a combo of warm winter spells and the "Blue" color tarp I used that set their death sentence.

This Winter I will use a white color tarp but install a couple little vents made of 1/2 inch PVC pipes. One at the top and one at the bottom should be good enough.

I'm no expert but I think the combustion exhaust gases piped into a plant enclosure would be toxic to the plants. Plus, in a small space, I think the temperature could get very hot.
Most importantly, if you reconfigure your vent pipes, you might have issues of improper venting, resulting in carbon monoxide and other poison gases in the house. The plants might be the least of your worries. I vote no on the idea, but consult an expert. Good luck.

During my travels in and around Asia I saw Korean farmers wrapping fig trees in, what looked like, strips of burlap.  I looked to be 2-3" wide.  They did the same to Rose bushes in Seoul.  20-30f below is not uncommon.

Addendum - they also piled straw around the bases of the trunks

wasn't there a member who posted picture from korea here on the forum? using pipe insulation around the tree? that looked neat. i gotta start thinking about this since i'll be putting few trees inground coming spring.

Ive got a month to come up with something. 

my father did the pipe insulation and that alone did not work well. Now with other protection could work.. he is in zone 6 NJ by Ft Dix.

I agree, gas fumes can be very toxic to plants.
and you would probably get a wild swing in temperatures with that method.
from oven to deep freeze.

You'll probably only need the warmth of a single light bulb at about 30-50 watts turned on during the night, or very cold days to do the job.
Installing it in a large tin can, wrapped in fiber glass insulation with metal fly screen over the opening would keep it from catching your straw, leaves etc. on fire.  in a small, enclosed environment, a single light bulb could keep the insulated space at, or just above freezing.

Instead of mothballs, (which can also be toxic to some plants), i'd place an unopened box of Decon near the trunk, the mice will chew open the box when they get hungry. If no mice get in, the box is good to go for next year. 

Using plastic for insulation during the winter is never recommended, it traps too much moisture, which then freezes, and kills live plant tissues.
The idea is to keep out the cold, without holding in moisture that will freeze, and damage your plants.

I would not use or block any flow from heaters. If you build something around these it will make resistence and possibly cause back up of fumes inside of house and could cause death. Please avoid for your safety. DO NOT USE THIS IDEA. Sorry, but am concerned for you and others that might look into this method. My concern here is not plants, but human life and pets.


luke

I appreciate te responses. I guess I'm just going to build a foam board house and build a "window on the top to let light in. Then pray.

I would just cover them with leaves, straw, or hay and some protection to keep them dry like a tarp. If you make it too nice and cozy you'll be inviting mice and voles to a luxury hotel to stay and dine on your trees. I agree with the others on not doing the furnace exhaust setup, it will only spell disaster. Necessity is the mother of invention and I'm sure you'll come up with a better way. Good Luck!