I browsed a few more stores including one of the many nursery stores that carries flower tie wire and another store that carries this green painted wire. Mine runs 0.19 ohms of resistance per foot and close enough of a number to go by because by the looks of my wire thickness it's about the same as advertised here as 26 guage;

• Floral Wire

The problem now is trying to get a few volts throttled down from a 12 volt battery to make something energy efficient enough to enact the 270 feet of green insulated iron alloy now. So if an electronic sensor type device that belongs to a heat mat that won't be part of this is still an option then of affordability then there's still this 2-3 volt power supply needed here to finish the circuitry portion of this possible project that I'm geared up for myself at least.

By the way, the help desk at Portland nursery sees eye to eye on all of this that apples and plums can be reliably air layered with heat this month. It's necessary to beat dormancy of the wood in this point of the year so in PNW conditions there are several weeks yet.

Redbud said
Can anyone offer advice on how late in the Fall apple trees can be airlayered for replanting?

This Spring I grafted onto watersprouts of G.16 rootstock from a tree that was cut down. I cannot dig the waterspouts due to them being too close together and connected with large roots of the old tree.

  

Following this discussion I'm inclined to think that your intention is to invoke roots on your grafted rootstock. I'm not so technically inclined and I don't know your location but I think what I'd try (I'm a small scale hobbyist, yard not acreage in the Portland area).    If you've grafted high enough, mound dirt or other growing medium, amended soil, volume and height, enough to not be weathered away through the winter and to modulate temps. High enough to not cover the graft, but a fair way up the stems of the rootstock suckers. I'm thinking 6-8" or so, more if you've got it. Maybe a knick here or there in the covered area to see if it makes a difference in encouraging dormant buds to form roots during the remaining fall and in thru winter. Mulch it if you have materials to extend warm time. Come late spring uncover a bit to see what progressed. If you think it looks good, take your transplanting spade, slam it down between the old trunk and your now more rooted, grafted stock to sever it/them from the major root mass. Maybe take some extras for the next grafting session if it worked well and if you're liking the rootstock. Pretty sure this approach would work around here, and based on that your rootstock is suckering I'm thinking they should want to make roots if given the opportunity.

Jafar: I think over the period of the last few days that Redbud has started to realize that all posts that have come in are way too far from Chicago zone 5a, so the hunt here for answers might be over.

Larry said: Rooney, what is your target current or wattage for the 270 feet of wire?

All of that about wire guage vs. wire length estimates needed were as a possibility so that I could heat about 6 hardwoods at 2/3rds watt each. I used a long section of the green paddle wire which is iron based and over 150 feet of it trickled my amperage down to .31 amps when hooked to my battery at 12.5v. The green insulation all balled into a big mass didn't heat much or do any damage to the green insulation. So I could have gone with the green paddle wire by separating the big mass into the 6 individual air layer subjects if I'm patient enough but I'm not. 

So instead I picked up a used ConAir dryer and removed the bi chrome elements. Unlike toasters they are coiled up inside and to further save space they run them in 6 rows that measure 6.5 ohms each. One set stretches to 2 feet so I can easily twist around my targets. Up to this point enough values are given to I think answer your load balancing question (or curiosity). ..and as well no voltage reducing devices are going to be needed either. 🙂

What I'm getting at, and kind of achieving in engineering so far, is a constant .3 amps from a whole series circuit to a car battery, and no voltage reducers. ..battery juices up 6 elements at 2/3 watts in each.

The next hurdle that I faced with now is insulating the elements from corrosion or touching each other and as I wind them around the respective targets. Duct seal (clay vaseline mix) should work to build up around the target points of the tree and work as an element/conductor insulator (to prevent touching) and well enough at cool enough temps (~65F) to not melt away. 

The final touches required are feedback mechanism to up or down regulate the temperature set point so the best way I found to do that is a 55 dollar Wilco heat controller that has a remote sensor the size of a section of cutting. The product powers with household voltage and has the 120 volt plug that is meant in this case to cycle a 12 volt DC transformer and not any battery for this at all. The product will take one spot of my 6, so I'm getting 5 maximum possibilities at this point. The product does display live temperatures. This feature would allow how much laying around of extra blanket strips necessary to build the correct rate of heat.