A device in the form of an insulated cabinet is mounted on the wall beside (and inside) the entrance door to your residence. At the bottom is a small hatch; as visitors enter they open the hatch and take out a hot hot water bottle. When they leave at the end of their visit, they pop their now cooled bottle into the top of the cabinet.

Of course, if your bottle goes cold you can always go to the cabinet, pull a new one out the bottom and put the cold one in the top.

Inside, is a stack of bottles. Each one has electrical contacts which engage with contacts in the cabinet. So when a cold bottle is put in the top, it starts heating up. An internal thermostat cuts off the power when the bottle is up to temperature.

The cabinet of course is well-insulated so that the bottles can be kept warm ready for use, without wasting too much heat.
-- pocmloc, Jan 20 2014

or you could "nuke" them; probably easier than having each water bottle carry its own element.

In a recent power outage of a few days, I employed "manual hydronic heating" to keep the place up around 15C/60F : just kept filling up pots and pans from the water heater (gas with electronic gizzardry on a rechargeable battery, situated close enough to the chimney that it didn't require a mains-powered exhaust fan) and distributing them around the domicile.
-- FlyingToaster, Jan 20 2014


How long does "nuking" take? I am looking for sub-2-second retrieval at the front door.
-- pocmloc, Jan 20 2014


<wistful>

You know, I don't think it's ever, in the history of civilisation, gotten down as far as 15C here where I live. Our problems trend more towards wanting to remove our skin, or how to implement personal blast chiller suits - especially lately.

Maybe we could open a portal between your place and mine, share some entropy?

/<wistful>
-- Custardguts, Jan 20 2014


Custardguts, how about a really long heat pipe, from your place to mine?
-- goldbb, Jan 22 2014


In a recent power outage of a few months* I employed "Muhammad-to-the-mountain hydronic cooling", and sat in a bath filled with cool water.

* I'm exceptionally stubborn when it comes to dealing with bastard utility retailers.
-- spidermother, Jan 23 2014



random, halfbakery