We'll be running an portable, oil heater in the kid's room, and probably will look at getting a second for ourselves.

Rev. Cyc. AC is super expensive to keep running, so we use it to take the edge off and then maintain the temp with the oil heater.

Layered Clothing also is a big help. (Think bushwalking or trekking)

Whatever makes you warm, that's what I say. I have my little heater I carry around the house with me. It's not gonna heat the house, but with tiles, no carpet, and so many high ceilings, heating the rooms is pretty much impossible anyway.

A tip if you are gonna get a heater at all... get one now. Last year when the cold weather really set in they all sold out really fast, and the only ones left were marked up by about 500%.

I've also refrained from using my reverse cycle air conditioning because of the cost. I have portable heaters that I bought in HK (very convenient for the bathroom-it gets really chilly fast as soon as you get out of the shower or bath). I've also started wearing socks and long johns inside the house.

I guess I have more of an aside question to this...how much colder does it really get? I haven't really felt that cold this year, at least nothing that wearing socks and a sweatshirt around the house hasn't fixed, and am not sure if it's really worth investing in a heater, especially as I will be leaving for HCMC in about 3 weeks and will not be returning to Hanoi until late-February. What do all you experienced-Hanoians think???

It's not cold in Hanoi just yet. The few cold days we had last week was just a small taste of what Hanoi will do. Last year was the coldest in 20 years (so I've been told). It didn't really start getting cold until around this time. I suspect it will be much colder in January and February than it is now.
It is also going to get a much wetter, not in the form of rain, but in the form of humidity. The walls will start to cry with moisture and your clothes, bags, and book shelves will start to mold (for real).
What to do? Wear layers, find a warm and wind proof jacket. Make sure you do your laundry long before you need it. It will take days to dry. I have found my clothes dry much faster inside than outside this time of year.
Also, I go the space heater way. I bring it from room to room and make sure I turn it off when I go. I also never use a power strip for my heaters; I fried about 3 last year before I got the idea.
I also bought a few electric water bottles. These things are great. All you need to do is plug them in for 5 - 10 min and they stay warm for hours. They are wonderful!
Bundle up, it's going to be a long few months.

The cool thing about running the aircon on heat cycle is that it dries out the air in the room. Without this the cold really bites into the bones.
And I think running air con may be more economical than running a 3 or 4kw portable electric heater. I did that in the exceptionally cold weather last winter and my electricity bill shot up by 4x normal.

One thing I do know - if you run your wall heater make sure you clean it out to make it more efficient and not waste elec.
Maybe you dont know, or might expect your cleaner to do it - but it is often forgotten. Open up the front hatch and take out the dust panels, there are usually 2. Hoover them if you can, or wipe them - they are usually covered thick with dust.
I did this with my current heater (which looks like it hasnt been cleaned in years) and it has made such a difference. I can now heat my bedroom in minutes as opposed to an hour!

Can anyone please let me know where I could purchase an oil or gas heater?

My cell phone number is 0938384064.

Thanks.