My wife and I are thinking about buying a funky old house where we live, in southern Ontario, and trying to prioritize upgrades. There's a lot of knob and tube to replace — top priority — and some old iron plumbing stacks that will probably be second tier.
Third tier gives us lots of options, but nothing mission critical like the wiring or the plumbing. One strong contender is replacing the hot water rads, which are all those old baseboard "public school" style — large metal boxes with dials on the front — and seem to be several decades old, at least. The boiler system seems to date from 2002 and has been inspected annually and seems to be, on cursory inspection, in good shape.
The question is obviously if there's a huge efficiency gain in upgrading them. The utility bills (for the gas-heated boiler, plus electricity) from the previous tenants seem high, but they're also fairly wealthy and quite elderly, so they may have just kept the place jacked to 80 degrees all year round without much thought to consequences. Windows are about 80% upgraded, so there's work to be done there as well, but I'm mainly wondering if replacing baseboard hot water rads with new models is a "pays for itself" upgrade or mainly an aesthetic choice.
EDIT: Here's a not dissimilar picture to what we're looking at: this style, but twice as deep (it extends twice as far from the wall), and with a knob in the middle of the vents. I've assumed the knob opens/closes some sort of valve, or controls something with the vents, but I cheerfully acknowledge that I really don't know exactly what's up with these.
Best Answer
Why is knob and tube top priority to replace? It's quite safe if left alone. You only need to replace it in visible areas: the stuff behind the wall doesn't need replacing.
You might want to add some circuits in certain rooms, but you don't have to remove the old ones.
No upgrading the radiators (from your description they don't sound like baseboard heaters) will not increase efficiency. Forget about "huge efficiency gain" - it's doubtful you will have a gain at all.
What might increase efficiency (somewhat) is balancing them. An old house like that probably has only one zone, so you need to adjust the settings on each radiator so that the house is balanced - that some rooms do not end up hotter than others.
This can take a long time to do. To start with, do nothing - someone might have already done it for you. Then see if the rooms without the thermostat are hotter or colder than the one with. If all the rooms are hotter/colder, then adjust the radiator near the thermostat the opposite way.
Now that you have it mostly set, start adjusting each room based on the temperature. Wait like a day between each change and be aware the correct setting may vary based on the outside temperature, which is annoying, so you'll just have to find some reasonable midpoint.
If you want to upgrade anything it should be the insulation on the house.