Major Electrical Problems

Well I dont have an exact answer for you but you could always add up all the current draws to see if they'll exceed you 15A or 20A breaker whichever it is. Most things are labeled with a current draw but if they are only labeled with wattage then you can use the formula current=wattage/voltage (were voltage in the US I'd use the number 115). For example a 100W light bulb would be .87A but this only works accurately on resistive loads like incandescent lights, inductive and motor loads the actual current will be a bit higher. Computers might be a bit harder to tell their actual draw without measurement. I've got a 300W supply in my main system but its rated at 8A draw. Assuming I'm not using it near its maximum ratings I'd probably figure it for 4-5A but thats just a guess without measuring (and dont forget monitors and stuff are not included in that). To be honest thats a lot of working adding everything up.

I've been worried too since I'll be setting up a large tank in my family room, with a bigscreen and office in there two. And since the tank will probably be using 1200W worth of heaters and about 700W of lights I'll be pushing the limits of that 20A circuit and might even have to wire it differently. If the heaters and lights were on at the same time probably a vacuum or that electric space heater we use in the winter would probably put it over the top. I'm thinking the extra heat from the lights will be enough to keep the tank warm during the day so hopefully the heaters wouldnt come on during the day (or I could even program them to be set slightly cooler during the day). At least the utility room is on the other side of the room so if I have to wire it differently shouldnt be a big deal. Except that I dont have any spare slots on my breaker panel.

dont go screwing around inside an electrical panel unless you know what your doing.
one tiny slip, or a finger your not paying attention to touching some random thing is all it takes to get killed.

Now, depending on how everything was wired, it could be as simple as dropping in another breaker, and moving a few wires around. This way you would have the living room on one breaker, and the office on another.

dont add/"upgrade to" a 20A breaker unless you know the wiring in your house can handle it. the reason for having breakers is to cut off the power if a circuit becomes overloaded, AKA HOT, so if you have a 20A breaker in place of a 15, and the wiring cant handle it, then the wires could burn, or cause a fire long before the breaker ever trips.

fires inside the walls suck.

I dont know what 20L is, but add up the total amperage of all the devices you will have connected in each room, generally, a 15A breaker should be ok.

is the breaker that controls the living room/garage a doube pole breaker? or is it only a single?
(a double pole breaker has 2 "handles" that are both connected to each other, and they usually take up 2 panel slots.)

Again, I'm in the same boat lol... my setup keeps costing more and more and what I had originally though I'd have running early spring I know hope to have running end of summer. I'd definatly not try to DIY it unless your already familiar with electrical wiring. The code book is rather thick, and I dont know but I would suspect if one were to do wiring that didnt follow code, and the house burnt down, insurance may not even cover it? Not sure about that but think I read that somewhere. And let me tell you wall fishing in finished rooms and such can be a pain! I can do my own work for the most part but my problem is I dont have any breakers free - even though I have a small house yet a 200A service.

are you sure the entire garage and living room are on the same breaker? that seems kind of unlikely to me, and i actually think is against code to have more than one room on a single breaker (i could be wrong, if i am someone please step in and tell me)

it is possible that there are shared outlets, but having the entire thing all on one breaker seems odd.

old house or new?

LRC: Yes, if you do wiring in your house, and there is a fire, your insurance may be null and void if that electrical job hasnt been offically signed off by a licensed electrician.

im not exactly sure how it works though. It may not be a problem if its determined that it wasnt your wiring that caused the fire.... also depends on insurance companies etc.

Another thing to think about is if and when you planned to sell your house. My husband and I did a lot of wiring in our house before we sold it, when the inspector came through and noticed that there wasn't an inspection sticker it almost ended our sale (luckily there is an electrician in the family). In order for an electrical box to pass an inspection for sale it has to have a sticker on it from a licensed electrician (at least in DE and PA).