Interior walls are normally hollow.

I have a 1927 brick house with plaster and lathe walls and have run new wiring from the basement to the attic. Interior walls are hollow, but if you are going through two stories to get to the attic, these hollow walls are sitting on solid wood floors and normally have 2x4's on the top and bottom of the studs. So there is little chance of getting through them. What I did was pull the wire up along the vent pipe to the plumbing. In my house, the pipe went from the basement all the way up through the roof. I put a small weight on a string and dropped it down from the attic along the pipe. I then tied the wire on the string and pulled the wire up through both stories of the house.

If you have outlets in the attic, you could hardwire off of one of them. I put outlets in the outer plaster walls in the upstairs by using the same technique. I made a hole in the wall where the outlet was to go and then went into the attic and dropped the string and weight down and pulled the wire up through the hole to the attic. The lathe in my house is attached to 1x2's on the brick walls, so there is a small space between the plaster and brick. The floor boards run clear up to the brick though, so you usually can't feed any wire from the basement to the attic by going between the plaster and the brick.

Lath and plaster, ye' say (involuntary shudder). Fishing vertically, you also run into fireblocks (bad involuntary shudder).

If you run it up the outside of the house in the back, I don't think emt or sched 40 pvc conduit looks so bad. But that's just me. Personal preference.

Thanks Brickeye, Whitebrite and lonesparky95 for your helpful comments/suggestions. If we have a 240 v heater we would need to get the supply from the basement to the third floor as the existing circuit on that floor is of course 120v.

A couple of basic questions come to mind: is running wire outside allowed by code (in conduit I assume)and would a 120v heater be a possibility for the 150 sq ft space part of which is a shower room? Thanks again.

I'd do some more checking and exploring before you resort to running wire in conduit on the outside. First off, balloon framing was fequently used in the 20's and 30's, so you may not have fireblocks to deal with between the floors. But interior walls will still have the problem of the floor boards running under the walls. But, check the exterior walls some more - I've seen many cases where the floor boards do not go right up to the brick (depending on the direction they run). If that's the case here, and if your lathe is not attached directly to the bricks, then you might be able to drop a string with a weight or some fine sash chain (this works really well) into an exterior wall in the attic and have it fall righ out in the basement. You could try it and see what happens.

I usually find a first floor wall that is aligned with a second floor wall and then open up both.
Some runs of 1.5 or 2 inch EMT is then run basement to attic (non-metallic is also OK).
Repair the two stud bays and you should be good to go for a while.

Thanks again for all the information. Looking closer at the outside of the house we realize that what we thought was a tv cable wire is an electrical cable to the attic so we will follow this and add another for the electric heater. Given the height of this - sunken driveway beside the house to the third floor - we don't want to do it ourselves. So we just had an electrician around to give an estimate for a small (4') baseboard heater. We are waiting for the estimate but he said that installing a 240v heater would be twice the cost of a 120v one but would be a better heat. I can see that the unit itself would be more expensive and perhaps the labor a bit more but I can't understand double? Any comments welcome.

Just got the estimate. $700 for 4' 220v oil-filled baseboard and $550 for 110v. Taking into account that we are in the DC area and that there is a four storey height to run wire outside does this seem reasonable? Thanks

Not from the area, but it sounds reasonable. Concerning the path: there probably isn't any other way than to run it on the outside, unless, you want to make and patch holes inside.

I would suggest the 220v (which is actualy 240v). The amperage load on each wire is reduced in half. It will draw the same load as the 110v (which is actually 120v) but the 120v amperage is all on one wire and one phase of your electrical system. The 240v splits the load equally among the two phases you have in your home. 15 amps at 120v is the same as 7.5 amps 240v. The differences in the wiring is the change from a one pole circuit breaker to a two pole circuit breaker and the wiring will draw half the amperage so it can be smaller. If the difference in cost, $150, is for the change from 120v to 240v, I would ask for an explanation as to why. Granted, the 2 pole breakers costs 3 times as much as a one pole breaker. But that's it. Wiring should be a little less unless both required in the 15 amp wire range, then they would be the same. I would not pay that much for change in voltage without asking for an explantion. If the difference is somewhat due to the cost of the heater appliance itself, reduce the additional appliance cost from the $150 and see what the charge is for the 120V to 240V change.

Hopefully you have a good electrician and he made sure your electrical equipment can handle the increased load of the heater. Heating appliances draw more amperage than any other load in your home.

Thanks to all the help we got from this forum the attic heater is now installed with the cable going outside - in the end that was the easiest as the baseboard radiator was going to be installed on the same wall of the house as the electric supply box. What was unexpected was that the hydronic baseboard heater would have such a primitive thermostat (an extra). The baseboard heater unit is made by TPI and the thermostat,if you can really call it that, just has an Off mark on the control knob which you turn until you hear the click telling you it is Off. I was expecting it that at the minimum it would have some markings on the heater unit near the knob so you could remember where you set it. We had that on electric baseboard heaters we had 30 years ago. In the end we had a simple wall thermostat installed for an extra $120 but if the control unit on the unit had been less basic we could have done without this. I should have investigated the types of hydronic baseboards available and bought one myself to be installed but had read that there was little to choose between them which may be true.