Welding - it's not just for breakfast anymore

Whatcha gonna weld?

Steel. Mostly small parts and fixtures, with a few workbenches thrown in [;-)].
reader wrote:

Thermite doesn't use any gas.

Wirefeed - either fluxcore or MIG gas shielded. It's easy to learn, supplies and consumables are not inexpensive, gives good results.
If you are going to make those workbenches out of heavy gauge angle and tube, go for one of the smaller 220VAC input, 200A plus welding output units (Miller MillerMatic 210 or 251 or similar) and here's why...
It's better to get the biggest machine you can afford and envision using now, because as you learn and start doing bigger things, you quickly outgrow the 'baby' 120VAC input, 100A output class MIG welders - though they do have their places, like for tossing into the back of the truck to weld gate hardware and erect wrought iron fence panels.
And you get much nicer results with gas shielding, so get a welder already equipped for it. Straight CO2 is cheap for steel work, other argon or helium mixed shield gases are not - but you need the gas shielding for trickier materials like stainless and aluminum.
And watch the Duty Cycle ratings, the better welders have 50% to 100% duty cycle (depending on the output setting) meaning you can keep working till you're done. With a 10% duty cycle you do one or two welds and then have to stop and let the equipment cool.
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True, thermite uses no gas, but are you referring to using thermite to weld metal, like on railroads? Not the kind of chemical reaction I'd want in my building... My little Kidde fire extinguisher won't do too good with thermite...
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Wow. Lookit the prices... I feel like I want to rewire for 220v finally.
Bruce L. Bergman wrote:

That was tongue-in-cheek, Louis. A visit to a welding store or an hour with a welding text would quickly inform you about the various welding processes and equipment that suit his needs and wants, and what compromises are entailed by setting arbitrary constraints like "no gas". I wouldn't want thermite in my shop either, but it does meet the given constraints.
Fluxcore wire meets the constraint , but fluxcore wire isn't free either. While it might be OK for workbenches, it may not be suitable for small parts and fixtures. Gas can actually be quite inexpensive for small work because a little gas goes a long way when silverbrazing (or even welding) small parts and fixtures. CO2 for MIG (steel only) is quite inexpensive. Argon for TIG is considerably pricier than oxygen, acetylene or CO2.
Stick is inexpensive, no gas, great for workbenches but again not suitable for small work unless you're quite skilled. Few skilled welders would use stick as first choice for small jobs.

I was referring to flammable gases... One thing about the fluxcore is that some varieties should not be used in an enclosed space. Then again, CO2 can be bad as well, but it's non-combustible...
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If I could only have one type of welder it would be oxy-acetylene. For me it's the most versatile. I suppose acetylene gas indoors might be dangerous but probably not any more than natural gas appliances. And the acetylene bottle could always be kept outside except when in use. ERS

If your concern is not using flammable gases or shielding gases because you work inside, you can easily rig up a welding table with an exhaust fan to vent all the nastiness outside - the gases you start with are nothing compared to all the stuff outgassing from the fluxes and various metals while you weld. Like vaporized Zinc fumes from welding galvanized steel - suck that in and you'll have some problems.
If your main concern is about storing Oxygen and Acetylene cylinders inside, it can be done safely with reasonable care inside a properly built garage - one that has the US Uniform Building Code required cross ventilation grilles, and a turbine ventilator or two on the roof to ensure free ventilation and prevent extreme heat buildup.
Of course if you're in a condo or apartment with no garage, this can cause problems... This is when you start looking for cheap rental space in an industrial park for your workspace, or approach the Condo Board about renting that unused maintenance shop/storeroom out back.
I've saved a few small furnace blowers for making a fume exhauster - you can use a register boot adapter to change the square output port into a round duct, and then a simple length of flexible ducting to the nearest window or wall, and a 6" wall vent hood assembly.
The big trick is that you need a steady diffused draft over the welding work table, not a hurricane - much lower flow than if the exhausted work table was being used as a paint spray booth. If you can feel a breeze, you will have problems with the fluxcore or CO2 shielding gases staying over the weld long enough to be effective.
This is why furnace blowers are nice - they're multi-speed. Rig it with an Off-High-Med-Low switch, and the same booth can do double duty as a paint booth or a weld booth ** it's a belt-drive blower where the motor is out of the air stream. An air-over motor might be the ignition source if it's surrounded by high-test lacquer thinner fumes.
(And the other measures apply for a paint booth - line it with sheetmetal to contain a flash paint/solvent fire, seal the overhead fluorescent light behind a big sheet of Lexan plastic or tempered glass to keep the paint fumes away from the fixture, use disposable furnace filters to catch the paint overspray. And have two big [10 or 20-lb] professional class ABC fire extinguishers handy, though if you rig it for sprinklers you can make them medium size [2.5 or 5-lb]. Go look at how they build a professional booth, and scale it down.)
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All welding requires good ventilation. Stick welding and fluxcore welding, niether of which use gas, require considerably more ventilation than other processes. I won't use either process anywhere but outdoors, not to say that I never have. I used to stick weld in the garage during winter, had a 3600 CFM monster fan exhausting the fumes and forget about comfortable temps because no heater could keep up with the ventilation. Tawk about gas cost! I routinely do MIG, TIG and O/A in an enclosed space with modest but adequate ventilation even midwinter in Minnesota.

In my case, a Propane TurboTorch has pretty well replaced my O/A torch. The TurboTorch is not quite as hot as O/A but, hot enough for silver soldering. Also, propane is safer, not as expensive to operate as O/A, and available at odd hours at the corner gas station -- no more running out of gas on the weekend and waiting till Monday for a specialty gas supplier to open for business.
I have this one: 'm quite happy with it. Run it off a 20# propane tank.