Yes, yes, yes the dryer duct. Make it a regular chore.
How about a foam, or a powder based fire suppressant system? I’d have a slight bit more confidence in one of those two.
Very very expensive, and rarely if ever used in a residential situation…
I’m a fire protection engineer, I do sprinklers for a living.
There are three standards that are referred to when installing sprinkler systems: NFPA 13, 13R, and 13D. NFPA 13 systems are meant to protect the building and it’s contents, that’s the kind you see in commercial or large residential buildings. A 13R system is for residential buildings up to 4 stories tall, and isn’t quite as strong as a 13 system. The one for one and two family houses is NFPA 13D. The 13R and 13D systems are intended to protect life only - give enough time to escape prior to flashover.
A 13D system is intended to be cheap and easy to install. In most states, a plumber or even a homeowner can legally install one. In some states (Massachusetts, for example), only a licensed sprinkler fitter can install one - which drives the price up dramatically. These systems typically use CPVC pipe (faster and cheaper than steel to install), and are only designed to flow two sprinkler heads at around 14 gpm each.
Most domestic water systems fed by municipal water can’t supply 30 gallons per minute. There are also contamination concerns with sprinkler water, so municipal water departments require a backflow preventer between your sprinkler and their water system. That can be really pricey, and dissuades installation. Similarly, good luck finding a well that can do 30 gpm for 10 or 15 minutes.
Most 13D systems I see are supplied by a water tank in the basement and a 30 gpm irrigation pump. The pump doesn’t have to be a listed fire pump (which is silly expensive, and 13D is written around an inexpensive system). The tanks are usually 300 gallons, and filled via a manually operated valve to the domestic water system, almost always with an air gap to prevent a backflow issue. The pump is initiated by a pressure switch - when a sprinkler opens, pressure in the pipes drops and the pump kicks on. Theres also a switch that detects water flow that sounds a bell so you know if the pump is running (the bell can wake the dead). There are a few companies that sell pre built tank/pump units that will fit through a door so you can install one in an existing building.
The piping design is prescriptively spelled out in 13D. This length of pipe needs that diameter. Generally no real engineering is needed (but that can vary by jurisdiction), again to keep costs down.
Piping in the attic is always a little dicey. In the north, we try to avoid it if at all possible. NFPA 13D speaks to insulation thickness above the pipe to prevent freezing (dependent on where in the country you are). Even if you’re in the south, all it takes is one really cold night and your pipes freeze and burst. That’s bad.
My current house, built in 1952, does not have sprinklers. I have medium term plans to install them, but I really, really don’t want to hire someone to do it (I’m perfectly capable of doing the work myself, thank you). I am building a new home in northern New Hampshire that will absolutely have a sprinkler system.
You can read NFPA 13D for free (after a free registration) at www.nfpa.org/13D. The good stuff starts in Chapter 4.
You sound like a pro, but I’ll note that systems prone to freezing can be charged with air or glycol. Our previous system (vaulted roof at 10,000’ in CO) was charged with glycol…
Antifreeze systems are a pain, I avoid them if at all possible. You need a check valve between the regular system and the antifreeze side, and an expansion tank to account for the pressure fluctuating from the glycol changing temperature. Separate drains, a port to inject the glycol, additional control valves that can accidentally stay closed, etc. You’re supposed to have the antifreeze tested annually to verify it’s not breaking down in the pipe - no one does that. There was also an issue for years that the only antifreeze solutions that were available were flammable - whoops. That’s been solved in the past few years with listed fire protection antifreeze, but I still have some legacy head trash about it.
Sometimes there’s no way around it. A friend of mine has an antifreeze run for her attached garage (the rest of her house is plain water) as it isn’t heated. I’ve done some work on that system to relocate some heads, I didn’t want to touch the antifreeze side.
Dry systems are also possible (filled with compressed air), but they’re way more expensive and the piping needs to be run so it can be fully drained - no low spots, no pendent sprinklers (down pointing), and you need an air compressor to maintain the air pressure in the system. All added costs, and we’re trying to keep it cheap.
Well, that system is 23 years old (buy it a beer) and has never been subsequently tested. At least we don’t own the house anymore?
@KCB615, thank you! I was hoping there’d be a relevant professional among this group 
I did find a site describing the different standards, but it was in technical language referencing regs and guidelines that are beyond me. Your post is very helpful.
I live in rural South Carolina where there are very few requirements and codes for anything, which is great on one hand and not so great on the other. I’ve been trying to find a local company just to suss out my set-up and tell me if it’s even feasible or not, and maybe get a ballpark estimate to go on, but there ain’t much out there.
I have a mini farm here, and am very familiar with doing the pipes-in-winter waltz (since no one apparently believes it’s ever going to be below freezing for very long, and all the pipes are more or less at the surface 
) The difference, of course, is that I wouldn’t be able to let water trickle on the sprinkler side of things so I’d have to either insulate the attic or super-insulate the piping runs. Not impossible, but more $$.
Where would I go to find a local company (or person, really) that could install something like this, or even come look and tell me that I’m nuts to think of it? Would asking at the local fire station be of any use?
I love this board - you folks really are the best 
I did a few of these before. I was the eletronics guy that hooked a few of these retrofit sprinkler risers into alarm systems. If you live in a one story ranch with attic access its not the end of the world to put one in. Its basically orange CPVC 3/4’ pipes.
2 story and above houses are a little trickier, because you have to sometimes rip up the deck on the 2nd floor under the carpet to put them in.
It gets expensive if you don’t have enough water pressure to drive them. I had to help guys install a jockey pump with a big storage tank to drive sprinkler water flow on a 2 story house that got retrofitted to be a assisted living place in Texas. That was commercial grade though, but they used the CPVC type sprinkler pipes.
I have had to “pleasure” of cleaning up after the Ansul system discharged in my restaurant… I’d rather not have to do that at home…most commercial kitchens are designed to be more water resistant than home kitchens… you can use hoses, floor squeegees and deck brushes to slop the foam and powder residue out to back door or down floor drains etc.
I looked up how SC licenses sprinkler contractors, and if there are any exemptions. Turns out SC is pretty strict, only a licensed sprinkler contractor can install sprinkler systems, even in a single family home. There are a few exclusions but none of them apply.
I’d look to the Googles and search for sprinkler contractors near you. Most local fire departments might have an idea of nearby sprinkler companies, but honestly it’s more reliable to ask the interweb and see what kind of reviews are out there.
That’s fantastic info, thank you!