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Discussion Starter · #1 ·
...except when they're not!


I installed a new tankless natural-gas waterheater on a time-crunch, which means I didn't get to do it "right." It works, but I need to take care of a couple of important things, and I could use some advice.


First, the vital statistics. The new water heater is an Eccotemp FVi12, which is a small 74,500 BTU unit, just the right size for us. We don't use a ton of water, and the old house only has one full bathroom, so it's not like we need a high-demand unit. Trouble is, all this thing's connectors are smaller-than-usual sizes.


Here's what I *didn't* do yet: I need to install the isolation valves, which I can't find, because the thing runs off a half-inch line instead of 3/4. Question one is, does anybody know where I can even FIND a 1/2" valve kit? If not, what happens if I install a reducer and use 3/4-inch valves? Is that gonna mess with my flow/pressure/etc.? And if I hook up a descaler--which comes with a 3/4-inch hose--and use an adaptor to hook it up to a 1/2-inch valve, is that gonna mess up my water heater? I plumbed in pex, and I planned ahead for cutting out some line for the valves, I just don't *have* them. If I can't attach the isolation kit, how should I do the T&P valve, and is there an easy way to do some kind of diverter so I can still use a descaler?


Second question, with preface: I'm not afraid of plumbing, but I don't know everything, and I have a healthy respect for gas lines. I plumbed gas to the unit, and did my leak-checks. Found one at the flare coupling at the end of the flex line, and fixed that. I don't see any more bubbles, and I don't *think* I smell gas, but paranoia rears its head. I don't have the money to hire a plumber, and I needed the unit installed, so I just did it, and I've done all the due diligence that I can... but I was wondering what else I can or should do to double-check that there aren't any leaks. What's the gold standard for ensuring leak-free gas plumbing?


And the third question, which is one I actually didn't quite think through before jumping in. The unit is installed in the basement, and per the manufacturer's specs, there's plenty of air available for combustion. However... we also have a wood-stove down there, which is the heat-source for the house. How do you do the calculations to figure out whether or not you need a dedicated air source for combustion appliances?


Finally, one last thing about gas. The old gas piping is kind of... old and weird, and now that the water heater has moved, I'm going to clean it up some. The three appliances that use gas are the range, the water heater, and the dryer. The gas line comes in, turns parallel to the wall, and runs past a tee to the range, past the water heater, to the dryer, so there aren't really many turns and complicated runs. Right now, it drops to 3/4" from 1" at that tee, then steps down again from 3/4 to 1/2 after the water heater. Does that seem pretty reasonable, or should I do some reading and calculations?


Thanks so much for any advice!
El Barbón, refreshed after the first hot shower of the new water heater



The old water heater is a martyr to the cause; I retired it because it was leaking a disturbing amount of water and I don't want a swimming pool for a basement.
 

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Oh, one more thing. There is a fair-sized (~ a fat eighth) gap at the wall thimble around the vent pipe (2", because again, why make anything an easy-to-find size). The whole thing is stainless, so I don't want to just stuff the gap with tinfoil. :p What's the best way to close that up?
 

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Oh, one more thing. There is a fair-sized (~ a fat eighth) gap at the wall thimble around the vent pipe (2", because again, why make anything an easy-to-find size). The whole thing is stainless, so I don't want to just stuff the gap with tinfoil. What's the best way to close that up?
Metal Fire stop. Basically a square piece of sheet metal, at least 24 gauge, with a hole in the middle to fit.

Cheers!
 

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They make 1/2 valves. Shouldn't be hard to find, but 3/4 won't hurt either.

The gas line sizing sounds OK, but I'd need distances and btu consumption for each appliance. (not just the water heater.)

To check for gas leaks, soap and bubble is a valid test. If you don't have leak soap, I suggest undiluted liquid dish soap. Another test is to read the meter. Turn off all gas appliances. Take a note on the meter reading, paying attention to the lowest volume indicator. (whether that's a dial or digit.) check back in 30 min and see if it's changed. No change, means no leak. The longer you wait, the smaller the leak you'll be able to spot. An hour or 2 is way more then enough on a system that small.

For fresh air, there's calculations for wood stoves and other calculations for gas appliances. You simply add it all together and see if you have enough. (4 square inches is the smallest we can go here. You'll need roughly 1 square inch per 1000 btu of gas appliance, assuming no natural draft units.) What size of venting do you already have?

Cheers!
 

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Discussion Starter · #5 ·
They make 1/2 valves. Shouldn't be hard to find, but 3/4 won't hurt either.

The gas line sizing sounds OK, but I'd need distances and btu consumption for each appliance. (not just the water heater.)

...

For fresh air, there's calculations for wood stoves and other calculations for gas appliances. You simply add it all together and see if you have enough. (4 square inches is the smallest we can go here. You'll need roughly 1 square inch per 1000 btu of gas appliance, assuming no natural draft units.) What size of venting do you already have?

Cheers!
They make 1/2 valves. Shouldn't be hard to find, but 3/4 won't hurt either.

The gas line sizing sounds OK, but I'd need distances and btu consumption for each appliance. (not just the water heater.)

...

For fresh air, there's calculations for wood stoves and other calculations for gas appliances. You simply add it all together and see if you have enough. (4 square inches is the smallest we can go here. You'll need roughly 1 square inch per 1000 btu of gas appliance, assuming no natural draft units.) What size of venting do you already have?

Cheers!
Thanks! First off, I *did* manage to find the half-inch valve kit, and the supply store has ordered it. Silly me, I never got around to checking RV supply places.

As for venting... When we moved in, there was a smallish tanked heater rated at 34,000 BTUH venting into the same chimney as a 100k gas furnace and a wood stove. I *believe* it's a six-inch opening, but don't quote me. At any rate, the wood stove (an old Fisher baby bear) is the only thing using that now. The new water heater has its own two-inch vent through the wall. The basement is roughly 5040 cubic feet, and according to the manual, the water heater needs about 3725 cu.ft. to be considered installed in an unconfined space (they say 50 cu.ft. per 1000 BTUH). That's actually... kind of pushing it, isn't it? I mean, the old basement is plenty drafty -- when you sit in line with the door going up to the woodshed, you can feel the draft when the stove is going -- but I'm wondering how borderline it is when the stove is fired up and the water heater is going.

As for demand, the range could theoretically pull up to 67,000, the water heater is 74,500, and the dryer is 22,000. From meter to dryer is under 30 feet, from 1" tee into 1/2" pipe into range is roughly 30' as well, although that pipe has a ridiculous number of elbows (eleven!) to route it under and over ducts and joists and girder.

Also, I did find the suspected leak, after I went and got a sniffer. It didn't bubble that I could see, but that at least explains the faint whiffs of gas I'd been getting. Yeesh.
 
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