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Help with install of tankless water heater
Old 01-21-2011, 10:42 PM   #1
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Help with install of tankless water heater

Hi all, I'm in the process of replacing my traditional water heater with an exterior tankless model. The general process seems pretty clear enough, but some of the details are a little lost on me, so I figured I'd hit up the best (only?) forum I visit to see if anyone has any experience with this...

Some background first: My current water heater is a 50-gal, 20 year old, natural gas model in the garage. My plan is to extend my water and natural gas lines to the exterior wall of the garage, where the tankless heater will be mounted. Power is via standard 120v, 3-prong plug.

1) My water pipes are copper, so I expect to run additional copper pipe to the wall, but is it safe to have exposed copper piping outside? Or do I need to go with the old school iron pipes on the exterior connected via brass fittings to the copper on the interior?

2) I'm concerned that the part of my wall where I drill through to push the pipes out will not be all that well supported (just drywall on the inside and stucco on the outside) - what can I do make sure the pipes are not going to jostle around? I can always caulk up the gap to ensure it's protected from the elements, but I'm worried about my kid bumping into the pipes from time to time when playing outside.

3) I'm assuming I should ground the exterior pipes - but there seems to be conflicting info on the web about whether I can just sink a grounding pole near the exterior pipes and connect them up, or if I need to connect the ground to another ground in/near the house - anyone know anything about this?

4) The installation of my new heater requires a 3/4" gas pipe - but my current gas pipe to the water heater is only 1/2". The new heater has a BTU rating of 150,000, so at first I thought I was going to have to have a new gas line put in for the water heater, BUT: the current gas pipe is only about 10' from the gas main into the house, so I'm thinking that the heater should get adequate gas. Based on some research, it looks like 1/2" at a 10' length supplies the same gas volume as 3/4" at 40'. Is this wishful thinking or reasonable?

Thanks to all you DIYers for any feedback on the above.
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Old 01-22-2011, 02:48 AM   #2
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Caulking should be adequate for the stucco penetrations, assuming you are in a mild climate (no freezing temps) . On the gas line, go with 3/4, and make that a direct line to the meter. 150k btu is one of the smaller tankless units, many are well over 200k btu, however , the original 1/2 line is prob. tee'd off of a line feeding the rest of the house. Undersizing at this point of connection , the waterheater will prob. still work, however , other gas appliances downstream may exhibit problems when everything is running ( furnace, range, clothes dryer and waterheater all at once).

Another thing is the capacity of the gas meter. Residential meters and the associated pressure reg. usually can handle 250k btu or 400k btu. Look at the size of the "Spud" connections to the meter (half unions on the meter) they are usually 1/2" or 1". The riser line from the street can supply a higher capacity meter just fine.

Add up the total of all your appliances. clothes dryers are usually 15-20k btu, kitchen stove with 4 burners, about 65k, and furnaces, anywhere from 45-140k btu. pool or spa heaters 60-400k btu. If the total is much over 200k btu, consult with the gas company.

Gas suppliers are usually quite happy to changeout your meter to a higher capacity at no charge , as they see additionl ga$ revenue $$$$.
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Old 01-22-2011, 05:10 AM   #3
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We sometimes have issues with our 2nd tankless (which is about 40 feet away from 1st tankless - gas supply is on the far side of 1st tankless) if too many other gas appliances are going at the same time. I've noticed that it is better to turn the furnace on for 10-15 minutes to take the chill off in the morning, the turn it off before taking a shower from 2nd tankless. Otherwise "sometimes" the 2nd tankless will not fire for 3 cycles of trying to light, then will go into error mode. That means I have to shift all the junk stuff in DD's closet, go in the attic, and reset it. Not a huge problem, just a PITA, but probably could have been avoided with a larger supply line, or can be avoided by turning off one or two other gas appliances first.

YMMV

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Old 01-22-2011, 07:55 AM   #4
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Quote:
Originally Posted by skyline View Post
1) My water pipes are copper, so I expect to run additional copper pipe to the wall, but is it safe to have exposed copper piping outside? Or do I need to go with the old school iron pipes on the exterior connected via brass fittings to the copper on the interior?
I'd use copper. It is more corrosion resistant than galvanized steel pipe

Quote:
2) I'm concerned that the part of my wall where I drill through to push the pipes out will not be all that well supported (just drywall on the inside and stucco on the outside) - what can I do make sure the pipes are not going to jostle around? I can always caulk up the gap to ensure it's protected from the elements, but I'm worried about my kid bumping into the pipes from time to time when playing outside.
I don't think that support of the pipes is a big deal, but if you want, glue /screw a 1x4 to the outside wall, then drill through it. If your walls have fiberglass insulation, don't try to drill thorough it. The fiberglass will wind around the drill bit and make a hellava mess. Instead, drill through with a coat hanger as a bit and drill the walls from each side. Part the fiberglass for the pipe.

Quote:
3) I'm assuming I should ground the exterior pipes - but there seems to be conflicting info on the web about whether I can just sink a grounding pole near the exterior pipes and connect them up, or if I need to connect the ground to another ground in/near the house - anyone know anything about this?
Won't it be grounded by the three prong plug and the extended water pipe? Heater instructions should be specific about this - can you find a PDF installation manual on the web?

Quote:
4) The installation of my new heater requires a 3/4" gas pipe - but my current gas pipe to the water heater is only 1/2". The new heater has a BTU rating of 150,000, so at first I thought I was going to have to have a new gas line put in for the water heater, BUT: the current gas pipe is only about 10' from the gas main into the house, so I'm thinking that the heater should get adequate gas. Based on some research, it looks like 1/2" at a 10' length supplies the same gas volume as 3/4" at 40'. Is this wishful thinking or reasonable?
If it is easy, I'd upgrade the pipe diameter.
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Old 01-22-2011, 11:03 AM   #5
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I'm glad Travelover brought up the grounding issue. The appliance using it's 3 prong plug is indded the correct method.

All metalic pipe in the structure needs to be bonded to the grounding system on any dwelling. The best way is to buy 3 or 4 ground clamps and some #6 copper wire. Attach to the hot ,cold , and gas line and connect together.

The reason for not using a seperate ground rod, is, if a large groung fault ocoured in your house , or even anywhere between this rod and the transformer on the power pole, and this ground rod has the least resistance to ground (earth) that fault current will chose that point and send the entire current available from the power pole transformer (up to 20,000 amps) through your house wiring for a split second ! It's not pretty.

Exceptions, If the electric service is not bonded to the cold water service, or if any of the water supply system is plastic, you also should run this to the ground rod (or ground loop ) at the electric service, and while you are there , check to make sure the elec service has a good connection to the ground rod . (things get loose over time)

Another exception, if you live a house with corrigated stainless gas line , aka C.S.S.T ,( looks like orange or yellow vinyl covered flex tubing),grounding this type of gas line has been found to sometimes cause pinholes in this tubing in the event of a lightning strike nearby

Hope this is confusing informative.
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Old 01-22-2011, 12:26 PM   #6
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You could also post your question at terrylove.com. It is a plumbing site with an active discussion board. Terry Love's Plumbing & Remodel DIY forum

Good luck!
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Old 01-23-2011, 02:31 AM   #7
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Thanks everyone for your responses - I think I'm all sorted out on everything except the gas line:

I actually ended up ordering a Rinnai R75LSe, which maxes out at 180K BTU. Unfortunately, my meter maxes out at 200K BTU, so I'm going to have to work with the gas company to see about getting a higher capacity meter. Between my BBQ, the central heater, stove, dryer, and this new water heater, I think I'll be pushing 350-400K BTU peak.

Thanks again to everyone...
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Old 02-11-2011, 02:18 AM   #8
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So, finally managed to get everything done, water heater's working great. I figured I'd post a follow-up in the event anyone finds this thread while searching on tankless water heaters:

Gas: I ended up calling the gas company as Lakewood suggested, and sure enough, they came out and replaced by 200K BTU meter with a 250K BTU meter (they measure max capacity by adding up the BTU of all gas appliances, divide the total by 2, then add 10% of the highest BTU usage appliance). They were nice enough to put in a new Tee that I could use to supply my new water heater, so I ended up putting in 3/4" black pipe after all.

Water: I had to drill 7/8" holes into my stucco to run the water pipes. For whatever reason, my local Home Depot didn't have anything that could do this, so I ended up drilling a bunch of 1/4" holes using masonry bits, then chiseled out the first 7/8" hole, which took forever. For the second hole, I still drilled out the 1/4" holes, but then used a Dremel to grind out the 7/8" hole. The Dremel cut through Stucco like butter, but created a LOT of dust. Still, it was a lot faster, and I would probably go the Dremel route if I didn't something like this again. Once the holes were in, it was simply a matter of cutting and sweating the copper pieces to reroute my water pipes from where the old tank water heater was to the exterior tankless model.

After that, it's just plug in the power and take a shower...
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