Gas Tankless Water Heater

3,119 Views | 20 Replies | Last: 6 yr ago by Naveronski
Naveronski
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AG
We're buying a house, and looking to replace the existing water heater with a tankless one.

1) House was built in 1955. Very tiny water heater/washer/HVAC closet.
2) Existing 40 gal waterheater is still working, but dated.
3) Because closet is so small, we're looking to replace WH with tankless gas model, allowing a normal sized washer/dryer.
4) Relocating washer/dryer to another part of the house is possible, but would be expensive, and a pain in the ass, given locations of power/water/drainage.
5) 2 bathrooms + washing machine + dish washer.

How big of a unit do we need? What brands does TA suggest? What should we avoid?

Thank you.
213 Grove
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AG
Rinnai, Navien, and Rheem.

What size gas line do you have to your heater?

Naviens can run on a 1/2" line while most others require a 3/4"...also Naviens can be vented with PVC pipe while most others cannot which helps reduce costs
toolshed
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AG
I was going to suggest Navian as well, for the reasons above. They also have a integral circulation pump, if you have access to one of the farthest hot water lines, either in the attic or a crawl space, or can get it to a hot supply easily. You can then have a hot water loop and instant hot water.

The PVC exhaust vent alone is worth it!
The Fife
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I'd add Tagaki to the list. A lot depends on your gas line size, what kind of draw you're expecting and how long the gas line run is from the meter.
LostInLA07
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AG
Curious how much is costs to run the internal pump to have instant hot water? Ours has one of those but I'm worried about my gas bill if I run it too much. Doesn't that basically cause the heat exchanger to run continuously?
strohag
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AG
Rheem condensing units also vent with PVC
Naveronski
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AG
I don't know what size the existing gas line is. I think it was 3/4", but I'm not positive.

Is there any reason I can't tie into an existing vent? I'm looking to put the tankless heater in roughly the same location as the current water heater.

Thanks for the information so far!
Rexter
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I replaced a tank with a tankless in the same spot. You will need to change the vent pipe. The only modification I had to do was enlarge the hole in the ceiling in the garage. The new vent was the same size as the old one. Gas line was already 3/4".
The Fife
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Naveronski said:

I don't know what size the existing gas line is. I think it was 3/4", but I'm not positive.

Is there any reason I can't tie into an existing vent? I'm looking to put the tankless heater in roughly the same location as the current water heater.

Thanks for the information so far!
None that I can think of unless it's not large enough - I've seen models that are ok with PVC pipe as a vent.

The size of the gas line is important, but also how long the run is and how many bends there are. It all adds up to how much power you'll get out of the burner.
Rexter
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The vent pipe on an indoor unit serves as intake and exhaust, so you have to replace the old exhaust pipe.
Naveronski
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AG
Well, apparently the gas line is only 1/2". Hopefully that doesn't disqualify my plans.
213 Grove
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AG
Naviens run 1/2" no problem
chap
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AG
Not to hijack, but any recommendations for Navien sellers/installers in Houston/Woodlands area? I'd like to look into this.
62strat
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AG
LostInLA07 said:

Curious how much is costs to run the internal pump to have instant hot water? Ours has one of those but I'm worried about my gas bill if I run it too much. Doesn't that basically cause the heat exchanger to run continuously?
This;
A circulation pump on a tank makes sense.. there is 40-50 gallons of hot water there at all times, why not circulate it?

But for a tankless, you are now basically running it all the time, just to have hot water to circulate.
strohag
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AG
It's because people are stupid and think that they need instantaneous hot water. Waiting a few seconds for hot water in this day and age would be a travesty.
toolshed
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AG
I'd do some research before claiming people to be stupid.

I've had customers that we're tired of waiting 3-5 minutes for hot water in their bathroom in the far end of the house from the water heater location. One had to get up, turn on the shower, brush his teeth and use the restroom before the water was hot enough to take a shower. It's a convenient comfort for sure, but some people choose to spend their money on comfort, and I'm happy to do the work for them to earn a living!!

Navian heaters have a small storage tank that holds hot water and circulates from that. How does it work? I'm not a plumber, nor do I claim to know the ins and outs of heaters, that's what I rely on my plumber for. But here's a link, read up, and if you're interested, contact a qualified plumber to get more info and weigh the pros and cons. In the circumstances of the op, gas line, etc. Navian is an option they could consider.

http://us.navien.com/TechInformation/Details/3
strohag
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AG
3 to 5 minutes sounds like a plumber did a crappy job of piping a house. No way a line should take that long to clear out cold water from a line. Tankless is the way to go and Navien is a good product. I'd tank Navien and Rheem 1a and 1b.
toolshed
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AG
I couldn't tell you what a plumber did 20-30 years ago. I can however suggest solutions to a problem.

I didn't believe it until I saw it. Overcoming the cold mass around a pipe on cold mornings can take some time if the water in the pipe, the pipe, and surrounding soils are cold.
Naveronski
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AG
We won't be adding a circulation loop at this point.

That said, Navien looks like a good option.
62strat
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AG
Can someone explain a circulation pump on a tankless? Does it just run all day creating hot water just to circulate it?
tmollre
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AG
Moore Supply in Conroe did a counter day with Navien this week. Give em a call. 936-756-6663
Naveronski
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AG
I'm trying to figure out the BTU's of my house.

From the gas main, I see:
R-275
275 CFH
14-W
250 CL
5 PSI

From searching, I think that means we'll have 275,000 BTU available; more than enough for a Navien unit.

Yes?
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