Tankless water heater install?

[nola mike]

I'm thinking about replacing my 25+ yo 40 gallon heater with a tankless model. Been looking at this one. I currently have 3/4" gas to the old heater (my whole house is I think under-supplied with 3/4" main, but the city keeps on insisting that it isn't...), and 1/2" water. It's vented through a chimney currently, but the location is right next to an inoperable window, which would be a good place for horizontal venting. I have no problems with hot water supply currently. Questions:

1. All the tankless heaters that I've seen specify 3/4" water. I have 1/2" main supply to the house, which is 100 years old and isn't getting changed. Currently no real issues with water pressure. I'm unsure how this will impact the amount of hot water through the heater. Given this limitation, is 8.4 gpm overkill? Or will the increased heating ability compensate somewhat for the decreased water flow?
2. Looks like I need a valve service kit. Are these all the same? They look like they all have threaded fittings to the heater, and then maybe some are sweated v. threaded on the other side. Otherwise I don't see much of a difference. Here are a couple:
Valve 1
(broken link removed to http://www.ebay.com/itm/3-4-Tankless-Water-Heater-Valve-Kit-With-PRV-Sweat-/141393130466?pt=LH_DefaultDomain_0&hash=item20ebaff3e2)
Obviously a big difference in price.
3. Venting. I'll be putting the heater directly below the window, so it will have a short run outside. Doesn't look like a big deal at all to run 2 pipes, and I don't think I have room for the wye if I use one of the concentric kits. But what do I put on the ends of the pipe to make it look pretty/keep varmints out?
4. Final gas hookup--should I use a CSST section? It wouldn't take a ton of work to get iron over to the heater, but it would certainly be easier to use CSST. Depending on how much iron I want to run, it would range from a 48" section needed to 12".
5. Can I use PEX for my supply lines to the valves?

Anything else I'm missing? Parts, especially tough-to-find ones (I know I'll need a gas shutoff, the PVC pipe, some copper and black iron, and that's it?) I've read through quite a bit on this, and a big part of me thinks I'm an idiot to do this rather than just spending $400 on a new traditional tank and calling it a day...

 

[TMonter]

I'm thinking about replacing my 25+ yo 40 gallon heater with a tankless model. Been looking at this one. I currently have 3/4" gas to the old heater (my whole house is I think under-supplied with 3/4" main, but the city keeps on insisting that it isn't...), and 1/2" water. It's vented through a chimney currently, but the location is right next to an inoperable window, which would be a good place for horizontal venting. I have no problems with hot water supply currently. Questions:

1. All the tankless heaters that I've seen specify 3/4" water. I have 1/2" main supply to the house, which is 100 years old and isn't getting changed. Currently no real issues with water pressure. I'm unsure how this will impact the amount of hot water through the heater. Given this limitation, is 8.4 gpm overkill? Or will the increased heating ability compensate somewhat for the decreased water flow?
2. Looks like I need a valve service kit. Are these all the same? They look like they all have threaded fittings to the heater, and then maybe some are sweated v. threaded on the other side. Otherwise I don't see much of a difference. Here are a couple:
Valve 1
(broken link removed to http://www.ebay.com/itm/3-4-Tankless-Water-Heater-Valve-Kit-With-PRV-Sweat-/141393130466?pt=LH_DefaultDomain_0&hash=item20ebaff3e2)
Obviously a big difference in price.
3. Venting. I'll be putting the heater directly below the window, so it will have a short run outside. Doesn't look like a big deal at all to run 2 pipes, and I don't think I have room for the wye if I use one of the concentric kits. But what do I put on the ends of the pipe to make it look pretty/keep varmints out?
4. Final gas hookup--should I use a CSST section? It wouldn't take a ton of work to get iron over to the heater, but it would certainly be easier to use CSST. Depending on how much iron I want to run, it would range from a 48" section needed to 12".
5. Can I use PEX for my supply lines to the valves?

Anything else I'm missing? Parts, especially tough-to-find ones (I know I'll need a gas shutoff, the PVC pipe, some copper and black iron, and that's it?) I've read through quite a bit on this, and a big part of me thinks I'm an idiot to do this rather than just spending $400 on a new traditional tank and calling it a day...

Some other items to consider:

How hard is your water? If you have relatively hard water and no softener for your house, a tankless may be a bad idea. This is one of the primary reasons I chose to abandon a tankless option when I replaced my aging (15 years old and leaking) tank model about 5-6 years ago.

Tankless units can have serious heat exchanger clogging issues with hard water.

What is the efficiency of your current tank model? They do offer some big upgrades with newer tank models with better insulation and much lower stack temps which can be a gain of as much as 20% efficiency. I have a spreadsheet that calculates paybacks and in most instances the additional costs of a tankless unit doesn't payback unless you use a lot of hot water.

How often do you run out of hot water? If the answer is almost never, a tankless might not big a big deal, if you do then it might be a good option.

 

[nola mike]

Some other items to consider:

How hard is your water? If you have relatively hard water and no softener for your house, a tankless may be a bad idea. This is one of the primary reasons I chose to abandon a tankless option when I replaced my aging (15 years old and leaking) tank model about 5-6 years ago.

Tankless units can have serious heat exchanger clogging issues with hard water.

What is the efficiency of your current tank model? They do offer some big upgrades with newer tank models with better insulation and much lower stack temps which can be a gain of as much as 20% efficiency. I have a spreadsheet that calculates paybacks and in most instances the additional costs of a tankless unit doesn't payback unless you use a lot of hot water.

How often do you run out of hot water? If the answer is almost never, a tankless might not big a big deal, if you do then it might be a good option.

The current heater is from 1988. No question, anything will be a significant upgrade. The water is pretty soft, and no, I never run out of hot water. And yup, it's going to take forever to make my money back on this thing. Going by the Energy Star guide, I'll be saving about $100/year over a high efficiency tanked model costing $500 less (more like $600-650, once you factor in additional installation materials). Real life--well, not sure. I'm away from home for significant periods of time. The tankless has a significant advantage then. Otherwise I'm skeptical of the gov't numbers. But over the life of the heater, I'll probably come out ahead. Additional advantages of the tankless, and why I'm doing it: I like high efficiency stuff whenever possible. It saves a ton of space. It's just cool (more of a factor than I'd care to admit).

 

[TMonter]

The current heater is from 1988. No question, anything will be a significant upgrade. The water is pretty soft, and no, I never run out of hot water. And yup, it's going to take forever to make my money back on this thing. Going by the Energy Star guide, I'll be saving about $100/year over a high efficiency tanked model costing $500 less (more like $600-650, once you factor in additional installation materials). Real life--well, not sure. I'm away from home for significant periods of time. The tankless has a significant advantage then. Otherwise I'm skeptical of the gov't numbers. But over the life of the heater, I'll probably come out ahead. Additional advantages of the tankless, and why I'm doing it: I like high efficiency stuff whenever possible. It saves a ton of space. It's just cool (more of a factor than I'd care to admit).

I would think if you're away the tankless only has the big advantage if you don't turn a tank model down when you're gone, but that being said with the soft water and the space savings it may be worthwhile. What else do you have hooked up to gas in the house on the 3/4" gas line?

 

[nola mike]

If I don't turn down the tanked heater you mean. Yeah, the one I have now is a pain to do. Even if it was easier, I probably wouldn't turn it down for the weekend or whatever. Just did some back of the envelope real world calcs--I currently use about 120 therms/year. If I say that a new HE heater is 20% more efficient than the current, and that a HE tankless is another 28% more efficient, it would take me about 10 years payback at current rates of $1.31/therm. The other gas appliances in the house are the furnace (150k i think), stove, and 10k ventless gas stove. And current 40k water heater.

 

[TMonter]

If I don't turn down the tanked heater you mean. Yeah, the one I have now is a pain to do. Even if it was easier, I probably wouldn't turn it down for the weekend or whatever. Just did some back of the envelope real world calcs--I currently use about 120 therms/year. If I say that a new HE heater is 20% more efficient than the current, and that a HE tankless is another 28% more efficient, it would take me about 10 years payback at current rates of $1.31/therm. The other gas appliances in the house are the furnace (150k i think), stove, and 10k ventless gas stove. And current 40k water heater.

With your furnace on the same line I'd check to make sure that the gas line has enough capacity at supply pressure. You don't want to be starving any of the appliances and it wouldn't be uncommon for the furnace and water heater and stove to be going at the same time.

 

[nola mike]

Yeah, I've done the calculations. Even with just my furnace, that's over the capacity of that 3/4" line. I've talked to numerous people at the gas utility, who insist that it's adequate. I'm going to go down to the office with the calculations, and see if I can make some headway. They replaced the meter along with the initial run of pipe into my house a few years ago. Originally I had 1.25" coming in, reduced to one 3/4" and one 1" branch.

 

[jebatty]

Might not be relevant to the tankless heater you are considering, but I had a small electric one for the kitchen (due to long plumbing run) and so long as I ran hot water continuously at a normal to fast rate, worked great. But very poor for off and on and for low flow. Appears that the flow switches did not work to turn on the heat at low flow, and that for off and on operation there would be surges of very hot, then cold, then very hot water, etc.

 

[Rossco]

I have a Navien Condensor 98% efficient tankless unit that's the 'ducks gut's'

100% recommend 3/4 gas & water lines though. He'll my Gas line might be even bigger, I will check when I get home.

100% recommend pro instal as well.

The water around here is nicknamed : 'Muhammed. Am Hard, Bruce lee' and don't have any problems, I do however have it services every two year including a flush.

Well worth it man, when the furnace is off I use around $4 a month in Gas.

 

[Retired Guy]

I looked into tankless heaters and founs that for me, they don't have substantial savings from NG tank type heaters.
http://www.consumerreports.org/cro/...eaters/overview/tankless-water-heaters-ov.htm

 

[nola mike]

I looked into tankless heaters and founs that for me, they don't have substantial savings from NG tank type heaters.
http://www.consumerreports.org/cro/...eaters/overview/tankless-water-heaters-ov.htm

I had read that article in the past. Keep in mind though that it's 6 years old, and the installation costs are a big factor in the payback equations--I'll be doing it myself.

 

[brian89gp]

What about a direct vent tank model?

When you say the 3/4" gas company main, is that before or after the meter? Also as important as your pipe size is your meter size.

 

[CaptSpiff]

Yeah, I've done the calculations. Even with just my furnace, that's over the capacity of that 3/4" line. I've talked to numerous people at the gas utility, who insist that it's adequate. I'm going to go down to the office with the calculations, and see if I can make some headway. They replaced the meter along with the initial run of pipe into my house a few years ago. Originally I had 1.25" coming in, reduced to one 3/4" and one 1" branch.

Can you share your numbers with us? The piping size & run and appliance BTU loads all must fit the tables, be conservative as problems here are not a cheap to re-do.
Putting a 150K furnace with a 160K tankless needs bigger than a 3/4" coming off the meter.
I come off my meter with 1.25" and I only service 220K total, but I run long and I wanted capacity to add appliances. I have 3/4 & 1" drops.
Also, the Utility probably only looking at their Service size and their Meter. The service can appear quite small because it is running higher pressure, stepped down by the regulator, then goes into the meter.
Your piping, starting at the meter is much lower pressure, and therefore needs larger pipe to prevent excessive pressure drop. You probably know that, but this board is read by newbies who may not.

 

[Retired Guy]

I had read that article in the past. Keep in mind though that it's 6 years old, and the installation costs are a big factor in the payback equations--I'll be doing it myself.

I'd seriously consider a hybrid electric/heat pump water heater before installing a tankless. Heat loss in a well insulated tank type heater is not that great.

 

[nola mike]

I've run the tables, and it looks like I'm already inadequate. Like I said, when the gas co replaced the meter, they also replaced the pipes into the house. Going into the meter is 1". Coming out is 3/4". I have 10' of 3/4" before it splits into 1" and 3/4" again, going 25' to my furnace and 30' to WH. The 3/4" continues another 30' to the stove. Also have 20' of 1/2" to a 10k heater. As for a hybrid electric, that's both more expensive and more to operate than either gas option.

 

[eclecticcottage]

We have a Rinnai that came with the place. LOVE it. Not only does it never run out of hot water, but there's no standing pilot and no tank full of water to keep warm. Plus in a less than 700 sq ft house the smaller footprint is a big plus. The only things I don't like about it are the fact that it's power vented (so it uses electric) and if you shut off the water then turn it right back on it bypasses the burner so you get cold water.

 

[nola mike]

I rethought, and think that I'm just going to get a tank model. On closer look, I think I can move the tank back another 2 feet closer to the wall, which will be a significant space savings. I also would get to keep the window that I was planning on venting through. The tankless is just a huge PITA to install and will need a lot of extra parts, plus I still have performance concerns, and I have too many other projects to deal with right now...

 

[Knots]

We have a Rinnai that came with the place. LOVE it. Not only does it never run out of hot water, but there's no standing pilot and no tank full of water to keep warm. Plus in a less than 700 sq ft house the smaller footprint is a big plus. The only things I don't like about it are the fact that it's power vented (so it uses electric) and if you shut off the water then turn it right back on it bypasses the burner so you get cold water.

Agree. I have a Rinnai also. It likes to run or not run. It doesn't like intermittent. I used to wash dishes by hand and rinse them one at a time. Now I use the dishwasher...