Changing out 80gal electric WH to natural gas

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toddyvol

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This is a newly constructed home that I purchased in September. For some reason an electric 80 gal GE water heater with circulating pump was installed. The problem is the high cost electricity and not having enough hot water sometimes. We have 2 showers and a jet tub. If the jet tub is used someone is getting a cold shower.

I did up the thermostat from the factory installed 120 to 140. That has helped a lot with quantity.

Gas is ran to the house for the furnace and can be easily ran to the new WH. I'm wanting to install either the Rinnai RH180 hybrid or Rheem tankless unit.

The current WH is located in an upstairs closet. It would be nice to reclaim that space with a tankless but we do like the current circulating set up and understand we would lose that with a tankless. Thus the Rinnai RH180 would meet both the demand and still be able to circulate.

Any thoughts?
 
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Reach4

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Tankless water heaters take a lot of gas, and your current gas piping may have to be expanded to handle the furnace and tankless/hybrid at the same time.

Tankless gas water heaters do make some sound. They will need vents in the door, unless they get combustion air from outside. That hybrid you named uses a "B vent" which is a conventional hot-gas-rises vent. You might search out other types of venting such as "power vent" and "direct vent" which would not need a roof chimney.

If you do expand your gas piping, you might want to consider making it big enough to handle the new load plus a whole-house generator that you might decide to get in the future.
 

Reach4

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I doubt that a "whole house generator" would be installed in the "upstairs closet".
I was thinking that the gas line all of the way from the meter may need upgrading to handle the furnace and the big on-demand water heater. So I was suggesting that if toddyvol was upgrading the long gas path anyway, he might consider where he might tee off the gas for a future generator.
 

Dana

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The Rinnai RH180 isn't a tankless. It's a small non-condensing tank heater with a modulating ~92K burner, and would be fine with 3/4" gas lines in most installations. It's rated at 180 first hour gallons, but what you're really interested in is it's first 10 minute gallons rating. Filling a tub would almost certainly deplete the tank, so you'd be going on the 92K-in/ ~80K out burner for showering performance.

That's plenty for one endless shower, but really sketchy for two simultaneous showers unless the tank is already hot at the beginning of the showers or you're using the absolute most-miserly low-flow shower heads.

Filling a spa tub with any tankless can take awhile, since they have limited burner capacity. A 50 gallon spa might be filled in 5 minutes with an 80 gallon tank, but could take twice that long or longer even with a 199K burner tankless.

If there is more than 5' of vertical drain downstream of the showers you can get the showering capacity you need out the Rinnai (or even your existing 80 gallon electric) with a 3" x 60" or 4" x 48" or larger drainwater heat exchanger, but it won't do anything for tub fills.

power-pipe-dana-2.jpg



These things pre-heat the incoming water with heat scavenged from the drain, and with a decent sized one it roughly doubles the apparent capacity of the tank in showering mode and shortens the recovery time. But for a tub fill, since the drain isn't running when potable water is flowing there is no heat recovery, so the tank recovery time is on the long side.

A Rheem with anywhere near sufficient capacity would have twice the burner of the Rinnai, and would likely need 1.25" gas plumbing.

Getting the either to run correctly in a closet would take some analysis. There has to be sufficient make-up air for the burner (it's not direct-vent), and there has to be sufficient clearance to the fairly hot (and expensive) stainless Z-venting with any non-condensing tankless. A direct-vented condensing tankless might be easier and often cheaper to install due to the fact that it can use plastic venting, which is a lot less expensive.

Download the installation manuals for any likely prospects and study them carefully for venting and make-up air requirements.
 
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Jadnashua

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Any burner that uses the building's envelope air for combustion, especially a big burner like one required for your anticipated hot water needs would be problematic IMHO. In a closet in the middle of living space (verses say a basement that might have its own air leaks) especially, as you'd almost need a screen door there for proper air intake. Most things require at least 1sqin/1K btu of burner, or 200sqin at the top and bottom of the door. This lets air in, but also will let noises out. Then, keep in mind that the burner will be sucking conditioned air out of the home envelope and sending it out the flue. That is NOT part of the energy efficiency rating on the device. That will pull air from any crack in the house. Much better to go with a sealed combustion device that gets it's air directly from outside. Efficiency ratings are based on the fuel put in verses the usable heat generated, not what may be lost from the conditioned air used to fuel the thing. That can have a major comfort impact when running, not including the energy use to recondition that air sucked into the building.
 

WorthFlorida

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It is obvious that an electric water heater was chosen for it's location. A gas unit with an flame inside the living space that can be burning many hours of the day is not a good idea. If you do your math and call the electric & gas company or look up then on line, there might be information on how much does it cost to run an electric water heater. The gas company more likely would since they would rather see a gas appliance then an electric. The electric may not be that much more than gas. Besides, gas prices can rise pretty fast when supplies suddenly get scarce. The circulation pump saves a lot of water so the hot water is almost instant at the tap. With an instant hot unit your water bill will go up.

Your real problem is the jet tub, that is why an 80 gallon unit was installed. If you have the jet tub filling with water, one or two showers running and someone turns on the dishwasher, the instant hot may not be able to meet the demand either. While the instant hot (gas unit) is making hot water the efficiency drops. The savings come from the off time not having to keep 80 gallon warm 24/7. With the heater at 140 degrees you should install a water heater tempering valve. Look it up on line. Pic's and info everywhere. At 140 degree someone can be scolded in only 5 seconds for a third degree burn. http://burnprevention.org/scald-prevention/

Instant hot units can fail and leak, a co-worker had a fitting fail and flooded his house (when no one was home). The 80 gallon unit is probably has a pan under it and maybe a drain. With an instant hot hanging on the wall you do not have it. Check the manufacturer spec on the required space around the unit to access it for servicing. If the closet is kind of small it could be a problem. Then you better check you local building department if a gas unit can be installed in a closet, direct vent or not. There could some restrictions.

My brother has a very large home in VT and has a instant hot for domestic water (very cold well water) and for home heating. It works quite well and does the job. I do not know what brand or size it is but it is vented directly out the wall for air and exhaust venting and it is located on the basement/garage level.

If you really want to convert to gas the heater should be relocated to the garage or basement if you have one. If your 80 gal heater was in the garage there hardly be a problem.
 

toddyvol

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It is obvious that an electric water heater was chosen for it's location. A gas unit with an flame inside the living space that can be burning many hours of the day is not a good idea. If you do your math and call the electric & gas company or look up then on line, there might be information on how much does it cost to run an electric water heater. The gas company more likely would since they would rather see a gas appliance then an electric. The electric may not be that much more than gas. Besides, gas prices can rise pretty fast when supplies suddenly get scarce. The circulation pump saves a lot of water so the hot water is almost instant at the tap. With an instant hot unit your water bill will go up.

Your real problem is the jet tub, that is why an 80 gallon unit was installed. If you have the jet tub filling with water, one or two showers running and someone turns on the dishwasher, the instant hot may not be able to meet the demand either. While the instant hot (gas unit) is making hot water the efficiency drops. The savings come from the off time not having to keep 80 gallon warm 24/7. With the heater at 140 degrees you should install a water heater tempering valve. Look it up on line. Pic's and info everywhere. At 140 degree someone can be scolded in only 5 seconds for a third degree burn. http://burnprevention.org/scald-prevention/

Instant hot units can fail and leak, a co-worker had a fitting fail and flooded his house (when no one was home). The 80 gallon unit is probably has a pan under it and maybe a drain. With an instant hot hanging on the wall you do not have it. Check the manufacturer spec on the required space around the unit to access it for servicing. If the closet is kind of small it could be a problem. Then you better check you local building department if a gas unit can be installed in a closet, direct vent or not. There could some restrictions.

My brother has a very large home in VT and has a instant hot for domestic water (very cold well water) and for home heating. It works quite well and does the job. I do not know what brand or size it is but it is vented directly out the wall for air and exhaust venting and it is located on the basement/garage level.

If you really want to convert to gas the heater should be relocated to the garage or basement if you have one. If your 80 gal heater was in the garage there hardly be a problem.


According to the manufacturer, the Rinnai RH180 clearances requires 12"top, 4"front, & 0" sides. The closet is fairly large, large enough to fit the current 80gal that's 23" wide and about 48" wide. The closet is also vented overhead to the adjacent room and there is a pan and drain under the current WH. Municipal code states "Water heaters and storage tanks shall be located and connected so as to provide access for observation, maintenance, servicing and replacement." The two garage is very cramped for space and a tank wouldn't work. There is no basement. The gas furnace is located in the attic above the garage and is accessed through a knee wall door from a bedroom closet. It is possible to move a new smaller tankless WH to that area but not enough room for tank. I had considered doing that but was kinda wanting to keep the circulating system. If I moved it to the attic area it would also be farther from the main bath.

Is there a good reasonable priced tankless that circulates that would meets our needs?
 

Jadnashua

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What is the worst-case, winter-time cold water inlet temperatures? That number will determine, along with the flow volume of the filler for the tub and any other concurrent users, how much temperature rise is required and thus the size of the unit needed to satisfy you. I suggest you read the tankless tutorial I put into the Tutorial section. Where I live, installing a tankless would not work in the winter to fill my 6' tub unless I wanted to buy two of them. Since one was already more than I wanted to spend, two of them just wasn't an option!

A good tub filler valve can flow upwards of 10gpm. Throw in a couple of people wanting to shower at 2.5gpm each, and you need to be able to heat 15gpm. Think about that...if you had a 15g pot and put it on the stove, how long would it take to heat it to showering temp or hot enough for a bath. Now, think about doing that repeatedly every minute...it takes a BIG burner. Much less stressful to have hours to heat it up and put it into a tank, but it must be sized appropriately. Then, you have most of the day for it to recover, rather than having to do it constantly during use.
 

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Even with 45F incoming water (probably about the low-temp in winter in Athens TN) that's a 60F rise to the ~105F at the shower head. A couple of simultaneous 2 gpm showers would take 125,000 BTU/hr of condensing tankless burner. A 199.9K burner would then have about 2.5gpm of capacity for everything else.

At a 70F rise (say 40F in, 110F out) a 199K burner can only deliver a bit over 5 gpm for filling tubs. A 50 gallon soaker tub would take ~10 minutes, a 75 gallon spa ~15. It'll never run out of hot water, but for filling big tubs a big tank is usually the better solution. If you wanted to gang together a PAIR of 199K tankless (and have the gas service that can actually support that much burner), you can get the fill times for big tubs into the sorta-reasonable range. Filling any tub bigger than 50 gallons with a tankless would be an exercise in tedium.
 

Jadnashua

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The hassle is, many tub/shower valves do not have a volume control, so once on, it gets whatever volume the pipes can supply. If it's faster than the tankless wants for the set temp rise, one of two things will happen: the tankless will throttle the volume (not all can do this), or the outlet temperature will drop proportional to the flow volume. With a tank, things stay relatively constant until you near the end of the tank since they are filled from the bottom, either via a dip tube on the top, or literally from the bottom (less common), and while you get some mixing, you don't get all that much. Especially with an electric, it would have switched on the top heating element which will keep the water warmer. A gas WH doesn't have that ability...it always heats mostly from the bottom (some via the flue), but still would have the inlet water going to the bottom. It's also not all that uncommon for a single-handle valve to not be setup for all hot, and always would have some mixing. Most do have a means to adjust that internally, but the factory default assumes 120-degree hot and a nominal 105-degree outlet, so will always add some cold. A dishwasher typically wants warmer water, some applications on a washing machine might as well, and that's 105 at the shower - there will be some temperature drop from the heating unit to the showerhead, so you need to start with it hotter unless the heater is right next to the shower or tub. Hard to do if there's multiple user points. ANd, you'll get lower volume if you use only hot...mixing in some cold give the system the ability to use the combined capacity of both supplies.
 

toddyvol

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What's the fill volume of the tub?

If my calculations are correct, it's about 140 gallons filled to the brim. Actual fill is probably 75 gallons or so. The first hour rating on the current electric WH is 83gal. The Rinnai RH180N is 180 gallons FHR.
 

Dana

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The key factor is the first 10 minute rating.

The 80 gallon HW heater at storage temp of 140F can probably deliver the 75 gallons of 110F water in 6-7 minutes, but I doubt very much that the Rinnai can. The storage volume on the Rinnai is 40 gallons, so it won't fill the tub quickly. You won't get more than ~55-60 gallons of 110F water out of it in the first 5 minutes after which it becomes burner-constrained. At a 70F rise & 80,000 BTU/hr of burner output you'd be dribbling about 2.3 gpm for the remaining 15-20 gallons, which will seem like an eternity. So what if it can still dribble 2.3 gpm for the next 55 minutes to hit it's first-hour numbers? That's one shower at best, and since there's nothing left in the tank after a tub fill it can't support two simultaneous showers rigth after a tub fill, not even for 1 minute.

If it fits, an 80 gallon Phoenix Light Duty gas-fired HW heater would probably prove satisfactory. It'll fill the tub at least as fast as your 80 gallon electric did, and with a 76K condensing burner you'd have horsepower to spare for covering a single shower even DURING the tub fill. (The "Light Duty" is only relative to commercial hot water heating.) It's more expensive than a 199K tankless or the Rinnai hybrid, but it'll serve your hot water needs better. With a higher storage temp there would be enough to support two showers for several minutes after a tub fill before it starts to fade. If give it a 10 minute head start for recovery it would support two showers for quite awhile. In conjunction with drainwater heat recovery unit you could run two showers even during the tub fill.

An 80 gallon Rheem Spider Fire with the 130K burner is more expensive than the Phoenix Light Duty (thinking of spending 4-5 grand on a water heater?), but has you covered hands-down.

There are other cheaper 75-80 gallon commercial gas hot water heaters with less sophisticated controls that would work too. If it's an 80% efficiency unit you'd need at least 90-100 BTU/hr of burner to really do it, with condensing burners 75-80K is enough. The Phoenix is a stainless tank which should be good for a couple of decades or more. A cheap glass-lined commercial HW heater is good for maybe 10.

Keeping the 80 gallon electric where it is and plumbing a 150-199K tankless in series with it might also get you there. As long as the tankless was feeding only the electric tank you could crank up the output temp of the tankless to something ridiculous (=dangerous), and it could work out OK. It's a bit of a hack and would have to be considered more carefully before going that route, but it's not impossible. During a tub fill the tank temp would go down a bit, but as long as it stayed above showering temp the tankless would cover a 2-shower load.
 

WorthFlorida

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Here is a small article from consumers reports but it is dated 2008. Tankless models may have improved. You might be getting stuck between a rock and a hard place. Do you want to have more hot water for your demands, reduce the utility bill, or be green? To get all three solar would be the way to go but it also has its own requirements, a storage tank, controls, south face roof and big $$$$. This forum also has a "tankless" section and if you scan through the posts, tankless have there own unique problems and maintenance requirements. I would at least wait until September to get a 12 month read on your electric bills. Then do the math to determine if your really saving that much vs the install costs of a tankless.

My brother's home uses a propane tankless unit to heat a 30 or 40 gal storage tank. It provides consistent temperature for the hot water demands because the tankless also provides hot water for heating the home where the output temperature needs to be very hot. It's more money because you need controls to turn on a circulating pump to heat the water tank but and you can still keep the circulating system for the faucets. But if want to go gas and as Dana suggests, use the tankless to supplement the electric heater

When the wife and I went house hunting, there were many homes with two electric water heaters and almost always it was to meet the demand of those big Jacuzzi type tubs.
http://www.consumerreports.org/cro/...eaters/overview/tankless-water-heaters-ov.htm
 

Master Plumber Mark

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They dont make 80 gallon electric water heaters any longer so some day you will have
to make the big decision about what to do....before I threw a tankless into my upstairs
closet I would look for alternatives to doing this..

all these big time "tankless advisors" here on terrys site have failed to mention
that you need to have very soft water to maintain that tankless heater....
and they need to be de-limes at least once a year or your warranty
could be voided......so do you have a water softener???

Rheem makes a life time marathon electric water heater that is 85 gallons..
if you had another space elsewhere like in the garage, perhaps a 75 gallon power vent might
be another option....

before you drink the cool aide that these "tankless gurus" are handing out ,
I suggest you think long and
hard about what you are getting yourself into.... .
 

toddyvol

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They dont make 80 gallon electric water heaters any longer so some day you will have
to make the big decision about what to do....before I threw a tankless into my upstairs
closet I would look for alternatives to doing this..

all these big time "tankless advisors" here on terrys site have failed to mention
that you need to have very soft water to maintain that tankless heater....
and they need to be de-limes at least once a year or your warranty
could be voided......so do you have a water softener???

Rheem makes a life time marathon electric water heater that is 85 gallons..
if you had another space elsewhere like in the garage, perhaps a 75 gallon power vent might
be another option....

before you drink the cool aide that these "tankless gurus" are handing out ,
I suggest you think long and
hard about what you are getting yourself into.... .
I do not have a water softener but am prepared to do yearly maintainance. I guess what drew me to the Hybrid Rinnai RH180 is that I thought it being a tankless mounted on the side of a tank, that would help solve my problems. It claims to provide continuous hot water. The tub we have is used maybe once a week. Our biggest problems are the 3 showers back to back and the high cost of electricity. We usually have enough hot water for 3 showers but the last person can start feeling the water getting a little cool. If the tub is filled then two showers after would either need to wait or the second shower will get cold.
 

Master Plumber Mark

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I do not have a water softener but am prepared to do yearly maintainance. I guess what drew me to the Hybrid Rinnai RH180 is that I thought it being a tankless mounted on the side of a tank, that would help solve my problems. It claims to provide continuous hot water. The tub we have is used maybe once a week. Our biggest problems are the 3 showers back to back and the high cost of electricity. We usually have enough hot water for 3 showers but the last person can start feeling the water getting a little cool. If the tub is filled then two showers after would either need to wait or the second shower will get cold.

just remember that the yearly maintenance on the tankless heaters is not cheap.
In our town they are chargeing between 250--300 bucks to come out and spend about an hour and a
half pumping vinegar through the unit....

If you are gonna have someone de-lime the tankless then the cost of de-limeing it will
outstrip the savings over just living with the electric heater...

Of course if you are gonna de-lime it yourself...then its not a big issue...but most folks shy away from doing this themselves....

ALL " The tankless gurus " on this site will tell you how easy it is to do this....and alsohow easy it is to put in a recirulation line in for the tankless ect ect...

tweaking these things is not all that much fun.....

its a catch 22
 

JerryR

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Nobody so far mentioned a tempering valve at the water heater. This won't solve the cost of electric vs gas but it should go a long way to solve the capacity issue.

Installing a tempering valve at the heater you can inexpensively turn your 80 gallon water heater capacity into an equivalent 120+ gallon water heater.

That solved my issue filling my garden tub without running out of hot water.
 

Master Plumber Mark

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Nobody so far mentioned a tempering valve at the water heater. This won't solve the cost of electric vs gas but it should go a long way to solve the capacity issue.

Installing a tempering valve at the heater you can inexpensively turn your 80 gallon water heater capacity into an equivalent 120+ gallon water heater.

That solved my issue filling my garden tub without running out of hot water.

actually that is probably the best idea mentioned so far..... cudos to you sir :D:D

. as long as you have a thermal expansion
tank on the heater and a pan and a drain for the t+p valve
that is probably the best route you could go..... with the present 80 gal unit

crank it up to 150 and temper it down.... Install a water heater blanket on the unit
and really capture the most you can out of it.........

the only problem with this is the fellow sounds like a " tight wad" and is worrying about the
economic expence of running that heater on extra hot.......

it dont make any sense to me to throw money into a tankless thinking you are saving big
bucks over a normal heater.... its all in their own minds.......
 
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