Tankless or Stainless to upgrade from 50G NG?

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Hello,

We currently have a 12-year old 50G natural gas water heater that is still working, but performing less week than before.

We have been considering replacing it for improved performance, and would love advice from this knowledgeable community. The main reasons for the upgrade are: a big 98 gallon tub we don't really use since we can't fill it with hot water (my wife has mentioned this to me for 12 years) and two young daughters who will be teenagers soon and I anticipate the need for more hot water for our family of four to maintain happiness during morning getting-ready routines.

Cost is not a huge issue, as we are thinking this is more a long-term investment for better performance over our lives in this house. There is though a limitation on size - the space for the water heater is about 26" wide and 29" deep. Current water heater is about 57" tall and fits with no problems, but the space prevents us from going to a 75 or 100g conventional WH. There's a bit more leeway space above it for venting, pipes, and an existing recirculation pump, so a new one could be a little taller. Our home does have a NG stove, furnace, dryer, and fireplace (rarely used), and have no tmeasured the output at the 1/2" valve near the existing WH so don't yet know what it could handle. The gas meter is about 25' feet from the WH so we could run a dedicated, larger pipe without a huge amount of trouble beyond the cost.

A few things I have been considering:

(1) An a thermostatic mixing valve - we've already turned up the temp of the existing WH, but this might allow us to turn it up more while maintaining safety - since our current WH is still working. Should be pretty inexpensive to have a plumber do this but how effective?

(2) Replace existing with a new 50g, but newer one. It'd have same performance specs but perhaps be a bit better since it's newer and would have no deposits. This seems relatively cheap to do plus would come with the mixing valve.

(3) Replace with 11.1GPM tankless. This will be expensive since it requires different venting as well as likely a more robust gas line routed directly to the tankless. Benefits are infinite hot water, but I've read about the many drawbacks and complaints of tankless (flow rate, maintenance, descaling, noise of unit, noise of pipes) so not sure if that's a good idea. It would be nice to have the space back in the garage since our garage is small.

(4) Replace with stainless commercial. I've just learned through reading on this form that this may Be an option but don't know too much about them. Apparently they would have higher BTU capabilities so they could be comparable to size of my existing water heater but perform much better (e.g., better recovery rate, low maintenance)? It sounds like then I'd still need an upgraded gas line. Are most installers familiar with installing stainless? None I've talked to have suggested them. Can a commercial unit be installed in residential? Any other drawbacks or concerns, beyond cost?

I would welcome hearing any recommendations you have. Thank you for your help!

 

[Jadnashua]

1. With a 12-year old unit, I'd not spend the money to have a mixing valve installed on it...save that hardware and labor cost for replacing the tank.
2. There are higher output burners than the more common sizes. THey might require an upgraded flue. Unless you get a unit designed for closed combustion (it gets its combustion air from outside), your space may not be large enough to support a much larger burner. Keep in mind that the O2 used for the burner is coming from the inside of your house, and it must be replaced. That typically comes from leaks...so, you're exhausting air you've conditioned, sucking in unconditioned air, and sending it out the flue. A closed combustion unit gets its air from outside...much more efficient overall. There's a general rule of 1sqin of area for each 1K BTU of burner required, and the volume of the area needs to be a certain size based on the BTU...this is all a mute point if you get a closed combustion unit, as long as your intake pipe and effective distances are within specs.
3. Depending on where you live, and your incoming water temperature, you may not be able to achieve that flow rate. Most of them are rated with a 50-degree inlet water temperature. For every degree lower, you either get a degree lower output, or a lower volume as it moves that colder water past the heat exchanger. For one that can do that volume, you certainly will need a larger gas supply line, and maybe even a larger gas meter and line from the street! That depends somewhat on the gas pressure before the regulator and the actual meter involved. Note, in many places, even though you may not actually use more gas, your base charge is determined by the maximum capacity...IOW, because when you actually are using the thing, your demand from the mains will be quite high, they bill you extra based on that even if it's only used occasionally.
4. A commercial unit doesn't necessarily mean it has a stainless steel tank...it is designed for a higher utilization rate, often a larger burner, and also, usually, a shorter warranty verses a typical residential unit.

 

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[adjacent]

1. With a 12-year old unit, I'd not spend the money to have a mixing valve installed on it...save that hardware and labor cost for replacing the tank.
2. There are higher output burners than the more common sizes. THey might require an upgraded flue. Unless you get a unit designed for closed combustion (it gets its combustion air from outside), your space may not be large enough to support a much larger burner. Keep in mind that the O2 used for the burner is coming from the inside of your house, and it must be replaced. That typically comes from leaks...so, you're exhausting air you've conditioned, sucking in unconditioned air, and sending it out the flue. A closed combustion unit gets its air from outside...much more efficient overall. There's a general rule of 1sqin of area for each 1K BTU of burner required, and the volume of the area needs to be a certain size based on the BTU...this is all a mute point if you get a closed combustion unit, as long as your intake pipe and effective distances are within specs.
3. Depending on where you live, and your incoming water temperature, you may not be able to achieve that flow rate. Most of them are rated with a 50-degree inlet water temperature. For every degree lower, you either get a degree lower output, or a lower volume as it moves that colder water past the heat exchanger. For one that can do that volume, you certainly will need a larger gas supply line, and maybe even a larger gas meter and line from the street! That depends somewhat on the gas pressure before the regulator and the actual meter involved. Note, in many places, even though you may not actually use more gas, your base charge is determined by the maximum capacity...IOW, because when you actually are using the thing, your demand from the mains will be quite high, they bill you extra based on that even if it's only used occasionally.
4. A commercial unit doesn't necessarily mean it has a stainless steel tank...it is designed for a higher utilization rate, often a larger burner, and also, usually, a shorter warranty verses a typical residential unit.

@jadnashua Thank you for the reply!

Re: #2 - I believe I currently have a 3" B-vent that exits up through the roof. Larger BTU units I believe would need a 4" vent. I'm not sure if it means replacing the entire 3" B-vent to 4" (which would be costly and laborious to do) or if it's possible to vent through the side of the house. The current water heater sits inside the garage right next to the outer wall of the house, so it wouldn't necessarily be too hard to do, though I think I've heard there is a minimum venting length, in addition to a max length.

Re: #3 - I live in the Bay Area, but I don't know what the normal water temp is during the seasons. I didn't realize that the larger gas line (say, a 3/4" or 1") might require a larger gas meter or even a larger line from street to meter. That makes sense though.

Re: #4 - Did you have any thoughts on stainless units (such as the Phoenix/Westinghouse)? It sounds like they could provide better performance in a similar size footprint, though would also require a new vent (in and out) and also a bigger gas line.

Perhaps given the limitations on size, vent, and gas that I have, it makes the most sense to just stick with a conventional 50g NG water heater with a mixing valve, whenever my current one dies.

I'd love to hear any more thoughts folks have about this or other options (tankless, stainless, or perhaps even a point-of-service heater just for the big bathtub - though that would need to be electric, so likely not sufficient), and what they might recommend. Thanks again!

 

[Dana]

Codes typically require a mixing valve or tempering valve betwe

ng this is more a long-term investment for better performance over our lives in this house. There is though a limitation on size - the space for the water heater is about 26" wide and 29" deep. Current water heater is about 57" tall and fits with no problems, but the space prevents us from going to a 75 or 100g conventional WH. There's a bit more leeway space above it for venting, pipes, and an existing recirculation pump, so a new one could be a little taller. Our home does have a NG stove, furnace, dryer, and fireplace (rarely used), and have no tmeasured the output at the 1/2" valve near the existing WH so don't yet know what it could handle. The gas meter is about 25' feet from the WH so we could run a dedicated, larger pipe without a huge amount of trouble beyond the cost.

A few things I have been considering:

(1) An a thermostatic mixing valve - we've already turned up the temp of the existing WH, but this might allow us to turn it up more while maintaining safety - since our current WH is still working. Should be pretty inexpensive to have a plumber do this but how effective?

(2) Replace existing with a new 50g, but newer one. It'd have same performance specs but perhaps be a bit better since it's newer and would have no deposits. This seems relatively cheap to do plus would come with the mixing valve.

en any water heating equipment and hot water distribution pluming that goes to sinks & bathing (but not clothes & dishwashing equipment). Installing a mixing valve now means you won't have to install one later. As long as the mixing valve is far enough away from the existing unit to allow space for a possibly taller tank, it won't even have to be moved when it's time to replace the tank.

The 76KBTU/hr burner Phoenix Light Duty doesn't usually need a new gas line, even 100K burners versions don't usually need a gas line upgrade. A half-inch valve is pretty short in terms of "equivalent feet", and most 50 gallon gas-burners were plumbed in with 3/4" gas plumbing. Unless someone went out of their way to plumb it all the way with half-inch (I've haven't seen that recently, but that doesn't mean it can't happen) you're probably going to be fine.

Any condensing equipment will need a new vent, but plastic venting is dirt-cheap.

The diameter of a Phoenix Light Duty (and the Westinghouse equivalent) is 23" , but the full depth of the side with the burner is 32.5", violating your 29" depth constraint by a few inches. If you can deal with that and the 69" height of the PH76-80 (the 80 gallon version), it would be a pretty reasonable choice.

Bay Area incoming water temps only rarely, if ever, drop as low as 50F. (The annual average is in the mid to high 60s.) Mixing 80 gallons of 140F water with 40 gallons of 50F water yields 120 gallons of 110F water (about right for a tub-fill). There is some discounting of the volume for stratification, but you should be able to just fill a 98 gallon tub even in the dead of winter. But with a 50 gallon tank even with 65F incoming water it isn't going to make it, unless the storage temp is substantially higher than 140F- even 160F might not cut it in winter.

 

[Jadnashua]

A tankless that can get you over 11gpm will require larger gas lines. To get that you'll need one or maybe two 199K BTU units, and that's a lot of fire power. A tank-type WH usually wouldn't stress a typical install's line capacity. IT takes a larger burner to 'instantly' raise the temperature...it's lots easier with a tank that acts like a big buffer...unless, you have extended, continuous needs of hot water (say, a commercial laundry, a big restaurant kitchen, or maybe a spa); the tank can take its merry time to reheat...the key is to have enough in the tank and burner to keep it hot for your intended use that is often sporadic, but may be intense for awhile.

 

[adjacent]

@Dana and @jadnashua - thank you for the insights!

It sounds like a tempering valve can be helpful to my current situation, and since it's now required, if installed high enough, would be used for any future water heater I install.

It also sounds like tankless is not the way to go, for a variety of reasons, not least of which is the gas needs.

The three best options on a new WH seem to be:

(1) New conventional 50g tank, which would come with a tempering valve - will have slightly better performance than current set up since it's new and has tempering valve, but wouldn't be enough to fill tub

(2) Stainless 80g tank - this will have much better performance (better FHR and recovery than current and option #1), and with the tempering valve could allow the full fill of a 98 gallon bath tub. But though I think the space could accommodate the extra few inches in width, not sure about the extra foot of height.

(3) Stainless 50g or 60g tank - this would also have better performance than current/opt #1, but even with tempering valve couldn't fill the tub.

Does that seem right?

A few more questions:

(a) Is there a need to add an expansion tank when adding a mixing valve to accommodate for thermal expansion given the WH would be set at a higher temp?

(b) Is there a way to confirm the water column of my gas valve prior to install, to ensure we have enough gas? I assume I'd need to have it measured while turning on other gas appliances too (e.g., stove, furnace, fireplace, dryer).

(c) The vent for the stainless seems pretty straightforward. Would it be one new hole cut into the side wall for the in/out vents and one new small hole for the condensate? Does the vent need to be a minimum length? Does the condensate need to be neutralized if it's going outside? I know my installer should know all these, but I just like to be informed as well.

(d) My current setup has an external recirculation pump. I assume it'd work fine with the stainless, but wanted to confirm.

(e) For option #3, given the better FHR and recovery, would that be enough to accommodate more showers (either 2 at the same time or multiple back-to-back-to-back)? I know it wouldn't fill the tub, but wanted to see how much better it might be than option #1.

(f) Overall, it sounds like the 80g stainless may be the best option if we really want to fill the tub. Interestingly, of the many local plumbers/vendors I've talked to, none of them are experienced in installing stainless. Is that because they are tied to the brands they promote? How could I find an installer experienced in these? I have noticed that Westinghouses are sold through the orange major chain, but not sure if that is a good way to go.

(g) Are there any downsides to stainless, beyond higher cost? Any issues with noise or maintenance or other issues?

Thanks again for folks helping me learn and figure out good solutions. Very much appreciated.

 

[Dana]

SFAIK water heaters don't come with tempering valves or thermostatic mixing valves- it's always plumbed separately. I'm not sure how high you can set the temperature on the Phoenix LD, but I'm sure it's nowhere near 160F (or else you wouldn't be able to use plastic venting), so it takes the 80 gallon (77 gallons, actually) version to fill a 98 gallon tub with it. Condensing water heating equipment rarely goes over 140F by very much. (Codes often require a 140F storage temperature for legionella mitigation.) Non-condensing heaters can sometimes be run as high as 180F, but it may need to be special ordered to have controls that operate that high.

Stainless tanks are fine to use with recirculation pumps, etc. Stainless tanks will usually last at least 2x as long as a typical glass lined water heater, warranty period details notwithstanding.

The Westinghouse version is identical to the HTP version, but it's a different support organization. I've never had to deal with them, don't know if it's good or bad (and it may vary by region/location anyway.)

I don't believe there is a minimum length requirement for the venting, but there is a maximum, Take a peek at the installation manual for details.

 

[adjacent]

Thanks @Dana.

Yes, I meant that the tempering/thermostatic mixing valve would be added as another part of the installation.

I should be able to locate the HTP version as well. It sounds like you've had good experience with it and like their product.

For the venting, would it need an exterior intake? The water heater is in a 2-car garage. I'm not sure if that's enough for atmospheric venting like the conventional WH is, or if it needs something more.

I'll take a look at the installation manual too.

Thanks again.

 

[Dana]

HTP's headquarters are less than an hour's drive away. Local scuttlebutt has it that HTP support is good in my area, but YMMV. (I've personally never had to use HTP's support, but I'm not in the biz, so the sample size is small.) I would expect that between mega-corp Westinghouse and mega-corp Home Depot you would get at least adequate support for a Westinghouse version purchased through Home Depot, but I don't have any datapoints to indicate whether that is in fact the case.

Garages are usually air-leaky enough to provide makeup air even for atmosphreric drafted systems, but garage air is often dustier/dirtier than outdoor air. Like all condensing water heaters the Phoenix LD is power drafted, so the make-up air issue isn't a big deal, but piping in outdoor air per the manual removes all question. IIRC with this unit you're allowed up to 150' (combined) intake + exhaust vent length (with the "equivalent lengths" of all ells & tees added in, of course), but it's in the manual.

 

[adjacent]

SFAIK water heaters don't come with tempering valves or thermostatic mixing valves- it's always plumbed separately. I'm not sure how high you can set the temperature on the Phoenix LD, but I'm sure it's nowhere near 160F (or else you wouldn't be able to use plastic venting), so it takes the 80 gallon (77 gallons, actually) version to fill a 98 gallon tub with it. Condensing water heating equipment rarely goes over 140F by very much. (Codes often require a 140F storage temperature for legionella mitigation.) Non-condensing heaters can sometimes be run as high as 180F, but it may need to be special ordered to have controls that operate that high.

Stainless tanks are fine to use with recirculation pumps, etc. Stainless tanks will usually last at least 2x as long as a typical glass lined water heater, warranty period details notwithstanding.

The Westinghouse version is identical to the HTP version, but it's a different support organization. I've never had to deal with them, don't know if it's good or bad (and it may vary by region/location anyway.)

I don't believe there is a minimum length requirement for the venting, but there is a maximum, Take a peek at the installation manual for details.

HTP's headquarters are less than an hour's drive away. Local scuttlebutt has it that HTP support is good in my area, but YMMV. (I've personally never had to use HTP's support, but I'm not in the biz, so the sample size is small.) I would expect that between mega-corp Westinghouse and mega-corp Home Depot you would get at least adequate support for a Westinghouse version purchased through Home Depot, but I don't have any datapoints to indicate whether that is in fact the case.

Garages are usually air-leaky enough to provide makeup air even for atmosphreric drafted systems, but garage air is often dustier/dirtier than outdoor air. Like all condensing water heaters the Phoenix LD is power drafted, so the make-up air issue isn't a big deal, but piping in outdoor air per the manual removes all question. IIRC with this unit you're allowed up to 150' (combined) intake + exhaust vent length (with the "equivalent lengths" of all ells & tees added in, of course), but it's in the manual.

Thanks again, @Dana. That makes sense about the mega-corp support and about the intake. In the manual, I saw an option to do a concentric vent, which seems preferable as it would only mean one hole in the wall and one vent to look at. I've heard that there may be a stainless steel endcap one can put over the PVC, purely for aesthetic reasons. Any experience with that?

 

[Dana]

I have no direct with installing one of these, concentric or separate, with or without stainless terminators, but there's no reason to suspect that it's a problem. It's a much smaller burner than a tankless.

 

[Jadnashua]

I have a condensing boiler...while it uses pvc pipe for the intake and exhaust, the exterior vent is made of SS...as long as it's the proper size and installed properly it should work. FWIW, when they initially installed mine, they had the vent lines 180-degrees out...on a particularly cold stretch in the winter, whatever moisture was left in the system iced over the intake. This was not installed per the manufacturer's installation instructions, and they flipped it after a little repiping, and it's worked fine since. LIke anything...you need to follow the instructions for best performance. Many of the condensing furnaces in my condo use a plastic vent hood that has been painted the siding color, and those are holding up well after a number of years. Both of these 'look' like a single piece, but there's a baffle in between the intake and exhaust along with a hood to keep the two air streams from mixing.

 

[adjacent]

I have a condensing boiler...while it uses pvc pipe for the intake and exhaust, the exterior vent is made of SS...as long as it's the proper size and installed properly it should work. FWIW, when they initially installed mine, they had the vent lines 180-degrees out...on a particularly cold stretch in the winter, whatever moisture was left in the system iced over the intake. This was not installed per the manufacturer's installation instructions, and they flipped it after a little repiping, and it's worked fine since. LIke anything...you need to follow the instructions for best performance. Many of the condensing furnaces in my condo use a plastic vent hood that has been painted the siding color, and those are holding up well after a number of years. Both of these 'look' like a single piece, but there's a baffle in between the intake and exhaust along with a hood to keep the two air streams from mixing.

Thanks, this is helpful. A plastic vent hood painted to the same color as the exterior of the house would probably be fine.

How far do the vent hoods protrude from the exterior wall? I've seen some that are close, but also so that extend out 12" or more.

 

[Jadnashua]

The ones on the Trane furnace stick out probably about 4"...my SS one for my boiler is about the same. The ones on the Tranes look pretty much like this one

 

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The ones on the Trane furnace stick out probably about 4"...my SS one for my boiler is about the same. The ones on the Tranes look pretty much like this oneView attachment 41562

An HTP video I watched about the Phoenix light duty mentioned that too much humidity in the intake valve can be bad for the unit. I live in an area that can have lots of fog, so a lot of moisture in the external air. I wanted to see if folks had thoughts about that. Previously, it sounded like atmospheric intake via garage air might be sufficient but to might as well do external air. But if the external air can often be moist, would it be better to do atmospheric air from inside the garage?

 

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Curious also if anyone has experience with how loud the Phoenix Light Duty water heater is. It will be in my garage, but in a corner that has an exterior wall and an interior wall. I've heard that it may be loud and cause vibration, due to the power vent.

 

[cecil1966]

I just installed tankless heater and very impressed with it. For a family of 4, and convenient place to install, I would highly recommend tankless.

 

[adjacent]

After spending more time talking to plumbers and installers, I am leaning away from the stainless steel units. No doubt that they'd provide the best performance and hot water - and another plus is not needing a new gas line unlike a tankless. However, the installation is still tricky (requiring a new vent as well as a condensate line), the power vent can be loud (the WH location is in garage but near an interior wall), and though the stainless tank lasts a long time, I've heard there can be more maintenance issues over a conventional WH. And of course there's the cost. All those uncertainties may not be worth it just to have a luxury bath. So I'm thinking now just a new conventional WH with a tempering valve and expansion tank.

Would still love to hear thoughts from folks before I proceed with anything. Thanks!

 

[Jadnashua]

IF the tank is sized properly, you should be able to fill the tub without issues. Today's tanks are more efficient because regulations forced them to add insulation to pass, which saves energy and doesn't really add much to the initial purchase. The second part of the regs is the redesign of the burner to prevent flammable vapors (from the idiots that stored things like paint thinner, gasoline, etc. near the WH) from causing an explosion. The combination of those two things make the tanks a bit taller and cost more.

 

[Dana]

A modulating-burner stainless tank like the Phoenix LD is no louder than a tankless- quieter than most due to the smaller burner size. It's quite a bit different from inexpensive non condensing residential power vented units, where the vent blower is a cheap noisy thing comparable to or louder than a large hair dryer.

Starting at about 5.00 in this technician training video they fire the thing up and run it at all blower speeds while checking & adjusting the combustion mixture, etc. The thing is quieter than the Takagi tankless in my basement.