To go tankess or not

[Eden]

When we bought our house 20 some odd years ago we figured we'd go tankless when we had to replace our aged and limping electric 50 gallon hot water heater, but lo and behold with a few minor repairs, it's held out all these years.... Now we've got our soaking tub in place we're once again considering the change, but a little closer look makes me wonder whether or not it's a good idea.

We have gas into the house and a few years ago when we had to have the furnace replaced we had a stub put in place for the eventuality of a gas tankless water heater too.

The particulars

There are only two of us in the house and we don't have super high water usage. It's highly unlikely we would have one person running a bath and another wanting to shower at the same time, same goes for laundry, dishes etc.

Our current hot water heater is an electric 50 gallon.

Our heater is a gas force air furnace and it has a condenser and pump that the water heater could be tied into.

We live in Seattle and the city water is very good and pretty soft.

In Seattle electricity is pretty cheap because of all of our hydro. We currently use a timer on the water heater so that it only heats in the morning and evening or if we turn it on, so we know it might not mean much energy savings, but might it actually be more to use the tankless than our current setup?

We do have a soaking tub - I'm not sure exactly how much it holds but my current routine to fill it goes like this... I fill it to the point at which the water turns cool, turn it off and cover it (it's a Japanese cedar tub and holds it's heat amazingly well) I wait about 15 or 20 min and then fill it up the rest of the way. We like to end up with water that is about 99-100 degrees in the tub. Full it will hold this temperature easily for the time it takes the two of us to each have a nice soak. Covered up overnight it only drops to about 84F. (water is generally kept in a wooden tub as complete drying could crack the tub- we completely empty it to wipe it down several times a week, but on many nights I simply drain it 2/3rds and top it up with fresh hot water)

It would be nice to be able to fill the tub all in one go and to get rid of the bulky tank in the basement, but I'm wondering if a tankless heater would be more trouble and cost than it would be worth and will it even work well for this application? Will it make showering awful.. we don't use the too shower much, but still would want to have a comfortable spritz when needed.

Another thing we can consider - replacing our regular water heater with another tank style one and using a small point of use electric tankless as a booster- the wall behind the tub is open right now (and we can leave an access panel in it if need be)

 

[Jadnashua]

What is your wintertime cold water inlet temperature? If it is moderate, you might get enough hot water volume, but if not, it can get either cool, or very slow output of the tankless.

If the tub holds temperature well, you could probably get by with filling it slower in the winter (if you choose a valve that has a volume control), but your overall time to fill it might end up the same. To extend the volume of your tank type heater, install a tempering valve and raise the storage temperature, and you'll probably be able to fill the whole tub in one shot for much less than a tankless that not every plumber can fix or get the parts for if it fails at night or on the weekend...tanks are quick and easy to either replace or fix, should it come to that.

 

[Sponsor]

 

[Eden]

Looks like our water is hovering right around 42F right now and this is probably about as cold as it will get. Our water does come out the Cedar River watershed and even in summer is largely snow melt, and so I think doesn't warm up as much as it might otherwise.

 

[Jadnashua]

That might be warm enough, but I suggest you try to read this and see how the numbers work.

https://terrylove.com/forums/index.php?threads/tankless-wh-by-the-numbers.62457/

The cost to install one is not inconsequential, especially if you need a larger gas supply, then, there are other issues...none insurmountable. An informed decision will let you decide if it really is for you. FWIW, a modern electric WH is pretty efficient as they've mandated more insulation than the older ones, so standby losses are minimal, especially in conditioned spaces. A heat pump tank type can be more efficient, but they're not cheap either, and you'd still need the space.

 

[Cacher_Chick]

For overall cost over the life of a water heater, tank style heaters are a better value.

 

[Dana]

Unless you really need to recover a couple square feet of floor space, there's really no point in going tankless. Tub fills are usually SLOWER with a tankless than with a right-sized tank type water heater.

A timer on an electric hot water heater saves you nearly nothing. The standby losses of electric tanks are low, and the recovery times are slow. Only if the timer turned it of right after depleting it with a big draw like a tub fill would the savings be measurable, but even then they would be small.

A typical gas-fired 50 gallon tank recovers in about half the time of a typical electric hot water heater, but if you're going to spent the kind of money it takes for a big-burner tankless you'll be better off just buying a 75 gallon commercial hot water heater. But you may be able to just get more out of what you have.

Measure the diameter & depth of the cedar tub it's 5th grade math to convert that to gallons. The volume is roughly:

depth x (1/2 the diameter) x (1/2 the diameter) x 3.14

eg: say the tub is 30" in diameter and 32" deep. Half the diameter is 15" so the volume is 32" x 15" x 15" x 3.14= 22,608 cubic inches.

A gallon of water is about 231 cubic inches, so the tub holds 22,608/231= ~98 gallons.

With a storage temp of 140F and incoming cold water of 40F you would have no problem filling a tub that size in one go with a 75F hot water heater, since about 1/3 of the fill-volume would come from the cold side. Depending on your water pressure & plumbing diameters this could take about 10 minutes, maybe a bit less.

Raising 98 gallons (= 817 lbs) of water from 40F to 100F (a 60F difference) takes (60F x 817 lbs=) 49,000 BTUs.

With a big-burner condensing 199,000 BTU/hr-in 190,0000 BTU/hr out tankless that takes 49,000/190,000= 0.26 hours or (x 60=) ~16 minutes, and that is assuming you have sufficient water pressure to get the full flow through the heat exchanger on the tankless (which isn't always the case.)

Measure your actual tub volume- you might be able to get there with the existing 50 gallon electric tank by raising the storage temp and adding a tempering valve on the output to limit scalding risk.

 

[Master Plumber Mark]

Read all the complaints about tankless....if that does not convince you
to stay away from them then you are basically a glutton for punishment

 

[Eden]

Lol - I have been reading the complaints about tankless... that is what has given me some doubt that it's a good idea. In theory they seem like a great idea - not storing a great big tank of hot water and never running out, but it sounds like even after all these years there's still bugs in the system and they don't necessarily deliver on the theory...

We can get a rebate from the city if we buy a heat pump water heater, but they are also expensive in the first place and they have some drawbacks, like slow recovery, and the need for more space than a normal tank, that make them sound like a bad idea for the situation.

Given that electricity is quite inexpensive here, it may be best to stick with a plain old electric one or replacing the electric one with a traditional gas tank, but I'm not sure how much reconfiguration of the basement that would require. Not having a tank in our already crowded basement was one big impetus for changing to gas. I think we will perhaps look into putting a booster near the tap though.

 

[Dana]

Have you looked at just maxing out the storage temperature on the existing electric tank and tempering it's output down to 120F or cooler? A 50 gallon tank of 160F water mixes with 50 gallons of 40F water to make 100 gallons of 100F water. Most hot water heaters can tolerate storage temps up to 180F, but it might take swapping out the controls to be able to adjust it that high. Most can boost up well north of 150F- codes in many areas now require a newly installed tank to be set to no less than 140F, and must be tempered down to any taps to sinks, tubs & shower (but laundry is allowed to be untempered.)

 

[JRC3]

Given that electricity is quite inexpensive here, it may be best to stick with a plain old electric one or replacing the electric one with a traditional gas tank, but I'm not sure how much reconfiguration of the basement that would require.

So you have nat gas to the house?

 

[Jadnashua]

NG will almost always be faster recovery and lower cost to heat your water verses electric. The downside is the flue, the greater standby losses (you do have a convection pipe in the middle of the thing!), and the longevity. It will be a rare NG WH that lasts longer than an electric one. It can happen, but it's not that common. Also, unless you get a closed combustion burner, you will be sucking in unconditioned air into the structure that you will then have to condition to replace the considerable air volume that goes up the flue.

 

[Eden]

@Dana - We don't intend to do anything to our existing electric tank as it really does need replacing - it's been on it's last legs for probably the last 20 years... the plan always was to wait until it died and then go to a different system. It just lasted a lot longer than we ever expected and as long as it worked there wasn't much impetus to change it. Now we do have another reason - I'm not so worried about it taking time to fill the tub - We did not put a huge super high volume filler on it. It's never going to take 10 min to fill it up and that doesn't bother me, but it would be nice to be able to turn it on and have it be the temperature that I want it to be when I turn it off, rather than fill it up part way, shut it off, wait for the water heater to recover, fill it up the rest of the way. The tub is very large and does hold quite a bit of water - I've estimated probably about 95 gallons, though on most nights we start at about 1/4-1/3rd full already and that water tends to stay a pretty even 84F.

A tempering valve may work if we decide to go with a new tank system, but I'm thinking that a point of use booster might well be a better solution - we don't regularly run out of hot water elsewhere in the house and the tub is probably the furthest point from the tank that hot water runs to.

Indeed - we already use gas for cooking and heating. We even had a stub put in in anticipation of changing out the water heater when we replaced the furnace a few years ago, but I'm doubtful a tank will fit in that space. We'd probably have to run the gas to the spot where the electric heater is presently located. I don't think that would be a huge deal though, so it is certainly an option we can consider.

 

[Dana]

Even with a direct-vented condensing gas water heater it still needs the volume (or a very high storage temperature) if the goal is to fill the big cedar tub in one go. The cheapest thing to do would be to crank up the existing water heater to the max and temper the output. Any new installation would require a tempering or thermostatic mixing valve on the output to meet code anyway.

If it only takes 15 minutes of recovery time to be able to complete the fill you are probably pretty close to being able to get there simply by raising the storage temperature.

But measure the volume of the tub and report back- that thesis may be provable with arithmetic.

[your posting occured as I was typing]

To know the size of the replacement that works, you need to know the tub volume. Point of use boosters are expensive and unsatisfactory solutions to something that is solvable by a higher volume tank or a higher storage temperature.

Measure the temperature of the hot water from the nearest tap to the water heater, so we have an idea of what your current storage temp really is. (Is it set to the max?)

 

[Eden]

I'm not terribly worried about the upfront cost... While I certainly don't desire to throw away money, cheapest in the short term isn't necessarily my goal, but rather best solution in the long run. There is no maybe about replacing the water heater - I'm not kidding when I say it's long outlived it's life expectancy. It's at very least over double the age that an electric hot water heater usually runs and I doubt it was very new when we moved into this house in 1997 as it required some minor repairs at that time ( It needed a new thermostat, one of the two was not working, if I recall correctly) not to mention it's probably the bottom of the line cheap model, as nothing else the previous owners did was more than the minimum they had to in cost or effort.... As soon as I make a decision on a good plan of action we will replace it.

You might have missed it buried up in my last post - but I did estimate around 95 gallons are what is usually put in the tub, minus probably 15 gallons or so on many nights, as it's only completely emptied twice a week and there is no protocol for exactly how much I water I leave in... so if I were to get 100 gallons of 100F water out of a 50 gallon tank with a tempering valve installed that would likely work, though I'd have to keep the storage temperature quite high.

btw - we have currently bumped up the storage temperature as much as we have dared, but without any tempering and with the knowledge that this water heater will be replaced soon, we really aren't going any further at this point - my husband told me exactly where he put it a while ago, but I don't recall and can't measure it at this moment - 120F sticks in my head, but that could just be because I've seen that temperature written down so often recently or that could be where it was before. We don't have any children or elders to scald, but the water coming out of the tap right now is hot enough to be very uncomfortable to have your hand underneath even for a moment when full on.

 

[Dana]

For a 95 gallon tub fill a 75-80 gallon commercial electric tank at the code-minimum 140F storage temp with the code-required tempering would be appropriate. If upfront cost isn't an issue, a stainless commercial tank would last forever in a residential application (and comes with a lifetime warranty), and run about a grand for just the unit. The Westinghouse version is a bit less than 24" in diameter, about the same diameter as most 50 gallon tanks, and about six feet tall, which is taller than a 50 gallon tank. Doesn't eat up more floor area. You can dial back the storage temp to a bit less than 140F to save on standby loss, if it still fills the tub but the installer is usually required to set it up for140F, with tempering. Below 120F would put it into the legionella-risk zone.

Speaking of legionella risk, bathing temperatures are in the peak legionella growth temperature region, so leaving it filled or partially filled at those temperatures comes with some risk.

The big orange box store carries them, if you can't find it elsewhere. For some reason they have the 80 gallon 4500 watt version priced ~$160 more than the 5500 watt version.

 

[Master Plumber Mark]

I am installing a RHEEM 105 gallon MARATHON electric water heater next week....
Installed cost about $2400
It comes with a LIFETIME WARRANTY on the tank
The unit sits about 30 inches round and about 5 1/2 foot high
You ought to consider this over all the other options...

I am pretty sure it will fill up your whirlpool tub
and you will have hot water and bubbles shootin up your ass just fine...

depending on how you adjust the jets...

This one is a 75 gallon unit

 

[Eden]

Lol - my bath is a much more zen like experience, but I will look into that water heater. I get the feeling it's time to go and have a face to face chat with a supplier.

 

[Master Plumber Mark]

Thats your tub....Seriously???? Seriously???

What good is a huge tub like that if you cant have hot water
and bubbles shooting up your ass???


you can see that Marathon unit and get a price for it on line at
Home depot..

 

[WoodenTent]

I put in my tankless electric probably 5 years ago. Works perfect. I'm in Michigan, we have had some very cold winters. I've never had any issues what so ever. I have a small house, 1 tub-shower. It's a 29kw unit and cranks out all the hot water I ever need.

Cheap to run, silent, takes no more space than a pizza box stuck to a wall.

Bonus's include being able to set it to shower temp (110) and leave it there. No tank means no Legionnaires like you would have doing that with a tank. Hop in the shower and just turn on hot full blast. Never have to keep adjusting to get the temp right with tank setups.

Some day I will probably put a glass lined pre-tank in the house. This is just for more energy savings (use house heating (heat pump) to warm water up to 70F, instead of having to heat from 55F. Heat pump has a Coef of Performance thus more efficient than the straight electric of the tankless. But still no legionnaires issues.

If you don't have the power source for a tankless, than would be a reason not to go for one. But really it's more of a reason just to get your house upgraded to a 200-400A service if it doesn't have one all ready. Unless you have multiple people taking showers at the same time, I really don't see a problem with a tankless.

 

[Jadnashua]

29Kw is a bit over 98K BTU...IOW, not a lot when you're talking in-line, tankless, 'instant' heating. The thing would draw about 120A, and with the 80% rule, which I think would apply, would require a 150A circuit which puts it out of the realm of possible for many people without a major power upgrade. FWIW, most of the tankless, gas units top out at about 200K btu, which would require 300A to replicate in electric.

Most people don't shower with more than about 105-degree water, but some things do work better with hotter water, and if you need any volume, getting it with an electric tankless isn't likely to happen.