I think it depends on the temp setting and output of your hot water heater and how quickly it recovers. Also, the supply valve you select and how it mixes water. Because you likely aren't filling the tub with pure hot water. The valve is going to mix in some cold for scald protection.

I just tested our tub valve last night. We get 115' when it is on full hot. If I dial it down just a hair, it drops to 100'. I really would like a happy medium :( but we spent a good amount of time tinkering with the scald setting and I'm just happy I can get a hot shower, and at least the kids have a setting that isn't too hot.

I like hot water. If you're at all uncertain, I'd go bigger.

If it doesn't have an internal water heater, you need to return it no matter how good of a "deal" it was. Who wants to wait 20 minutes to fill it, and let it cool down, no matter how large your water heater might be?

BTW, I just did a project where the owners went tankless for the express purpose of being able to use a similarly sized tub. They have never been able to use the tub the entire 15 years that they lived in the house because there wasn't enough hot water for it. And they had even upgraded to a 75 gallon the last time the tank died.

Deals are only deals if they don't end up costing you more in the long run than just buying the right product for the job. Even if it's more expensive initially than the "deal".

You aren't putting 75 gallons of pure hot water is what someone was trying to say (I think). You might mix 60 gal of 120 degree hot with 60 gal of cold. OR, if you make the hot water hotter (130) you would use less, assuming you started with a full hot tank. I have a garden/soaking tub. I don't know what it holds, probably less than yours, but I fill it all the way up. With my old 50 gal tank I could use it, but anybody after me had to wait for it to reheat (gas). When the dip tube started to go I couldn't fill it all the way and that's how I knew I needed a new hwh. In the winter it used more hot water because the cold water was colder.

When I got my new hvac there was a Clean Energy program with incentives. The incentives allowed me to justify getting a tankless. LOVE IT! I can fill my tub and moments later my son can jump in the shower and never run out of hot water. I got the tankless because I love to soak and read especially when I'm chilled. Headed up there now!

btw, it stays warm enough for about an hour (no jets) so I don't know if you need an internal heater unless the jets cool down the water. I do start with it pretty warm though.

75 gal should do it, but look into getting a small tankless for it. I think they make "on-demand" hwh that you can hook direct to one room if you want.

4gpm is with what incoming water temperature and what electrical amps required? Over half of your available amperage in your panel? Electric tankless is an expensive way to produce hot water compared to gas. Unless you are an electrician to run the new dedicated line needed and a LOT of empty panel capacity, you're out of luck in having this be anything close to economical.

If it costs you a 5K electrical panel upgrade, you'll care about how expensive it might be. Electric tankless requires a massive amount of amperage. Most normal home electrical panels can't handle that as a retrofit. Even if you have one of the new 400 amp panels, you will, still need to have an electrician run a LARGE dedicated line from that panel to the heater. Electric tankless only makes sense in new construction when planned for from the beginning. Even then, electric rates make the hot water produced by electric tankers cost between 40-100% more than gas produced hot water from an equivalent gas tankless.

As to whether any of those would be adequate, you start with your coldest incoming water temperature. Then look at how many gallons per minute your tub filler requires. Then you do math. Their online figure are quite laughably optimistic.

My whole house is being remodeled. I'm getting new electric everywhere and I'm down to the studs in the master bath which is getting a complete rebuild. Running a new line won't be a problem. However, my electric panel is 200 amp not 400 amp.

And I have no current tub filler, it will be new so I'll just have to select one that is compatible.

Even if the electric tankless cost 200% more than gas I don't think it would be noticeable on my electric bill. How much can it cost each time I fill the tub? If I'm like most people, once the novelty has worn off I probably won't use it much anyway.

Others have mentioned getting a small dedicated tankless/on demand hot water heater/point of use water heater. I thought this Eemax heater fit the bill. If not this, then what?

I do not want to convert to tankless for the house but I'd like to find a solution to make this tub work.

And yes, someone asked earlier if this tub has an inline heater and it does, so I don't have to worry about the water getting cold while it's filling up.

on the second page of the spec sheet it has a chart with one section labeled temperature raise. One module only does a 22 degree temp raise at 4 gpm. SO if your groundwater is 55 you will only be able to raise it to 77 at 4 gpm. I like my water at least 100 degrees, so if the water is 55 and you need a 45 degree raise, it will only do 2 gpm, that's with NO other water mixed in, so it will take a long long time to fill. You said its 110 gallons or so, at 4 gpm it will still take 25 minutes...so you need something that can put out enough hot water to fill it in about 10-15 minutes (so it doesn't get cold waiting to fill) .

I know I like it warmer than 100 (maybe 105?) because back when I was pregnant I used to use a pool thermometer because they suggest pregnant women not bathe in over 100 degree. I was OK with 100, but wished it could be warmer!

If you have gas, then price out a dedicated tankless for it. Its probably easier then running a special electric line assuming you have gas anyway.

As far as the 75 gal tank. If it heats water to 130 and you use all 75 gal, that means you are mixing that 75 gal with cold water...how cold does your water get (didn't notice your location)? Try mixing 7 cups of your hottest water with 5 cups of your COLD water and see how it comes out. (I think that is the same proportions as 70 gal hot and 50 gal cold=120gal.

OK, this is very helpful information for me. I'm not knowledgeable about the ins and outs of hot water heating. Obviously! lol

If I got this little electric water heater, I imagine it would be between my existing water heater and my tub. So the water coming in would already be heated, it wouldn't be heating cold groundwater. Right?

If I get a dedicated tankless for the tub won't it be expensive to run dedicated pipes to the tub? To me this sounds like a complicated plumbing project but maybe not.

I suppose if you are heating your hot water it would be good, but I assumed you were heating the cold water. Why bother heating the hot water, wouldn't you possibly get it toooo hot?

I imagine (could be wrong) that you would have pipes going to the basement (?) anyway right? The heater would be in the basement and the plumber wold figure out how to arrange the piping. I think you would branch off the main water line and one water line goes to the hot water heater as usual and off to the rest of the house as usual, another line goes to all the cold faucets as usual and a third line goes to the tankless and direct from that tankless to your tub. You would just not have your tub connected to the original hwh. I think I have it right, but I'm just a "mom" so I don't know for sure. You need to have your plumber (assuming you have one for this remodel) look at it. Make sure he has done tankless before!)

Also, I think most water lines now are done with flexible tubing (pex) not ahrd copper lines so I think it is not hard to run them.

Why not just buy a much smaller volume soaker tub? You'll actually use it, and you won't need to spend 3K getting more hot water for it.

Because I want a nice, big, beautiful, two-person whirlpool Jacuzzi with neck massagers, led lights, air bubbles, jets, lcd controller, heater, etc. Also, as I said, I'm getting an insane deal on this. Paying less than I would for a much more basic tub. I could never justify a $12K splurge on this tub if I wasn't getting the deal of a lifetime.

See the attachment and you might understand why I want it. This isn't even the top of the line model which is what I'm getting.

That 40K almost classic Ferrari sure is great! Until you find out that the 50K mile service--- and subsequent services--- can only be performed by the dealer with the specialty Facom tools, to a tune of $34,000.

N one ever sells something that they found useful and want. They always have a reason for getting rid of it. Figure out that reason before acquisition of the product puts you in the same boat.

I believe she got it from a store since she said something about a salesperson.

Uscpsycho - I know this is an old thread but I'm interested in learning what you finally ended up doing. We may have a similar situation. What did you do, how well does it work, anything you would do differently? TIA!