Water heater for bathtub

[FLhome0wner]

I am remodeling my whole house at the moment and adding a new 95 gallon bathtub but only have a 40 gallon electric water heater. It is a 3 bathroom house with 2 showers and 2 bathtubs. I do not have gas at the house. I've never lived in the house, so I don't know if I currently have enough hot water. This is in Central Florida with an inlet water temperature of around 72.

Should I upgrade my tank water heater to a 100 gallon one for just this bathtub? It will likely be used once or twice a month.

Should I add a tankless electric heater just for that tub with a flow restrictor on that tub to control flow rates? I was looking at an ecosmart 36kW water heater or maybe something smaller.

 

[Jadnashua]

Running some rough numbers, no, it won't work. That electric heater would need to be much larger, and you would almost certainly won't have enough power available.

95 g = about 800# of water. If your valve can produce about 6gpm, 95/6=16 minutes. Let's call it 15, so 800# * 4 (to get a one hour, which is how those things are rated), would require 3200# * 35-degrees = 112K BTU. 35Kw = about 12K BTU, or about 1/10th the amount you would need.

 

[Sponsor]

 

[Dana]

It doesn't take 100 gallons- an 75-80 gallon tank will do it.

With 72F on the cold side and 140F storage temp in the tank it takes 55 gallons of 140F water + 40 gallons of 72F water to deliver 95 gallons of 111F water, which is about as hot as you'd ever want the tub.

An electric tankless is a bad idea even if only serving up a shower, but a downright miserable way to fill a large tub. With an electric tank sized for the tub the fill rate is only limited by your water pressure and plumbing. With a tankless it's limited by the power capacity, which is enough to cover a shower at your incoming water temps (though it's really abusive to the power grid), but an exercise in tedium for filling tubs of any size, let alone a big 'un.

 

[FLhome0wner]

Thanks for everyone's responses. I think I'm going to go with a heat pump water heater from Rheem.

 

[Dana]

Thanks for everyone's responses. I think I'm going to go with a heat pump water heater from Rheem.

To have any margin on tub fills with a heat pump water heater go with the 80 gallon. The 65 gallon Rheem might just barely cut it on the tub fill in summer, but probably not in the the winter. Recovery times on heat pump water heaters are pretty slow, so the extra volume after a tub fill is going to matter.