30Amp available to "boost" hot water going to tub

[DIYinATX]

So, I've got a 40 gallon traditional hot water heater supplying my house.
Works terrific for everything except my massive jacuzzi bathtub.
Water gets cold before I can finish filling the tub.

I was thinking of getting a tankless water heater "booster" to help out but I only have 10awg/30A available at the tub.

Rewiring everything or upgrading to a larger tank isn't possible right now.
I don't have gas available either.

Same issue at the 40 gallon tank. It's only got a 10awg/30A, so I can't replace the 40 gallon tank with a whole-house tankless.

Are there any options for me?
I'm getting conflicting info about whether a 1.5GPM single-point-of-use tankless would help or not as a "booster".

Thanks!

This is the booster I was looking at:

Robot or human?

 

[Breplum]

A tempering valve is one thing to try.
Webstone makes good ones.
Allows you to turn up the WH to very hot, but the water coming out can be adjusted to a safe temp to prevent scalds.
I doubt it will solve your problem.
You really need a tankless WH to provide unlimited hot water.

 

[Sponsor]

 

[wwhitney]

Are there any options for me?

Say your incoming cold water is 50F, and you want 80 gallons of 110F water. That's 4800 gal-F of energy you need add.

If your tank has 40 gallons of 140F water in it, that's 3600 gal-F of energy stored. May not be possible to get all of that energy out usefully, due to dilution.

If you could install another 40 gallon tank near your tub, that would work.

A 7.2 kW heater can provide 50 gal-F/min of energy. So if you have a 1200 gal-F deficit (best case) it would take 24 minutes to provide it.

Adjust the above assumptions as required for your situation. But doesn't seem very practical on the face of it.

Cheers, Wayne

 

[DIYinATX]

Thanks, folks!

The tub fills is rated at 3.1GPM flow rate through 1/2" PEX.
It takes about 30 minutes to fill using only the incoming hot water line.
In the summer it works out okay. This weekend was very cold outside and I ended up with a lukewarm jacuzzi tub.

The annual average water temp in Central, Texas is in the mid 60 degrees.
Colder in winter, warmer in summer. Our winters are mild though.

Would a Tempering Valve help by "heating up the water in the tank quicker" because I can adjust the temp much higher?
Thus, allowing me to get a little more hot water out of it in the same amount of time?

In about two years, I'll be able to upgrade my panel and run some 6awg up to the tub.
Until then, I need to "squeak by" somehow.

 

[Fitter30]

Here's a water calculator hot to cold just change settings to gpm and f°

 

[wwhitney]

Here's a water calculator hot to cold just change settings to gpm and f°

I think you forgot the link.

You can also use 1 kW = 6.8 gal * F / min. I.e. 1 kW can raise a flow of 6.8 gpm of water by 1 degree F ; or a flow of 1 gpm by 6.8 degree F, etc.

Cheers, Wayne

 

[Bannerman]

Would a Tempering Valve help by "heating up the water in the tank quicker" because I can adjust the temp much higher?

A tempering valve will not cause the water in the tank to heat quicker, but will increase the apparent capacity of hot water available from your existing 40-gallon tank.

When the water temperature exiting the WH exceeds the desired water temperature, a tempering valve will mix cold water with the hot water so as to provide the desired temperature (ex: 125℉) to the faucets. If the hot water temperature is 160℉ or hotter within the tank, then a substantial quantity of cold water will be needed to reduce the water temperature back down to 125℉ at the faucet, thereby increasing the quantity of hot water that is available from your existing 40-gallon WH.

 

[Fitter30]

This might help" oldtimers"

Water Mixing Calculator | Spirax Sarco

This calculator will help to consider the mixed temperature of two water streams, its flowrate, percentage flow and actual flow of each stream.

www.spiraxsarco.com

 

[DIYinATX]

Thanks! I'll go ahead and research Tempering Valve options for purchase.
They're more expensive than I thought they might be ($100-$200+)!

 

[DIYinATX]

Was the tankless "booster" a dumb idea?

 

[Bannerman]

A 2nd 40-gallon tank type WH, plumbed in parallel with the 1st WH, would double the quantity of hot water available.

 

[DIYinATX]

I wish! A tank is out of the question now and probably in the future as well.

I might be able to expand from my current 38 gallon to a 50 gallon next year.
Am dealing with a 40" height limit (and 30" width).
Might be able to stretch that out to 52" height for a 50 gallon shorty, but won't know for sure until next year.