Just bought a twenty year old house in Loveland, CO. Has a two year old gas 50 gal. water heater in downstairs closet. Upstairs in master bath is a huge jacuzzi tub. Largest I've ever seen. Problem is the there isn't enough hot water in the heater to get the jacuzzi near full. Can another hot water heater be piggybacked onto the present unit? There is enough room in the closet for a lowboy unit. Before you ask, the jacuzzi is in a punchout surrounded by glass so there's nowhere to put a water heater dedicated to the jacuzzi. The only other option would be to put a water heater in the clothes closet (it's big enough) but the water lines would have to go up and into the attic space to get to the jacuzzi. I think there may be code issues in doing that. Not sure that would be wise given how cold it gets here sometimes. Hints or suggestions would be greatly appreciated.

Sure many of times there are piggy back heaters that are used. One would be a pre heat to back up the next when you need more demand. You can also turn off the back up when its not needed
You would set the first hot water heater about 100 degrees or so and that dumps into the main heater and then to the house demand.
On some jobs I have used a auxiliary hot water heater to pre heat a domestic boiler coil to keep up with demand for when the home owners have big stay overs
You should do some math here and figure some out how many gallons you need in one demand call on the heater to get the gallons correct on the demand cycle


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Better solution to your problem is to install In-Line-Heater on your jacuzzi tub plumbing. No matter how many heaters you will install - once you fill up the tub, water will cool down rapidly. You will keep draining - and refilling - the tub. Heater will keep water on same temperature as long as the tub is running.

Insta heaters are pricey I've had no problems piggybacking many a small Trailer sized water heater, (if space is tight) or a 30 gallon Lo-Boy into a master bath. Tee off from the hot feed to of the main heater to the cold water inlet of the "kicker" heater and the hot water outlet to the tub hot water supply. If jumping the hot water up into a cold attic gives you concerns then insulate the pipe with Armoflex,(see image). Good luck and thank you for rating my answer. Tom