How many people are in the house? The 'small' Tempra will only serve hot water to 1 faucet at a time. Per the website. It takes (2) 40a. Circuits. And (2) 2 pole breakers. Electrical load wise, it may not require a panel upgrade. Consult a licensed Electrician. The larger Tempra Plus unit, as shown, when you turn on multiple faucets, it puts heater to each, just a smaller flow. And requires a panel change out to a 225a. Panel, (3) 40a. Circuits an (3) 2 pole 40a. Breakers. I spent approximately $900 on the heater and approximately $700 on materials, including breakers, wire, pex pipe and fittings, and brass fittings for the recommended twice a year back flush. I consulted a licensed Electrician, myself, and with just 2 of us at home, I elected not to upgrade the panel. THAT (if I paid someone), would have been approx. $3,500 by itself. Many plumbers do not install electrical units do to these unknowns and plumbers are afraid of electricity. DO consult your local building codes, DO seek advice from a local professional. I am just answering a question as it happened at my house.