My father-in-law has a five-bedroomed house with three bathrooms, two of which are in use. The household is gravity-fed with a cold water tank on the roof, and a gas-fired tankless water heater on the uppermost of three floors.
It is only possible for one shower or tap (faucet) to be used at a time without reducing pressure. If the kitchen sink is used (hot) then the shower can reduce to a trickle.
I have read that a second heater, connected in parallel, would permit a higher outlet pressure at the temperature of a single heater, but my father-in-law is suggesting the installation of a pump at some point in the system to permit more than one hot water fixture to be used at the same time.
Is this possible, and can anyone with experience offer some advice on the general setup?
N.B. the house is in Mexico, so specific product recommendations may or may not be helpful.