Visiting my daughter and son-in-law in Austin---their upstairs shower needs several long minutes for the hot water to come up. What is better, faster, cheaper? I was going to spring for installation of one of those $300 On Demand thingies at Home Depot, but my own plumber says it is only good for six (6) gallons.I thought that the devices might have to be installed to each site,kitchen and bathrooms. I want them for my home too. Had no idea that the thing is limited to six gallons. It could work if the first 6 gallons were heated onsite with this device---until the regular long run from the hot water heater finally made its arrival. Any solutions?