You are talking about insta-hot water heaters that give you instant hot water at one faucet. A tankless water heater can serve several faucets as well as showers or whatever else you may need hot water for. Insta-hots don't have the capacity for showers. The tankless system takes the place of a conventional water heater. It is mounted in a closet or garage not under your sink like the insta-hots. Tankless water heaters use the existing piping in your house. They are designed to take advantage of the energy saved by not continuously heating a large volume of water like a conventional water heater. The only down side is the high initial cost of the tankless heaters.

 

Tankless water heaters require a larger (5") exhaust ducting all the way through the roof, most conventional water heaters use smaller ducting, so you have to enlarge the passage-ways through the walls and through the roof.

 

are you sure? Most of the ones that I've read about mentions nothing about an exhaust cuz it is electric.

 

I've only seen gas tankless units at H.D.

Natural Gas is slightly cheaper than electricity

 

You can direct vent tankless water heaters straight through the wall to the outside. Some tankless heaters use the standard 4" flue, so no changes would be required. It would not be worth it to buy an electric tankless heater b/c you don't benefit from the energy savings. The only reason to buy an electric unit would be either there aren't any gas lines close by or you have space limitations.

 

we have a gas tankless water heater set at 140 (Rinnai continuum model v2532w) mounted on the side of our house so venting isn't really an issue. It takes a tad to heat up the shower at the other end of my house (sprawling 1 story so about 60ft maybe more away). But, I love the thing. It's gas and our bills have gone down significantly from our old gas tank water heater. I've taken a shower with the dishwasher and other shower running with no problems. I drained and filled our indoor japanese style hot tub today which is quite large (3 person) thinking I couldn't use it tonight because the added water would run cold and the little motor for the tub wouldn't be able to heat it in time, forgetting that we got this heater. When I got back, the water was too hot to use and the water coming out of the facet was still piping hot. Only problem, heater was 3,000.

 

The tankless ones don't waste energy keeping 50+ gallons of water hot all day and night while you aren't running water.

Plus it doesn't use gas until someone cracks open a faucet.

 

I wanted to get one and was willing to pay extra, but it is really tough to find installers for them and the great City of San Jose had not yet approved them for residential use (about a year ago) and I didn't want to have to deal with any up-to-code issues if we were to sell the house. They are great and you should get one if you can, but nothing is without issues.

Jimbo