Water heaters rusted and leaking. Thinking about going tankless. Lowes has a 6gpm for around $500. Pros/cons? How many gpm do we really need? Are they a good idea?

I went back and forth on putting one in when we built. I go back and forth on if I made a mistake.

I have a couple I have installed in my home, but they are small units that supply one bathroom/shower. Works great.

For a whole house, electric seem to take a long time to get the hot water where you need/want it.

I think you've got to get a gas one, if you do it. I don't know about 6gpm, but it seems low. If I have to replace, I'll go with a Rinnai.

I think the typical shower head is only spraying 2-3/gpm so if you are producing 6/gpm it should be plenty sufficient.

What is the temperature rating? Mine was rated 110 degrees, but in the winter I could never get hot water to the back of the house. Plus my water was extremely hard and I had to put a filter on the water line before it entered the unit. I had a Rinnai propane tankless.

I have a noritz gas tankless and couldn't be happier with it

I have Rinnia tankless in my house and have been very happy so far.

Only if you have gas. Electric tankless are no good

We have a navien tankless gas and havnt had any problems...

Go with gas over electric. Get the next biggest size than you think you need. You never know when someone is gonna run washer and dishwasher while you are in the shower. Most will go up to 120 degrees. They usually have an over ride to get it to 140 degrees for commercial applications but 120 has always worked for me. Just put one in a new house and had some trouble with gas line sizing so make sure your line is big enough. Don’t forget to flush it yearly at least that is recommended. I have one that is 11 years old that still works and has never been flushed but it’s twin died at 10 years old.

We love our tankless, and never running out of hot water is a plus with 3 teenagers. Ours is propane.

I have 27kva electric EcoSmart. It takes 3 40 amp 220 breakers which was no problem for us as we have 400 amp service. Mine works great with my pex manifold and while some fixtures takes longer than I want to get hot we are only talking a minute or two. I attribute that more to the pansified Californicator compliant low flow bathroom fixtures. But we’ve had three showers going at same time and all were hot. If I had to do it any other way I would use an outside mount gas version.

Depends on how many showers you have. GPM is what is based on in keeping the temperature steady not the pressure you will get out of them. Also you have to look at temp rise in the winter from ground temp. It will reduce your gas bill since your not heating a tank of water. Navien can be bent with pvc pipe while others have to have special vent.
If it's for just two I would stay with the tank.

I went back with the tank. The tankless I was looking at required 120amps of juice which would have meant running new wire as well as adding a breaker in my breaker box, which I do not have.

There are specific considerations. Placement in the home, interior or exterior, venting of combustion gases, hard water. Is old one gas? Venting properly?

There are incredible benefits. Lower gas bill. Continuous water.

They come preset to 120 degrees. Some require a modification to get to 130. 120 isn't great. 130 is perfect for most of us.

If you currently have to wait for hot water in a distant location then it's not gonna change with a tankless.

If you have hard water you'll need to be sure to backflush and clean the system every 9 to 12 months. No longer than 12. Scale build up can damage the core. Proper cleaning is essential. You can do it yourself after a youtube video. Or just pay to have it done. Not expensive either way. Really you should be doing this for tanked systems as well. That's what the drain is for at the bottom. Nobody ever does it.

When my tank water heater dies, I'll replace with tankless. No question about it.

Same here. Love mine.

Building a house now, and it will have a tankless propane water heater. Not sure I will ever own another house without one.

I replaced both my tanks with a navient (gas) unit. Haven't regretted it! I went with my particular model because it could be vented with a PVC pipe out of the attic, and it has a built in recirc pump to keep 105 degree water at the other end of the house at all times.