There will be no problem reducing on the in and out, what you really have to consider is the size of the gas line to feed a tankless heater. All that I have seen require a 3/4" NG line, which will probably lead to issues with having enough gas/pressure for both your furnace and the tankless heater.

Mark

 

I agree with Jack.
Most residential water heaters are rated at 40,000 to 50,000 BTU's.
You tank less is going to be over 200,000 btu's. Not many home have that kind of excess capacity in the gas system.

 

Thanks for the fast post Mark. I asked the salesman about the gas line too. I have 1/2 inch NG pipe and he said the models they sell 'Eccotemp' are 1/2 inch. I was assuming I was good there but please let me know if I am wrong.

Thanks again.

jake

 

The model the guy was talking about is 'Eccotemp FVI-12-NG'. I have a 2 bed, 1 .5 bath home and he said this should be good. I normally don't do laundry or run the dishwasher together or when I'm taking a shower so that's what he recommended. It looks like its 74000 BTU so I'm hoping my current NG line will work. What do you guys think? It looks like it will be an easy install for me. I only need to modify a few things with the plumbing so my thought is if it doesn't work for me its only an hour or two.

 

By the way hello Jake and welcome the best DIY'r site on the web.

Tankless heaters are rated for gpm at a given temperature rise, that being said I looked up a small eccotemp (3.5 gpm) and it was 75,000 btu's/hr.

The problem with that small a capacity is yes it will run from a 1/2" gas line as long as the line isn't too long, but if someone else in the home turns on the HW tap, the shower goes cold.

At a minimum a house with (4) peeps in it needs at least 7.5 gallons which would be more like 200,000 btu's/hr.

Mark