We’ve been exploring a thankless solution, but the company that quited us said it isn’t a good idea in our area because the ground freezes in the winter. We don’t live in a super cold area, but it does snow a few times a year and it can get into the single digits of degrees Fahrenheit.
In that case, I would assume they’re talking about how cold the incoming water would be.
I used a tankless in a zone five area where our incoming water in the winter was often below 60 degrees. You’ll have to compare the charts of input temp and output GPH to determine how it would work for your specific use case.
I used an indoor mounted one, but there are tankless models intended for places like CA and AZ where they can be mounted outside.
We liked the endless hot water - we only had one bath and three people, so we offer were bumping against the 60 gallons of our old tank model.
Our biggest issue is that we have a huge hot water heater that takes up a whole closet. We like to down size. An indoor one would be fine. What are zones?
The tankless heater should have a map in the specs divided into zones by average water temperature. There’ll then be a table that references the zones and what size you need for what you expect to heat at the same time.
You should spend some time reading the literature of tankless heaters - the child post below explains it. Tankess heaters can only raise temp at certain flows. So, if your incoming water is ~55 degrees, it might be able to heat to 110 degrees and flow 6.6 GPH - basically one shower. In that scenario if someone turned on the hot water for… say… dishes, the tankless can’t keep up with demand and the overall output will be colder. Probably not cold but it might not be what you wanted.
The more expensive you go, the more the tankeless can do concurrently, but the more sacrifices you’ll make: they’ll be physically larger, they might require a bigger gas line, etc.
That’s why we installed a tankless unit, it freed up an entire utility closet because we were able to tuck it in to a pretty small space while still respecting the required clearances. The only downside we’ve had was initial cost, and the yearly flushing process, which really isn’t bad if you install the correct valves from the beginning. Takes about 30 min. a year, which is worth it for endless hot water. Our gas bill has also been lower too.
One thing to consider also is that tankless water heaters need a considerable amount of space around it because it needs adequate air flow. So if your water heater is in a closet, it might not work anyway.
I’m assuming they’re referring to hardiness zones