I did an 11th month inspection this morning. The family has a tankless water heater. A complaint they have is if they are showering and any other water is running in the home the shower goes cold. My client mostly described it as when shower and laundry are going at the same time. No loss of water pressure, just heat. I know tankless heater require high BTU’s.
I have some pictures but can’t load them now, will upload pictures if necessary. Thanks for your thoughts 
You don’t need any pictures to write up the fact that the client is using more hot water than the appliance is capable of producing (on-demand).
Look up the specs for the brand/model installed in the home, and you’ll learn the flow rate (gallons per minute at x degree rise), temperatures it’s capable of producing, gas inlet specifications, etc.
Dom.
That is a very good link Roy. Thank you.
On 90% of the tankless I run into, the gas meter is not capable of handling all the gas utilities in the home. Most tankless start at 198k btu. Add in another 50-75k for a range, another 35k for a fireplace and top that off with a 50-100k furnace and you are well over the standard gas meter of 305k. And if they have a bbq stub out, that counts as well.
My last job working for someone else was selling/specific application of plumbing and heating equipment and material.
One of most misapplied products are the tankless water heater.
Like Dom indicated the BTU ratings are near 199,000 BTU’s. Gas piping requirements and supply are critical.
If you look at the sizing tables for the Rinnai gas fired models, a 65 degree rise will only get you 4.3 GPM.
Perfect for a middle aged couple with no children at home, but not for a young family…
So, as an inspector advising a client on an 11th month inspection. If the unit is not providing suitable usage for the families needs is there any deficiency they could reasonably expect the builder to address? Or would y’all say this is just the way it is?
If I see any installation deficiency (e.g., a gas supply less than 3/4 inch) I will report it as a defect. If they feel that they are getting insufficient hot water supply, and you can’t visually determine a deficiency, they should report that to the builder under warranty coverage themselves. They should look to you to help them identify warranty issues that they don’t already know about. They are not dependent on you to report their own observations that they can report themselves, particularly those that you can’t objectively evaluate - unless you are equipped and prepared to measure temperature rise at a known flow rate to compare against manufacturer specifications.
If the meter is not large enough to handle ALL the supplied gas appliances, it should be changed.
If the main gas line feeding the meter is not large enough, it should be changed.
If the gas lines within the home are not large enough, they should be changed.
Those are builder issues.
Good info Thanks … Roy
I am thankful for the great learning opportunities on here. Thanks for the good info gentlemen.
There was some good information on the link A lot of it I was aware of but never hurts to be reminded. Watched the youtube video link at the bottom. Amusing