Long version (skip below for tl;dr)
I recently purchased a new house. (first owner) 3 floors, unfinished basement where the hot water heater is located. Approx 3300 sq ft.
When looking through the house, I was shown a tankless water heater. Red flag immediately goes up. Whatever. I later discovered it's a GAS tankless water heater. I didn't even know that was a thing, but seems like it's the worst of both worlds. My worst fears were confirmed: It takes OVER 2 minutes to get hot water anywhere in the house.
The tank is on max heat (120°F) We have PEX throughout the house, and it doesn't seem like there are any inefficient lines, so my assumption is it must be the water heater itself. Of course a tankless heater takes longer to get the hot water than a standard one, but 2 minutes seems quite excessive.
The "unlimited" hot water is nice once it gets hot, but there must be a better solution.
TL;DR
Gas powered tankless water heater takes too long to heat up, looking for a solution that still allows us to have the benefits of not running out of hot water but also provides hot water in a reasonably short amount of time.
My idea:
Get a small tank (I'm thinking 4 gal is big enough, but the smallest that is commonly available should be sufficient) gas powered water heater that I can use to either A) feed into the tankless water heater or B) feed FROM the tankless water heater, but either way basically install the 2 inline so that we have both ready-to-use hot water and also limitless hot water.
My question:
Would it cause any problems with either machine to have hot water fed INTO the machine rather than cold water? Is there a better way to handle this?
Best Answer
The problem is probably not the tankless these heat the water extremely fast, the real problem is probably the size and length of pipe to the point of use. A tanked water heater will probably take a similar amount of time to get the water hot to 120 at the point of use, what I have done is installed a small tanked unit after the on-demand with 2 check valves and used a recirculation pump at the furthest location cycling the water through the loop with a timer. One check valve prevents reverse flow through the loop and 1 to protect the tankless. We did insulate the pipes were accessible and this worked once we got the cycle on off time adjusted, I added the check valve between the 2 to protect the tankless with the tankless kind of isolated from the small tanked heater there were no false turn on's on the tankless (recommended by the mfg). This method will increase your electric usage but the small water heater 7 gallons was enough to keep the hot supply on a ~3500 SF ranch home with 3/4" water lines. Recirculation systems are not bad when you have large lines that are long but because all the lines are kept warm it cost more but the good news is it can be done. On smaller homes I have installed 2 point of use electric units 30 amp. But with larger homes the combination of a large tankless and a small tanked system with a recirculation system is much much cheaper.