We installed a Rinnai tankless hwh two months ago. Now it takes about 30 seconds to get warm water and 40 to get hot. With our old electric hot water tank it used to take under 15 seconds to get warm and 20 to get hot. (I tested this first thing in the morning when the hot water hasn't been used for many hours.)

I think the main problem is that the tankless hwh is located much further away from all the hot water faucets - but it doesn't matter which faucet I test this on. The "pipes" from the tankless are PEX - about 25' until they tie into the copper - could this make any difference?

Does anyone have any tips on reducing the lag time from turning on a hot water faucet to actually getting hot water? I guess we could move the tankless closer to the faucets - is there any rule of thumb for lag time to length of pipe run???