New Build - Water Takes Four Minutes to Get Hot (At Some Faucets)

[AZTom1]

We live in Phoenix and moved into a new house in September. It has a Rinnai (RL94iN) tankless water heater. House is two story, approx 2400 sq ft.

The showers get hot within a minute or so. One of the sinks in the master also heats up in a minute or so. The other master sink, which is about 20 feet away and closer to the water heater, takes at least four minutes to get warm and longer to get hot. The kitchen sink and the powder room also take 4+ minutes. Upstairs bathroom sinks heat up in a minute or so.

I don't know how this stuff works, but I'm guessing the sinks that heat up faster are plumbed more directly than the ones that take forever. Is this normal? Why wouldn't all of the faucets get plumbed directly? Was it somehow easier to do it this way? Does the builder have any responsibility here?

Thanks!

 

[Terry]

How fast you get heated water to a faucet is not in any building codes. There are many ways of supplying water to faucets, and they're all correct if sized to code. Some ways make for a quicker supply and some that share water may take longer, but also may use less pipe and fittings.
And add to that having a tankless which is at times is thankless when it comes to wait times, but thankfully if you're the last one in line for a shower, it's still going to happen for you.

 

[Sponsor]

 

[AZTom1]

How fast you get heated water to a faucet is not in any building codes. There are many ways of supplying water to faucets, and they're all correct if sized to code. Some ways make for a quicker supply and some that share water may take longer, but also may use less pipe and fittings.
And add to that having a tankless which is at times is thankless when it comes to wait times, but thankfully if you're the last one in line for a shower, it's still going to happen for you.

Thanks for the reply! So it's not a code issue, but is it shoddy plumbing? Is this something that most plumbers would take into consideration when they're plumbing a new house? Four+ minutes is a really long time to wait for warm water.

 

[Bannerman]

You haven't mentioned if there is possibly a recirculation pump and a recirculation return line.

If hot water is circulated to a location closeby to your Master bedroom ensuite which then loops back to the water heater through a return line, that would then explain why those fixtures are receiving hot water more rapidly than other fixtures where there is no recirculation provision.

 

[AZTom1]

You haven't mentioned if there is possibly a recirculation pump and a recirculation return line.

If hot water is circulated to a location closeby to your Master bedroom ensuite which then loops back to the water heater through a return line, that would then explain why those fixtures are receiving hot water more rapidly than other fixtures where there is no recirculation provision.

Nope. No recirc pump.

 

[QueBall]

The gold standard would to be having all fixtures connected to a recirculation loop with a short distance from the loop to the fixture (like within 5ft). But if the house is already built, and you did not specify this feature you will have a hard time retrofitting a recirculation system into an existing house in most cases. (also something people are unlikely to pay for or even be offered as an option building a typical modest cost home)


From what I read this model of heater can take about 30 seconds to deliver hot water from cold start. So everything beyond that time will be a calculation of how much distance it has to push water through your pipe system to reach the fixture. It's a pretty large unit, sometimes the smaller sized tankless heaters actually perform much better for startup time as they have less internal volume and a big part of the startup time is doing purging of air.

What style of pipe is installed? Is it all home run to a manifold by the water heater or is it a large main line branching off to different rooms/fixtures as it goes.

It seems like most new construction is home run to a manifold. And usually with 1/2" plastic PEX pipe. So by your heater you have a single pipe for every fixture in the house coming into the manifold. To get hot water, the entire volume of that pipe must fill with hot water. So the time to get from the heater to the fixture will be dependent on the total length of the pipe for the given pipe size. 30 second start up plus the length of 1/2" pipe and the volume of water it carries should be the way to calculate the time to deliver hot water. But 2400sq ft, not a tiny home, but not exactly so big that you would expect such a massive difference between rooms.

Possibility is there is some issue with hot water crossing over into the cold water side through a fixture that is closer to the heater. If that happens your heater may be pushing "hot" water into your cold system doing extra work to deliver hot water to the desired fixture. Turn off the shut off valves on every other fixture in the entire house except the one you are trying to test and then see if hot water delivers quickly.
If you find hot water is delivered quickly with all your other fixtures shut off it leads you on a path to figuring out which fixture might be allowing hot and cold water mixing through it's body when shut off.

Also look at the pipes around your water heater, is there any cross connection to the cold water lines with a temperature mixing valve aka tempering valve or anti scald device to control the maximum hot water temp? If you have such a thing if it might also be a point of failure allowing hot water into the cold side.

 

[AZTom1]

The gold standard would to be having all fixtures connected to a recirculation loop with a short distance from the loop to the fixture (like within 5ft). But if the house is already built, and you did not specify this feature you will have a hard time retrofitting a recirculation system into an existing house in most cases. (also something people are unlikely to pay for or even be offered as an option building a typical modest cost home)


From what I read this model of heater can take about 30 seconds to deliver hot water from cold start. So everything beyond that time will be a calculation of how much distance it has to push water through your pipe system to reach the fixture. It's a pretty large unit, sometimes the smaller sized tankless heaters actually perform much better for startup time as they have less internal volume and a big part of the startup time is doing purging of air.

What style of pipe is installed? Is it all home run to a manifold by the water heater or is it a large main line branching off to different rooms/fixtures as it goes.

It seems like most new construction is home run to a manifold. And usually with 1/2" plastic PEX pipe. So by your heater you have a single pipe for every fixture in the house coming into the manifold. To get hot water, the entire volume of that pipe must fill with hot water. So the time to get from the heater to the fixture will be dependent on the total length of the pipe for the given pipe size. 30 second start up plus the length of 1/2" pipe and the volume of water it carries should be the way to calculate the time to deliver hot water. But 2400sq ft, not a tiny home, but not exactly so big that you would expect such a massive difference between rooms.

Possibility is there is some issue with hot water crossing over into the cold water side through a fixture that is closer to the heater. If that happens your heater may be pushing "hot" water into your cold system doing extra work to deliver hot water to the desired fixture. Turn off the shut off valves on every other fixture in the entire house except the one you are trying to test and then see if hot water delivers quickly.
If you find hot water is delivered quickly with all your other fixtures shut off it leads you on a path to figuring out which fixture might be allowing hot and cold water mixing through it's body when shut off.

Also look at the pipes around your water heater, is there any cross connection to the cold water lines with a temperature mixing valve aka tempering valve or anti scald device to control the maximum hot water temp? If you have such a thing if it might also be a point of failure allowing hot water into the cold side.

Thank you for the detailed reply. I will run the test you suggest.