Does a recirculating pump defeat the purpose of on-demand water heating?

[MossRoad]

Regarding small water heaters under kitchen sinks and dishwashers...

I don't have one under my sink. I have a regular one in the basement about 20' away. When I do dishes in the sink, I close the stopper, squirt in some detergent, turn on the hot water faucet, cold water runs for 30ish seconds, then starts getting hot. By the time the sink has enough water to start washing the dishes, it's too hot to stick my hands in it anyway (without rubber gloves). There's no waste of water at all.

As for the dishwasher, don't all of them have heating elements anyway?

Just curious as to why people need instant hot water in a kitchen.

 

[Cord]

. I think he also wants to do this when a lot of temperature rise is needed, such as when the incoming cold water is ... cold ... during the winter. I am on a well.

First of all,; my qualifications. I知 on a well and I have a tankless water heater with a circ pump. Mine is a simplex unit. The statement that grind water is colder in winter is untrue. It痴 actually a constant temperature all year. The ground is a large heat sink and seasonal changes don稚 impact the temperature. In Wisconsin we use 55 degrees as a design temperature for ground water. This would be the base point for the temperature rise. Now determine what you want for gpm and you can look at the heater charts to determine if two units are necessary. Personally, I壇 pick a single unit unless you can稚 get the desired temperature rise out of a single unit. My unit is 200k btu input so it痴 a larger one. I believe there are now larger units on the market. I致e never run out of water, but when running hot water through the pressure washer I e noticed it痴 delivering 120 degrees instead of the set 140.

My unit has a small 3 gallon tank inside of it which I highly recommend because it eliminates the cold water sandwich. You are correct in that not all units are rated for a circ pump. The units turn on based on a flow sensor and the pump will fool the unit into continuously running. A circ pump compatible unit will base the need to burn on temperature instead.

Do I like my circ pump? No, I LOVE it! This is the third home I致e had a pump on and it痴 the only way I値l go. You turn the water on and 1 second later it痴 hot. No more waiting 5 minutes and running multiple faucets to purge cold water. Energy efficiency aside, the convience is worth it. To help save some money, I put my pump on a timer. It痴 an electronic 7 day type and I programmed it so the pump does not run when we?*e not home.

If you do choose to go with twin pumps, then make sure they communicate with each other so the units will alternate. This will keep the wear even between them. Also, a water softener is mandatory as hard water will kill these heaters. Other things that your plumber will need to add are some balancing valves if you have multiple loops, some check valves and an expansion tank. You値l want the soft close check valves because I do hear my valve clicking when the washing machine fills. The expansion tank is a hard learned lesson because you will get weeping from the t&p valve if you don稚 allow for 5hermal expansion.

Yes, the loop and return lines must be insulated. There is a section in the IRC that requires it.

Would I do this again? In a heartbeat. One of the best home decisions I致e made.

 

[plowhog]

Would I do this again? In a heartbeat. One of the best home decisions I致e made.

Thank you for commenting. Much to learn here. Now I need to shop for a water softener as well!! Our water does have some hardness to it.

 

[swnoel]

Thank you for commenting. Much to learn here. Now I need to shop for a water softener as well!! Our water does have some hardness to it.

I've recently retired from the HVAC field and have vast experience with on demand water heaters... don't do it if you're on a well , have a lot of minerals in your water, or are doing this to save money. They need to be serviced yearly even if you're told different. Any minerals in the water WILL come out of suspension and build up on the heat exchanger plugging it in short order. Go with a direct vent gas water heater. I see this all the time with wall hung boilers installed on 180* base board. It might look and sound smart but you will never get the efficiencies they promise unless it condenses and at those temperatures it can't. I've see too many being destroyed within their useful life span of 10-12 years due to the extreme operating temperatures. They are not designed for those continuous high temperatures. They too need to be serviced yearly or early death will come. Good luck don't become another statistic to the hype.

 

[plowhog]

Swnoel: We are already framing and there is no space allocated for a tank type heater. So I guess we get tankless, good, bad, or ugly.

Cord: very wise insight. I learned today that the model the plumber is recommending has a small internal tank and is internally set for recirculation. Apparently they have an option so you can press a button(s) in the house to force recirculation for a short time, like pushing it when you have dinner and then the recirc line is full of hot water when you are ready to do dishes afterward. This way, you get the benefits of recirc (when you initiate it) without having the thing drain electricity and fuel doing a recirc either all night long, while on vacation, etc. It adds one more thing to do but pushing a button is not that big of a deal. I'm told the system will work without pushing the recirc button but it would behave as if there was no recirc-- meaning a lag before you get hot water flowing out of the tap.

 

[Cord]

The ability to manually trigger the recirc is nice. It's something that I wish for a few times a year. However, you are missing out on the greatest advantage of a recirc system: the availability of instant hot water. I'd highly recommend upgrading to take full advantage of your recirc loop. For me, the button solution is lame. Would you want to push a button every time you want the furnace heat to come on, or would you rather have it be automatic? Think about it for a moment. Well, the former is what your plumber just signed you up for.

Fyi - often the "button" solution is used for "faux" recirc systems. What he might be doing is using the cold water line as the return line for the hot water loop. This is could be why the system can't run continuously. If this is true, for the added cost of some 1/2" pex, I'd vote for adding a dedicated return loop.

Sorry for the graphics issues in my prior post. It's a glitch that is created when I post using an Apple product.

 

[jwstewar]

We installed our Noritz tankless water heater 10 years ago now. Biggest issue is the wait time at the sinks in our upstairs bathroom. Couldn't be any farther from the heater. Heater should have been placed on the other side of the basement. I did the calculations based on the propane we were using vs. what we were using in the old house that burnt down. Even though we were now cooking with gas vs. electric before, we were using about $150 less in propane per year vs. the old tank water heater. If I can keep from it, I will never go back to a tanked water heater.

 

[IchabodCrayne]

Long answer.. Yes.

 

[Oldoak]

I think he also wants to do this when a lot of temperature rise is needed, such as when the incoming cold water is ... cold ... during the winter. I am on a well.

I am also on well water. The temperature of the water being drawn from the well is the same year round, Summer or Winter, makes no difference.

 

[Pinzgauer]

Been using tankless Bosch for a long time. We have a long run, almost a hundred feet to our master bath.

The trick is to put a recirculation pump in the bathroom with the appropriate valves, and only have it run when the bathroom light is on. You put it on a switched outlet or motion sensor. some of them come with Z-Wave and you can have them automatically run for times that are peak bathroom times.

I'll never go back to a tank water heater.

The two tankless in series does make sense if you're on the upper end of the GPM that you can get in a single heater.

But my Bosch unit allows us to take two showers simultaneously, which is all we've ever needed.

the only times we noticed an issue is when something like a washer is filling up that is closer to the water heater with less back pressure than the shower and it can steal the pressure. But that's only usually for a minute or less.