I have a whole house tankless water heater installed, and so far it's nice except one problem. I also have a nonelectric hot and cold toilet mounted bidet installed. Since a high pressure jet would not make the bidet suitable for it's task, it's max output is less than 0.4 GPM.
The tankless heater has an activation flow rate of 0.4 GPM and the bidet fails to pull enough water to start it heating.
The current solution is to run either the sink or tub hot water to avoid a very cold jet of water in an uncomfortable place.
Is there a common solution to this issue?
I'm considering getting a 2 gallon mini tanked water heater for the bidet. I think that should be plenty, but I'm worried that a small tank heater would have a lot of surface area and lose heat fast. It would have the advantage of being local and instant, as long as it was installed near the toilet.
Alternatively I could get point of use tankless water heaters. I have one installed in the kitchen in series with the whole house unit to boost the temperature for the faucet and dishwasher. That works good, but I'm having trouble finding one with a low enough activation flow rate for a bidet.
A third option is to use an electric bidet. This has some nice bonuses, but I don't really want to do that. They're expensive, and since they're all in one units, then each additional function is an additional point of failure. I'd rather keep the bidet and water heating separate. Further I already have the bidet, and toilet seat, and don't want to replace them if it's reasonable and possible.
So what I'm looking for is more information.
How is a low flow appliance normally handled with a tankless heater? Is the minitank a good solution energy wise? Should I look harder for low flow point of use tankless heaters? Is there something I'm not aware to solve this? Thank you.
Best Answer
Thanks to MonkeyZeus suggestion. Here's the answer I'm trying. If you look around you can find a 12VDC Circulation pumps that do 2 GPM for under $50.
Simply install an outlet in a location safe from water near the appliance or fixture that has some means to control it whether a switch or motion sensor.
Install the pump between hot and cold lines. Plug the Pump's AC adaptor into the outlet mention above. And life is good. A bonus is no water is wasted getting the water heater up to temperature.
Edit: I'll mark this as correct once I have mine installed and made sure it's working good.
Update: installed and working good!
I used these parts: 1/2" Back-Flow Preventer: https://www.amazon.com/gp/product/B000EDUTN6 Hot Water Heater Circulation Pump with DC Power Supply Adapter 2.1GPM: https://www.amazon.com/gp/product/B01G305PK0
The incoming hot water line is 1/2" pex, going to the bidet, and the out going cold line is 3/4" pex, because the shower line was easier to connect to for that. Per the comments, I added a backflow preventing valve. The pump didn't come with one.
You can hear the pump running, and once it kicks on there's hot water in the line in less than 20 seconds. Works so good I'm going to install one on the kitchen faucet.
The pump it's self is submersable, 12VDC, and low amperage. Parts including the pex connectors, crimps, and such was less than $50 and took less than an hour to do. Most of it was figuring out the in and out on the pump.
The install is less than 10 feet from the water heater, so this may not work for longer runs, or narrower pipes, or some other variables. I mention this because the pump isn't rated for longer runs. It works good for my loo, that's all I know.
Haven't yet put the motion sensor switch and outlet in yet, but I'm confident about those.