In-line water heater suggestions?

January 23, 2011 2:11 PM

What kind of water heater can I put under our bathroom sink to heat the water until the house water heater takes over?

The bathroom and current water heater are at opposite ends of the house so we get about a minute of freezing water before the hot arrives. I want something that will heat the water nearly instantly, but will shut off when the incoming water is hot enough to use directly.

What should I be looking for? Do you have personal experience with something along these lines?

posted by odinsdream to home & garden (12 answers total)

To be honest with you, I think any solution to your problem will be a bit Heath-Robinson-esque. The simplest solution is to just run the tap for a bit before using it.
posted by dougrayrankin at 2:24 PM on January 23, 2011 [1 favorite]

I think what you want is a point of use heater
posted by InkaLomax at 2:30 PM on January 23, 2011

Under-sink water heaters are readily available. Once you've invested in heating the bit of water you want at first, there's no reason to switch over the the main water heater, you've already done the hard part and would just be making the system more complicated and prone to failure. A google or amazon search for "under sink water heater" yields the exact products that would work.
posted by desl at 2:32 PM on January 23, 2011

Seems I was wrong. Disregard my comments.
posted by dougrayrankin at 2:33 PM on January 23, 2011

There is a point of use tankless water heater that answers your need. I found this product in the December/January issue of familyhandyman.com (p.60). The for more information links are: boschhotwater.com. hotwater.com/products/residential/rg-ondemand.html.
rheem.com/products/tankless_water_heaters/tankless_electric. stiebel-eltron-usa.com/mini.html.

This is my next project. I did have a plumber over to try and solve the issue before I saw this product and he essentially said the cost would be prohibitive (running another set of pipes, etc.).

Good Luck
posted by KneeDeep at 2:37 PM on January 23, 2011

We had this same problem. and installed a Metlund pump under the sink. Before taking a bath,. or using the faucets, we press a button and the pump installed under our bathroom sink circulates the water until it detects a rise in temperature, and then. the pump shuts off. It's as if you ran the tap before using it, but you're not wasting the water since it's being recirculated. We've had ours for over 5 years now, and it's worked out well.
posted by jaimev at 2:40 PM on January 23, 2011 [4 favorites]

I'll echo jaimev's suggestion. Though you might consider setting up an IR motion detector, so the pump kicks on when you enter the bathroom.
posted by herrtodd at 4:03 PM on January 23, 2011

Probably more expensive than what you're looking for, but the normal industry answer to this is to put in a hot water recirculation line. Install a line from the furthest fixture in your house back to the water heater, with a circulation pump to keep warm water flowing. With the pipes properly insulated this doesn't place a significant heat load on the water heater. This is more labor intensive, complex, and expensive than the medlund system, but it has the advantages of always providing hot water to your faucet the moment you want it.
posted by Mr.Encyclopedia at 6:12 PM on January 23, 2011

I should add that our house already has a tankless water heater, which works great once the water reaches the destinations.
posted by odinsdream at 8:41 PM on January 23, 2011

I think a secondary tankless hot water heater is your best option, given your circumstances. There are 220-240V electric models, common in some parts of the world although I'm not sure about the US. They are pretty compact and you might be able to find one that fits under a bathroom sink. The (likely) higher heating cost* from electric shouldn't be too much of an issue since the system will only be on for a couple minutes until the hot water from the primary water heater reaches it. Plus the electric water heater will be cheaper than a gas one to purchase and install and you don't have to worry about gas supply or venting.

The other option is a Metlund-type system. They have a page covering tankless water heaters. Primary downside is it's still not instantaneous, since you have to turn it on and wait a little bit, although maybe something like herrtodd's motion sensor might mitigate that.

The standard recirculation pump type systems for instantaneous hot water don't generally seem to be compatible with tankless, although maybe there are options out there.

*As a ballpark example, a 2 kW system running a total of 15 minutes per day at 15 cents per kWh would cost $2.25/month (2kW * 0.25h * $0.15/kWh * 30days).
posted by 6550 at 1:58 AM on January 24, 2011

What I'm not seeing is whether any of these in-line under-sink models monitor the incoming temperature. They all seem to be made for cold-water supplies. Does anyone have experience with models that turn off once hot water is being supplied?
posted by odinsdream at 5:21 AM on January 24, 2011

Maybe you can find a model with a digital thermostat that allows you to set the actual output temperature. Then you could set that temperature a few degrees lower than the incoming hot water, so when the hot water reached it it would turn off.
posted by 6550 at 3:00 AM on January 25, 2011