Under-Sink Mini-Tank Water Heater

[TromboneAl]

Having a mini-tank water heater under the sink looks like it will be a perfect solution to the problem of waiting for hot water. I've calculated that I must run 1.5 gallons of water before it reaches full heat. If I have a mini-tank heater, then that will supply the hot water in the interim. Also, that tank will then receive the hot water from whole-house heater, and be ready to go again at any time.

However, the problem I see is fitting one in there. Here is my undersink area:

And this product is 11x14x14.

Is there some way to make this fit (reroute plumbing), or should I try to find a smaller model? Note that I will be getting a single bowl sink, with the drain on the left.

 

[pb4uski]

This would fit better in the space and is tankless. But will your undersink 120 service support it (It requires 20 amp with 12 ga wire)?

I think your best bet would be mini-tank or tankless units that will fit better in your cabinet. I'll be going through the same process soon. I'm sick of waiting for hot water to get to the sink from the utility room.

 

[HFWR]

When you say single bowl, do you mean one sink as wide as the two you have now? If the single bowl is the size of one side now, why not install on the right side, get rid of the disposal (use it's power for the heater), since your p-trap and drain are already on the right. Should leave plenty of room, assuming your sink base is 36".

 

[pb4uski]

Would it fit along the left wall of the cabinet? or would it conflict with the disposal?

Or could you reconfigure the disposal to be on the right sink to free up some room on the left side of the cabinet for the HW unit?

I just saw your note that your are going to a single bowl sink. If you could concentrate the drain and disposal on the right side of the cabinet then you would free upspace on the left side for the HW heater.

The constraint is the location where the drain enters the wall.

 

[martyb]

Do I see six beers under your sink?

We just bought our retirement home, and our kitchen sink is a long way from the water heater (in the attic). I haven't thought about checking to see how many gallons of water we're wasting before the hot water gets to the tap, but I'll do that. I've considered doing what you're talking about.

 

[HFWR]

Do I see six beers under your sink?

They stay colder in the fridge...

 

[travelover]

I don't recall if you have a basement, so this might not be practical. I have a hot water return line from my farthest faucet T'd into the drain valve on the water heater. I get instant hot water at the small cost of the constantly circulating water's heat loss. Seems like Pex would be great for a retrofit.

 

[TromboneAl]

A tankless would probably require rewiring, and doesn't have the nice plays-well-with-other-heater attributes. I could do that if necessary.

Yes, the single-bowl sink is as wide as the current sink, and has the drain on the left, and I have no choice there (unless I want the faucet in the front).

Do I see six beers under your sink?

Those are actually emergency seltzer water cans. If someone spills wine on the carpet, I grab one and empty the entire contents onto the spill.

 

[Bob Adams]

Grundfos has a slick product available that you might not have ran across before. Works well and Grundfos is a top notch manufacturer. Minimal space required and the only electrical connection required is for the circulation pump, and that's just 115VAC.

Grundfos Comfort System | Grundfos

Good luck!

 

[pb4uski]

These look interesting. Small size.

Mini Tank | Waiwela

Also this one would seem to fit your space - it may be the leading contender for my application.

http://www.amazon.com/Rheem-81VP2S-...=point+of+use+hot+water+heater#productDetails

 

[painterbill]

Reroute the plastic drains within the cabinet would be the easiest solution to gain the needed space. With a few fittings you could move the trap parallel to the back of the cabinet and route the drain from the right hand sink right out of the basket to the back of the cabinet to gain the needed space on the right hand side of the cabinet. When you put your new sink in you can change and pretty up the drain installation permanently.

 

[Telly]

Having a mini-tank water heater under the sink looks like it will be a perfect solution to the problem of waiting for hot water. I've calculated that I must run 1.5 gallons of water before it reaches full heat. If I have a mini-tank heater, then that will supply the hot water in the interim. Also, that tank will then receive the hot water from whole-house heater, and be ready to go again at any time............

It will be interesting to see how this works out. After first turning on the faucet, hot water will come out, as it is heated water off of the top of the mini-tank. As the hot water continues to be taken out of the top of the tank, cool water from sitting in the pipes will be filling into the bottom of the mini-tank, eventually going out the faucet. As the inlet water into the mini-tank rises in temperature due to the main water heater, the water in the minitank will increase in temp. Then all the water coming out of the faucet will be hot, from the main water heater.

So it would seem if the mini-tank's capacity is less than some X times of the amount of the "slug" of cold water due to sitting in the pipes cooling off from the main heater, then the faucet water temperature profile versus time will be:
Hot -> Cold-> Hot

If the mini-tank's capacity was many times the amount of the slug, then it would seem that even with cold pipe water mixing in for the short while, there would be enough hot water stored in the mini-tank to mix in with and minimize the cooling effect of the input slug.

I'm just thinking as I'm typing...

 

[pb4uski]

It will be interesting to see how this works out. After first turning on the faucet, hot water will come out, as it is heated water off of the top of the mini-tank. As the hot water continues to be taken out of the top of the tank, cool water from sitting in the pipes will be filling into the bottom of the mini-tank, eventually going out the faucet. As the inlet water into the mini-tank rises in temperature due to the main water heater, the water in the minitank will increase in temp. Then all the water coming out of the faucet will be hot, from the main water heater.

So it would seem if the mini-tank's capacity is less than some X times of the amount of the "slug" of cold water due to sitting in the pipes cooling off from the main heater, then the faucet water temperature profile versus time will be:
Hot -> Cold-> Hot

If the mini-tank's capacity was many times the amount of the slug, then it would seem that even with cold pipe water mixing in for the short while, there would be enough hot water stored in the mini-tank to mix in with and minimize the cooling effect of the input slug.

I'm just thinking as I'm typing...

Interesting thought. I think you may be right in that once one turns on the faucet the water would probably go hot then cold or warm and then hot so it may not "solve" the problem but rather just defer the problem. The question would be what "x" needs to allow the mix of hot water from the mini and water from the main heater to not become too cool.

I've heard of tankless HW heaters being used in such situations and it is clear that those would work and then would turn off once hot water from the main heater reaches the tankless.

 

[zinger1457]

Are you doing this to conserve water or save money? If it's to save money I doubt you'll ever re-coop the cost of whatever system you choose. As a water conservation measure recirculation pumps are now part of the building code for new home construction where I live in Arizona.

 

[calmloki]

Grundfos has a slick product available that you might not have ran across before. Works well and Grundfos is a top notch manufacturer. Minimal space required and the only electrical connection required is for the circulation pump, and that's just 115VAC.

Grundfos Comfort System | Grundfos

Good luck!

I think this is the hot ticket - hot water pretty much instantly at ALL points for the cost of keeping hot water in the pipes and some minimal pumping. Wonder if the cost isn't equal to the cost of having a couple gallons of hot sitting under the sink in a poorly insulated container. It was suggested to me when we did our place a dozen years ago - didn't do it, I just adjust what I'm doing to match the temperature changes.

 

[pb4uski]

Just thinking some more. I wonder if one could solve the hot>cold>hot problem of a mini-tank by plumbing the mini-tank and the hot water line from the main hot water heater into some sort of valve that would mix the hot mini-tank water with the room temperature lag water until the main hot water reaches the sink. Any plumbers out there?

 

[pb4uski]

I think this is the hot ticket - hot water pretty much instantly at ALL points for the cost of keeping hot water in the pipes and some minimal pumping. Wonder if the cost isn't equal to the cost of having a couple gallons of hot sitting under the sink in a poorly insulated container. It was suggested to me when we did our place a dozen years ago - didn't do it, I just adjust what I'm doing to match the temperature changes.

I agree but my main system is a propane fired tankless so a recirculation solution wouldn't work for me as the tankless would be running all the time.

 

[calmloki]

I agree but my main system is a propane fired tankless so a recirculation solution wouldn't work for me as the tankless would be running all the time.

Ahh. We've nat gas water heater in a remote location - even have a 110V outlet right there by the top of the tank waiting for me. Don't recall if T-Al is tankless - don't think so if I recall a thread from long ago about running pipes from a garage location and floor joists....

 

[Texas Proud]

A tankless would probably require rewiring, and doesn't have the nice plays-well-with-other-heater attributes. I could do that if necessary.

Yes, the single-bowl sink is as wide as the current sink, and has the drain on the left, and I have no choice there (unless I want the faucet in the front).



Those are actually emergency seltzer water cans. If someone spills wine on the carpet, I grab one and empty the entire contents onto the spill.

If you go to the 'insta-hot' (tankless), you can close off the hot water line and just split the cold... no need to draw any hot water from the big tank....

 

[walkinwood]

We have the grundfos comfort system, but to back-fit it into an existing home, you'll need to make a change to your piping - something called a direct return.

I've seen other hot water circulators that only need a minor modification under the sink - the hot water is dumped into the cold water pipe when the circulator is on. These also have a switch at the sink so you can turn it on just when you need it.

Our hot water cirulator has a timer so it can be set to turn on at certain times. That doesn't work well for us since we don't have a fixed schedule. I'm thinking of buying a remote controlled switch so we can turn it on/off when we need it. Still looking for the ideal switch - remote on/off with a timer in case we forget to turn it off. I've seen one by NuGiant that looks interesting.

 

[ERD50]

...

So it would seem if the mini-tank's capacity is less than some X times of the amount of the "slug" of cold water due to sitting in the pipes cooling off from the main heater, then the faucet water temperature profile versus time will be:
Hot -> Cold-> Hot

If the mini-tank's capacity was many times the amount of the slug, then it would seem that even with cold pipe water mixing in for the short while, there would be enough hot water stored in the mini-tank to mix in with and minimize the cooling effect of the input slug.

I'm just thinking as I'm typing...

Agreed. I would expect the temperature of a small tank to drop pretty quickly as the cold water mixes. You get significant stratification in a large tank, very little in a small tank like that, with those kinds of flows.

Are you doing this to conserve water or save money? If it's to save money I doubt you'll ever re-coop the cost of whatever system you choose. ...

This too. I sometimes think of doing something like this in our bathroom, and like pb4uski mentioned, it could be improved with a mixing valve (you could keep the little tank set at a higher temp, therefore increasing its effective capacity).

But then I think abut all this, and I decide that occasionally waiting a minute for some hot water isn't really that big a hardship.

-ERD50

 

[pb4uski]

....But then I think abut all this, and I decide that occasionally waiting a minute for some hot water isn't really that big a hardship....

True, its in the "nice problem to have" category in the whole scheme of things, but in my case we also have a well and septic system so the water that flows into the drain while i'm waiting for the hot water to arrive is coming from my well (no big deal since I have plenty of water) and going into my leachfield (could be a bigger deal at some point).

 

[Bob Adams]

We have the grundfos comfort system, but to back-fit it into an existing home, you'll need to make a change to your piping - something called a direct return.

Grundfos makes them for either new construction with a return line, or existing construction where the existing cold and hot water lines are used. The product number for existing construction is 595916 and can be seen here on Amazon Grundfos 595916 1/25 Horsepower Comfort Series Recirculator Pump - Amazon.com

 

[Bob Adams]

I think this is the hot ticket - hot water pretty much instantly at ALL points for the cost of keeping hot water in the pipes and some minimal pumping. Wonder if the cost isn't equal to the cost of having a couple gallons of hot sitting under the sink in a poorly insulated container. It was suggested to me when we did our place a dozen years ago - didn't do it, I just adjust what I'm doing to match the temperature changes.

Exactly, hot water everywhere, extremely compact, not much if any parts needed to install, and simple enough to do so that you can eliminate the high priced labor.

 

[TromboneAl]

New sink in, plenty of room for a mini-tank now:

My measurements show that I get hot water from the whole-house heater after 1.5 gallons flow through the faucet. So, for the first 1.5 gallons, I'll get hot from the mini, then from the main. When done, the mini will have hot water in it, so it will never have to heat up cold water.

I'm starting a new thread to get advice on which one to purchase.