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This question is a follow-up to It takes a minute or more for the water to become hot from any of the faucets in my house -- how can I speed this up?.

I have a tankless water heater, and it takes over 90 seconds to get hot water to my kitchen. (This is not acceptable as I'm not renting out this property.)

I'd like to install a "unit" close to the kitchen faucet. Ideally, this unit would not store water, but would heat the water as it passes through. This way, when the hot water finally reaches the sink from the main water heater, the local unit could stop working and let the main water heater do the work.

But, as I type this, I'm thinking that this may not be the ideal solution. The problem is that, to get hot water, the sink has to be turned on full blast (to trigger the water heating mechanism in the tankless water heater). So maybe I should have a 5gallon water heater near the kitchen sink to handle all hot water that the kitchen sink will need. If I went this route, would the kitchen sink ever be able to use hot water from the main hot water heater? Put another way, would turning the hot water on the kitchen sink on full blast trigger hot water to come from the main water heater?

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Do you want to use propane/natural gas or electricity? Can you supply a high-current circuit to the sink area? –  Jay Bazuzi Jul 13 '11 at 5:57
    
I'm pretty sure I'd like to use electricity as that seems like the easiest way to go. I'm not sure if I can get a high-current circuit to the sink area. –  three-cups Jul 13 '11 at 14:32
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1 Answer

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The wait time to get hot water from a tankless heater is very common, especially when installed some distance from the faucet. The specs for different heaters varies as far as the volume needed to trigger to on. Most do not require full flow volume to turn on.

There are a few small point of use tank heaters, such as American Water Heater Company's Titan series (Lowes) that only store 2.5 gals of water and operate on 120VAC. You should have a separate 120 volt circuit for this type of heater however.

Keep in mind, 2.5 gals is a lot of water in one use, unless you tend to run hot water for longer periods of time. Your main tankless will deliver hot water to the small tank heater by the time temps drop in the small tank, theoretically the small heater will not need to turn on and the hot water will simply pass through.

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instead of only taking care of the kitchen sink (yes, that is the problem area in this particular situation), would it not be better to invest the time & money into installing a small (5-10 gallon) hot water storage tank into the existing hot water system? That way the complete hot water system benefits from the upgrade (money sent). –  Mike Perry Jul 13 '11 at 15:11
    
The idea is that the source of the hot water gets closer to the faucet from which you want hot water. Water sourcing pipes are laid out in a tree-like structure; there's a main water "trunk" from the outside, with a major "branch" to the HWH, then both of those spawn other "branches" that feed bathrooms, kitchens, outside faucets, etc. By installing an "inline" HWH on any given branch, you reduce the time needed to flush out water in the hot line which has cooled. But, that won't help any other branch; water won't "backflow" from a branch back to the trunk. –  KeithS Jul 13 '11 at 16:43
    
So, no, adding just one more tanked HWH won't help the entire system, other than providing a larger overall hot water reservoir. For faster response, you need several "point-of-use" systems which either provide a reservoir of hot water nearby or actively heat water flowing through the line right before it comes out the faucet. –  KeithS Jul 13 '11 at 16:45
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I think the question really is asking about the kitchen, as this faucet is the most common use of frequent, short hot water uses. Many of my customers have had the same reaction to a central tankless unit if installed too far away. But even the best units need about 10 t0 15 seconds to start producing hot water. The small gallon to 2 gal units are relatively cheap and solve the problem of frequent short hot water use, especially when installed right under the kitchen sink. Most other rooms don't have the frequent use of a kitchen and folks accept the wait. –  shirlock homes Jul 13 '11 at 20:43
    
@KeithS & @shirlock homes, I believe I may not have set out my initial question very well. I was wondering (I don't even know if it's possible, hence me asking), is it possible to add in a (small) Hot Water Storage tank into a Tankless Water Heater system, thus creating a Hybrid Water Heater type system? –  Mike Perry Jul 14 '11 at 14:01
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