Point of use hot water heater?

[Matt Meiser]

My shop has a frost free hydrant which I have hooked up to a "sink" via a hose. It is really nice to have running water in the shop, but that water is COLD this time of the year (no complaints in the summer.) Someone told me today about a 2.5 gallon HW heater that plugs right into the wall. Looks interesting, but I'm wondering about efficiency and recovery time on them? I'm wondering if I could put it on a switch and just turn it on when I'm in the shop and still get hot water quick enough. There are tankless units as well but they are much more than the 2.5gal at Menards for $150.

[Al Willits]

Tankless is not only spendy to buy, but a lot more involved to install and maintain.
One question would be, how much water will you need at one time?
I don't know but I wouldn't think recovery rates would be to bad considering its only 2.5 gals, possibly the water heater has that info.
Or your electric company may be able to tell you how many watts it takes to heat a gallon of water.
Al

[Brian Elfert]

I did some research on those little tankless heaters a while back.

They would most likely work for a sink in a shop, but they won't work for a shower or tub for sure.

Brian Elfert

[Matt Meiser]

Tankless is not only spendy to buy, but a lot more involved to install and maintain.
One question would be, how much water will you need at one time?
I don't know but I wouldn't think recovery rates would be to bad considering its only 2.5 gals, possibly the water heater has that info.
Or your electric company may be able to tell you how many watts it takes to heat a gallon of water.
Al

I looked through the manual on one at Lowes and there wasn't much information. Basically all it said is that it had a 1350W element, but no mention of how long it would take to heat the water, etc. I would only use a small amount of water at a given time--just hand washing and doing "dishes" (spray gun parts, glue bottles, etc.)

What I'm wondering is if I could just turn it on when I'm in the shop and have hot water by the first time I get my hands dirty.

[Ken Garlock]

Hi Matt. Installing a tankless electric is no big deal.

1) plumb it in under the sink.
2) Run recommended size electric cable.
3) turn it on.

I bought a 36 KW model from this company (http://www.hotwaterheater.com/model-h-14-2.htm).

[Phillip Thorne]

if it's a 2.5 gal tank w/ a 1350w element, given that 1350w = 4609 btu/hr and 2.5 gal of water weighs 8.33lbs

it should raise the water temp one degree every 22 minutes or so

so to raise the temp by 25 degrees it'd take 9 hours

if i did the calculating correctly (feel free to correct ;-) )

[Al Willits]

One gallon weighs 8.33 not 2.5 gals.
Also wondering what operating cost would be to just leave water at say 138 or so degree's all the time, might be easier
Also you didn't say elect or gas on the tankless and I of course figured gas....being as I work for a Nat gas supplier....:)
Al

[Phillip Thorne]

that's why i edited it, i changed the time calculations...

[Matt Meiser]

It would be electric. We have propane and I definitely don't want to deal with running a gas line 40+ feet.

For those in the know, how does recovery rate relate to heating a tank full of cold water from a dead start? I found some information here (http://www.plumbingsupply.com/ariston.html) on a very similar looking unit that says it has an 8gal/hr recovery rate at 90 degree rise?

Edit: Looks like Ace has an even better deal on the 2.5Gal units. Link (http://www.acehardware.com/product/index.jsp?productId=1276467&cid=). And apparently this particular brand is made by Bosch which leads me to believe they are a quality product (But then so is Skil.)

[Ken Garlock]

Let's look at it another way.

The heating element generates 4609 BTU in one hour.

2.5 gallons of water weighs 8.33 x 2.5 = 20.825 pounds

One BTU will raise the temp of one pound of water one degree F. Time is not a factor.

Using 1 hour, we insert 4609 BTU into 20.825 pounds of water.
That is 4609/20.825 = 221.32 degrees and the water boils away.

In one minute the temp is raised 221.32/60 = 3.7 degree per minute. This not good enough. With an on demand heater you need to heat the winter water, say from 40 up to 110, or a 70 deg boost. Assume you are using 2.5 gal per minute, you need to raise 20.825# of water by 70 deg per minute. (Remember new cold water is continuously entering the heater.) By multiplying the water flow in pounds by the temp requirement we get the number of BTUs needed per minute. 20.825*70 = 1457.75 BTU/Min.

Next convert that to watts. 1457.75*60 = 87465 BTU/Hr. Let us normalize to 1000 watt units. 4609/1.35 = 3410 BTU/ kilo watt hour.Now divide the requirement by the rate, 87465/3410 = 25.6 KW heating element required. This number roughly agrees with the sizes of electric demand heaters sold by the company I referenced above. To get that energy requirement they use two 12 KW elements where the water flows through the first element and then through the second.

To make Al happy;) . One cubic foot of natural gas contains 1015 btu. The calculation becomes much easier. 87465/1015 = 86.17 cubic feet per hour of gas, or 1.44 cuft/min.

[Brad Schmid]

Matt,
I'm not going to comment on specs... only on experience.

I have a small 6gal LP unit in my popup camper. That thing rocks! It will heat water from "dead cold" to "hot enough to burn your hand" in about 15 minutes. We use water for washing hands of course, dishes, showering, washing the dog, etc. in short-medium intervals like you are talking about. It does great. They also make these in an LP/elec combo unit.

[Al Willits]

"""""""
To make Al happy;) . One cubic foot of natural gas contains 1015 btu. The calculation becomes much easier. 87465/1015 = 86.17 cubic feet per hour of gas, or 1.44 cuft/min.
""""""""

No problems from me Ken, I run out of toes and fingers to keep up with all them numbers....:D

""""" an 8gal/hr recovery rate at 90 degree rise""""""""
This usually means that the unit will heat 8 gallons 90 degree's over inlet temp, in one hour....least I used to think so....:confused:

Considering I haven't a clue on instant elect water heaters, I'd want to know what electrical circuits I'd need, would a standard 20 amp 110 circuit handle one of these??
Just wondering, might be nice to know.

Al...who's going back to his dish....

[David G Baker]

It would be electric. We have propane and I definitely don't want to deal with running a gas line 40+ feet.

For those in the know, how does recovery rate relate to heating a tank full of cold water from a dead start? I found some information here (http://www.plumbingsupply.com/ariston.html) on a very similar looking unit that says it has an 8gal/hr recovery rate at 90 degree rise?

Edit: Looks like Ace has an even better deal on the 2.5Gal units. Link (http://www.acehardware.com/product/index.jsp?productId=1276467&cid=). And apparently this particular brand is made by Bosch which leads me to believe they are a quality product (But then so is Skil.)
Matt,
When I was in the Army and stationed in Germany back in the 60's I rented an apartment that had one of the electric point of use heaters. I think it held about 3 gallons. It was used to heat water for a bath tub. I never ran out of water and it was on all of the time so it had instant heat. It was very well insulated so I doubt that it consumed much electricity. I am sure the technology has improved since then.
Thanks for the idea, I was wondering how to get hot water in my pole barn.
David B

[Matt Meiser]

Matt,
When I was in the Army and stationed in Germany back in the 60's I rented an apartment that had one of the electric point of use heaters. I think it held about 3 gallons. It was used to heat water for a bath tub. I never ran out of water and it was on all of the time so it had instant heat. It was very well insulated so I doubt that it consumed much electricity. I am sure the technology has improved since then.
Thanks for the idea, I was wondering how to get hot water in my pole barn.
David B

The Bosch ones are Italian I think so they are probably pretty good efficiency-wise since that would be required over there. They just plug into an outlet for power. I also found them for $130 (with my Farm Bureau Member discount) at Grainger, and they stock them at the Ann Arbor location. LOML agreed with me getting one--in a few weeks since we need to pay off our Disney vacation and Christmas this pay period.

[Matt Meiser]

Update: I picked up the Ariston 4gal unit our local home improvement/gourmet food store for $129 last night. It was super-easy to install. It took about 2 hours including installing a new faucet since my old "faucet" was home made with a ball valve and some copper pipe. I was able to mount the hot water heater close enough to the sink that I could run the flexible hoses right from the water heater to the faucet. The cold water inlet just has a tee which supplies cold water to the faucet and the water heater and the hose from my frost-free hydrant attaches right there.

[Jim Becker]

Sounds good, Matt. The small point of use units work well and don't cost you much to run since they only use power when you are requiring hot water. I think it's a good choice for what you wanted to accomplish!

[Russ Filtz]

I looked into these for a small job at work. If you check into the ratings carefully, you'll find that a regular 120V model will not perform very well. You need to check the temperature rise ratings vs flow rate to get an idea of how hot the water will get for the instant flow thru models.

The 120V power only gives you a very small to modest temp rise = lukewarm water at best, esp in cold climates (remember the water coming out of the pipes will start colder in winter!). For washing hands, maybe lukewarm is OK, but for washing clothes or other uses?

I would go with a 240V model minimum. I think we even settled on a 277V one as we had the power handy.

[Matt Meiser]

This isn't an instant unit, but a small 4 gal water heater. Here's a generic picture of the one I got.

http://www.discounttankless.net/Merchant2/graphics/00000001/gl4_left2.jpg