Shower Hot Water booster

FloridaCliff · February 04, 2012, 05:59:49 AM

Just curious!

Has anyone used a block heater like this as a booster on any hot water line.

I was thinking this might give someone with a slightly undersized water heater the help it needed.

Could be on its own circuit, and switched in and out hour before shower time?

Maybe not designed for it , but?

http://www.amazon.com/Hotstart-TPS151GT10-000-Engine-Coolant-Heater/dp/B0006NZQQ4

Cliff

Sean · February 04, 2012, 09:19:17 AM

It will not work for that application.

This unit is designed to circulate the coolant by convection, which is very, very slow. Moving water past its 1000-watt element at 2-3 gpm (the flow rate of a typical shower), the water will hardly be in contact with the element long enough to get any heat at all. I don't think you'd even notice it.

Here is some quick back-of-the-envelope math:
1,000 watts is 3,412 BTU per hour. A BTU is the amount of heat required to raise one pound of water one degree Fahrenheit. Let's say your shower uses 2 gpm. A gallon of water is roughly 8.33 pounds, so that's 16.66 pounds per minute. 3,412 BTU/h could raise this 16.66 pounds of water a whopping 204.8 degrees in a full hour, but in one minute that's only 3.4 degrees. So if water comes out of your water heater at 110, this would raise it to 113.4.

The numbers get worse if your shower flows more than that. At 3 gpm, this will raise the temperature only 2.3 degrees.

To top it all off, it won't work at all above 120, so if your water is already hotter than that, as would be true for many RV water heaters, it's just an extra restriction in the line.

-Sean
http://OurOdyssey.BlogSpot.com

FloridaCliff · February 04, 2012, 10:24:28 AM

Sean,

Thanks for the reply!

I had gotten all excited about the 1500 watts and failed to consider the gpm passing through them.

The devils always in the details....

The only good part for me is I bought them for 90% off Amazon's price.

Cliff

robertglines1 · February 04, 2012, 07:36:59 PM

Cliff : if you had a small 2 or 3 gallon tank close by and heated it that would work Simple flow switch could activate it like a hot tub switch or you could just kick it on just a few minutes before use and use thermostat off old hot water heater.. See you soon heading your way in a few weeks. Bob

FloridaCliff · February 04, 2012, 08:10:28 PM

Hey Bob,

Looking forward to seeing You and your Bride.

Have a safe trip South.

Cliff

JackConrad · February 05, 2012, 04:48:52 AM

Quote from: robertglines1 on February 04, 2012, 07:36:59 PM
See you soon heading your way in a few weeks. Bob

Bob,
We will be heading to Ocala area in about 10 days for our annual trip to a private bluegrass jam. We will be in the area until mid March. Would like to see you before we head further north. Jack

robertglines1 · February 05, 2012, 07:31:07 AM

Will pm everyone as to visits; great. As to subject: have thought about Cliff idea before after working on our hot tup heater/tank set up. If you raise water temp 10 degree that's 10 degree less hot water you need to mix and prob 30% less you need to use.(of stored hot water) I think 10 degree would be minimun in 2 gal tank over a slow flow rate of mixed water shower flow. Outside the Box Cliff!!!!! Proud of you Bob By the way you sure can tell hotter water flowing out the jets on our 8 person hot tub and the tank on it is about 2 gal.

Dreamscape · February 05, 2012, 07:41:10 AM

I'm curious, has anyone tried this?

http://www.hotwaterlobster.com/index.html

Hot Water Lobster Information Commercial 111215-15s

luvrbus · February 05, 2012, 07:56:34 AM

That is a mixer Paul they work as long as you have hot water,I don't understand why Cliff's idea would not work the supplemental heating on different systems like AquaHot use almost the same setup ?

Sean · February 05, 2012, 08:06:49 AM

Quote from: Dreamscape on February 05, 2012, 07:41:10 AM
I'm curious, has anyone tried this?

http://www.hotwaterlobster.com/index.html

We have a different solution to that problem.

The lobster and other similar valves have a serious downside if you do a lot of boondocking as we do, and don't run the water heater full-time. Once you have a tankful of hot water, over time, this type of valve will essentially completely empty the tank of hot water, even when you are not using any. By contrast, when we pull into a parking spot at, say, 3pm with 12 gallons of 170° water that was heated, for free, by the engine, I still have plenty of hot water to take my shower at midnight or 1am.

Our solution requires an extra water line from each fixture back to the fresh tank. When we want to use hot water, we open a solenoid valve at the fixture which allows the hot water to flow from the tank, all the way to a tee at the fixture, then by means of the extra line back to the fresh tank. It only takes a few seconds to get piping hot water this way, and we don't waste a drop of fresh water or gray tank space. The water in our well-insulated water heater stays hot for hours, and if we drive every day, we never have to heat water with either the Webasto or generator. When we are parked for several days, we get all the hot water we need each day by running the generator for half an hour or so.

If you mostly stick to camp sites with electrical hookups, then these household style valves do work as promised to get you faster hot water, at the expense of luke-warm cold water.

-Sean
http://OurOdyssey.BlogSpot.com

Sean · February 05, 2012, 08:17:41 AM

Quote from: luvrbus on February 05, 2012, 07:56:34 AM
... I don't understand why Cliff's idea would not work the supplemental heating on different systems like AquaHot use almost the same setup ?

The difference between this device and an AquaHot is that the AquaHot has a large thermal mass and a very long (coiled) heat exchanger tube. So the fresh water is in contact with a larger heat source for a longer period of time as it passes through the system. With a 1000-watt heating element, though, an AquaHot could not deliver "unlimited hot water" because eventually the cold fresh water passing through it will deplete the thermal mass, faster than the 1000-watt element could reheat it.

For most purposes, such as a shower, there is enough thermal mass in the tank to do what's needed, and then the electric element can make it up over a longer period of time by reheating the thermal mass (coolant) in the tank. BTW, one of the complaints I hear from AquaHot owners is that the system just can't keep up with much demand when run on electric element only. Elsewhere on the board there was a thread about changing to a larger electric element because of this.

The device at the top of this thread is not made for an open system with fast-flowing water. It is made for a closed-loop system where the only flow is by convection. It has all the time in the world to slowly heat the few gallons of coolant that are in the engine. (It does not need to heat the coolant in the rest of the cooling system because it operates at a temperature lower than the thermostats).

-Sean
http://OurOdyssey.BlogSpot.com

boogiethecat · February 05, 2012, 09:08:10 AM

I have to disagree with Sean on this one... back in my Ren-faire days we used to gravity feed water from a storage tank through one of these block heaters (also 1,500 watts) into a small shower head with a valve. We'd run the block heater with a 3K honda generator. It made a nice shower... not forceful mind you, but more of a trickle-style 2-3 gallon water-conserving camp shower... slow it down with the valve and get warmer... it worked really well. As I said it wasn't forceful in the slightest but it did make the water warm enough to take a shower, and you did get clean.

Later on we changed the system over to a small water-to-water heat exchanger installed in a step-van's cab heater loop. Start the van and let it idle for 5 minutes or so 'till the engine warms up, run tap water thru the exchangers' isolated side and into the shower head, and from that point have virtually unlimited hot showers (well until the van ran out of gas

. We'd run the thing and have a line of 20 people waiting to enjoy the nice hot showers!

Sean · February 05, 2012, 11:14:08 AM

Quote from: boogiethecat on February 05, 2012, 09:08:10 AM
... we used to gravity feed water from a storage tank through one of these block heaters (also 1,500 watts) into a small shower head with a valve. ...

Gary, the unit being discussed is only 1000 watts, not 1500.

With a 1500-watt unit and a very low flow rate such as you would get with the small, gravity-fed shower you described, yes, this could work. My math was for a 1000-watt unit and conventional pump-fed household shower running 2-3 gpm, which is what I would presume the OP was thinking of using.

Re-doing the math at 1500 watts and, say, 1 gpm, you would have a 10.5° temperature rise. If you started with a bag or bucket of water at an ambient temperature of 75°, that would give you an 85.5° shower, which would probably feel acceptable under the circumstances. Slowing the flow rate down even further would, of course, give you even warmer water.

-Sean
http://OurOdyssey.BlogSpot.com

FloridaCliff · February 05, 2012, 12:36:11 PM

Quote from: Sean on February 05, 2012, 11:14:08 AM
Quote from: boogiethecat on February 05, 2012, 09:08:10 AM
... we used to gravity feed water from a storage tank through one of these block heaters (also 1,500 watts) into a small shower head with a valve. ...
Gary, the unit being discussed is only 1000 watts, not 1500.
-Sean
http://OurOdyssey.BlogSpot.com

Sean,

The unit is 1500 watts. When you click on the link it shows a 1000 watt below the actual unit, easy to confuse.

Cliff

Sean · February 05, 2012, 01:59:25 PM

Quote from: FloridaCliff on February 05, 2012, 12:36:11 PM
... The unit is 1500 watts. When you click on the link it shows a 1000 watt below the actual unit, easy to confuse.

Ah, OK -- I was reading the spec on the link, so I've been using 1000 watts for the math.

At 1500 watts, with a 2gpm flow rate you'd get about 5 degrees. At a 3gpm rate, you'd get about 3.5 degrees.

-Sean
http://OurOdyssey.BlogSpot.com