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tony

Oct 17, 2010, 7:52 PM

Post #1 of 9 (1460 views)

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On Demand Water Heater Capacity

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Hi,
I have a 5 liter/minute on demand gas water heater that can't keep up with me taking a shower. Can anyone tell me if this if I need to increase the heater capacity or look into the plumbing.

I am not using pressurized water.

Thanks, Tony

"We don't see things as they are, we see things as we are."

Grevo

Oct 18, 2010, 8:32 AM

Post #2 of 9 (1435 views)

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Re: [tony] On Demand Water Heater Capacity

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Hi Tony,

First I wrote a general article about these issues in the following article on Mexconnect:
http://www.mexconnect.com/articles/2951-water-heaters-in-mexico

From the users point of view, the demand style heaters function very differently from the tank style heaters. When using the tank style heater it is very common to adjust the temperature in a shower using the hot and cold water valves.

But for a demand style heater it is better that first to turn on the hot water not to full flow but to approximately half flow. Let the water get very hot and then turn on the cold water to cool down the water in the shower. Now it may be obvious to state but use only the cold water to adjust the temperature; more cold water to cool the water and less cold water to make the water hotter. By changing the hot water flow may cause the flow rate through the demand heater to exceed the capacity of the heater and the hot water will cool down.

The typical flow rate in a shower is between eight to twelve litres per minute and assuming a 50/50 shared flow rate between the cold and hot water. Hence your heater with a capacity of five litres per minute is at the middle to lower range needed for a shower but should be sufficient for a good shower not a super hot shower. The five litre per minute is lower than I recommend for a house (eight litres) but it is the minimum needed. Of course, with a five litre per minute heater, it would be impossible for two people to have a shower (independently) at the same time. Then again, it is motivation to have two people share the same shower to conserve hot water ;)

It can also be a problem for some appliances. Depending on the flow to the appliance, it may not be sufficient. For instance if the dishwasher needs to fill quickly, the flow rate may be faster than the heater can produce. The clothes washer may not be able to fill quickly for a hot water load but may be sufficient for a warm water load.

Good luck and I hope this helps you to enjoy your shower more.

-------------------------------------------------
Sin Compentencia tenamos Incompentencia!

gpkgto

Oct 18, 2010, 9:15 AM

Post #3 of 9 (1428 views)

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Re: [tony] On Demand Water Heater Capacity

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Grevo is obviously the expert, but my problem with the de paso heater was that my bathroom was more than 5 meters from the heater and the hot water just couldn't get there. I had to go back to an old style boiler.

johanson

Oct 18, 2010, 12:56 PM

Post #4 of 9 (1410 views)

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Re: [gpkgto] On Demand Water Heater Capacity

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I'm confused by your distance comments. I'm ten meters or more away from the instant on heater, which by the way I have never had to turn on, because I use solar panels and the water coming there-from is more than hot enough for a warm shower, even after a cloudy day followed by a cold night.

Now downstairs, I have an instant on hot water heater where the shower is again more than ten meters away, and the instant on system which is on downstairs, works just great, and we even have the heat turned low thereon. Of course when they installed the hot water lines, I had them put insulation around them, which makes things a little better.

Also the instant on hot water system has a very small water storage tank. No, sadly, I don't remember the capacity of any of the equipment

gpkgto

Oct 18, 2010, 2:29 PM

Post #5 of 9 (1398 views)

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Re: [johanson] On Demand Water Heater Capacity

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I am no expert, but I tried 2 different de paso water heaters (with no pressure pump--maybe that was the real problem) before a plumber told me the distance was the problem. I have a one-storey house with pretty low water pressure.

johanson

Oct 18, 2010, 4:30 PM

Post #6 of 9 (1382 views)

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Re: [gpkgto] On Demand Water Heater Capacity

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I have a pressurized water system in my house. I am not sure how that helps, but it must. And again, I stress, my architect insisted that I insulate my hot water lines, and, of course, I did. And all works great. But I'm not sure why :)

Peter

Oct 18, 2010, 4:44 PM

Post #7 of 9 (1380 views)

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Re: [gpkgto] On Demand Water Heater Capacity

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I put a de paso unit into my home some three years ago and never had problems with getting sufficient hot water or passable pressure for an unpressurized system that fed a second-floor casita above my cochera - the water heater being located on the ground floor.

Later I added new construction in back of my lot with a shower at the extreme back end on the ground floor some 15 meters away from the heater before adding in the extra line to travel up then back down again. I gained extra water pressure and receive the hot water in that shower in very short time.

Now I have done extreme remodelling and new construction relocating my tinaco on top of a thrid-floor wash house and put that same de paso unit inside the wash house which adds a few more meters of travel. This was just completed this past Saturday and I know my water pressure is fine and I should be getting some information on the hot water situation from a friend who is staying in the home during this construction while I am renting elsewhere temporarily. I will report on that when I have some data.

The de paso system is no energy saver but that is not the idea for putting there. Its advantage, of course, is that it gives me continual hot water as I desire it and has done so through some 17 meters or more of copper pipe. It will now have more travel and be servicing three showers but will still be a couple months or more until all of us once again reoccupy the home. I am curious to see if I have gone beyond its limits for good service now but up to this change it seemed it still had much more to give. Interest is up so I will report back after trying to stress its capacity to service the home.

(This post was edited by Peter on Oct 18, 2010, 4:47 PM)

johanson

Oct 18, 2010, 6:17 PM

Post #8 of 9 (1370 views)

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Re: [Peter] On Demand Water Heater Capacity

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Remember to put insulation around the hot water pipes. It makes all the difference in the world, especially when the shower is not close to the instant on heater.

Peter

Oct 18, 2010, 6:42 PM

Post #9 of 9 (1365 views)

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Re: [johanson] On Demand Water Heater Capacity

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Thanks. That seems like good advice, especially now that I have so much more exposed pipe than before.