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02-06-12, 10:36 AM | #1 |
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tankless water heater questions
does anyone know about rheem water heaters? I am looking at an rtg-64xn outdoor tankless water heater. seems like a good unit. My one question that I cant figure out for sure is if it senses incoming water temp and adjusts on its own. would it sense water temp around 90 to 100 in case I do get around to building my solar water heater?
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02-06-12, 10:57 AM | #2 |
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Well I am not speaking for this model, but I am pretty sure that all of the big name companies water heaters work like that. I have a navien and it does, my friend has a rheem (indoor) and it does too.
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02-06-12, 11:56 AM | #3 | |
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Quote:
I have checked out quite a few less expensive Chinese units, and virtually none of them sensed incoming or out going temperatures. I know that there are models made by various manufacturers, that are meant for solar applications. There are also models that are meant for hydronic water heating applications. I do not know if units meant for hydronics will also work for solar applications. When I bought my tankless unit, Bosch made models that would sense incoming water temp, and others that did not... It is in your interest to find out about the exact model you are interested in, and not hope that it might possibly work the way you want it to. It is your money, after all. -AC_Hacker
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02-06-12, 12:19 PM | #4 |
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After reading the specs on their website, I would have to say that it does "sense" the incoming water temperature.
TYPE GAL PER MIN. MODEL NUMBER ENERGY FACTOR ENERGY STARŪ Indoor Direct Vent 6.4 gpm at 35° F rise 5.6 gpm at 45° F rise RTG-64DVN Outdoor 6.4 gpm at 35° F rise 5.6 gpm at 45° F rise |
02-06-12, 12:36 PM | #5 | |
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Quote:
There is nothing in these numbers that indicates that the unit has the ability to sense incoming or outgoing water temperature. If you want to use this unit for solar in the future, it is in your interest that you find out for sure that this model will actually function for solar applications. It is your money you are about to spend. -AC_Hacker
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02-06-12, 12:58 PM | #6 |
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Hmmmm. I guess I misunderstood it then. I also read that it does have a thermostat control.
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02-06-12, 01:29 PM | #7 |
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just called rheem. they said that the unit will only come on if there is a 35 degree difference in the water temperature. So if I have 100 degree water coming into the tankless heater the unit will only start if it is set at 135 degrees.
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02-06-12, 02:36 PM | #8 | |
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Quote:
Your target temp of your tankless should be the hottest temp you will want to use. For me it is shower water at 104F. For other people it could be different. Tankless heaters have a copper heat exchanger, and the water is heated in one pass. The lower heat you require, the less scale build up you will have in the heat exchanger and the longer the heat exchanger will last. With tank type heaters, the use is different, since there is a limited amount of hot water, it is heated to a higher temperature than required and then it is diluted with cold water, giving you in effect, more hot water. Solar water can come to you in a range of temperatures, from ground temperature to much hotter than you need for bathing (even over 160F), so you will need an automatic temperature control valve to protect anyone in your house who uses the water from scalding. And you will need a tankless that can handle much smaller delta T... like a few degrees or even less. Did you ask them if that Rheem will work with solar heated water as an input? * * * I have had a tankless, a Bosch 125X for about 15 years. It has been very reliable. I did have a problem with a transformer, after I had been using it for a month, and they sent me a new transformer, no charge, it arrived the next day from Pennsylvania. Tank type water heaters have improved a lot since I got my tankless, but I would probably stick with what I have. Tankless heaters have also gotten a lot better, too, with regards to efficiency, etc. I picked up another Bosch that is more efficient, in a garage sale for $35 dollars. I'm hanging onto it should I need to replace the one I have. I have heard a lot of complaints about Bosch service, but they did fine by me. Rinnai seems to have a good reputation. I don't know much at all about Rheem, one way or the other. No matter what you get, I would advise locating the water heater as close as possible to the most often used hot water outlet in the house. for me that is the hot tap in the kitchen. When ever I go to the new tankless, I may locate it on the wall, right over the kitchen sink. I think the outdoor models are a good idea, too. Good luck with your choice. -AC_Hacker
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I'm not an HVAC technician. In fact, I'm barely even a hacker... Last edited by AC_Hacker; 02-06-12 at 02:52 PM.. |
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02-06-12, 03:07 PM | #9 | |
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Quote:
I just got off the phone with them myself. If your incoming water was at 100 and you had the tankless set to output water at 135 then the tankless will only have to heat the water 35 degrees. It will only turn on 1 of three gas heaters to accomplish this. The colder the water the more heat needed to heat it to the set temp. If the incoming water is hotter than what you have the tankless set at, then it will not turn on. This tankless actually has a flowmeter to control the flow of water to keep it at the set temperature. So if someone flushes a toilet or turns on a faucet it will automatically adjust the flow to keep the water at same temp. I asked if it can sense the incoming water temp. She said it does. |
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02-06-12, 04:40 PM | #10 |
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I specifically heard from the guy that if there was not a 35 degree difference in water temp that the unit would not turn on. However I would not be surprised if he was wrong. Looking at the min BTU rating this unit has actually the lowest rating on the low side. I went ahead and ordered this unit because I think it is all around the best one for my need. even if it isnt the best for the solar application it will work and its fairly reasonably priced plus i can link up to 20 in the future as my family grows. If in 10 years i have two teenage girls who have more water requirments than i do I can buy another unit and link them up. This unit also has the lowest required flow to turn on the system. I think for the price it will work just fine. Maybe there is a 35 degree requirment to turn on. I think even with that I could make it work. Ideally the tankless would be on backup only duty and if I did run out of solar hot water I would have to adjust the valves a bit to get the correct temperature. I can live with that.
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