At my wits end with tankless water heaters. Need help from those who use them.

[lighthousecarwash]

So I've posted a couple threads about tankless boilers for my floor heat and tankless water heaters for my auto, but I am still not sure I know which route to take. First of all, the floor heat is going to be on hold as I think it's getting too close to winter to start tinkering with floor heat. Here is my issue with the hot water and what my opinions are. Tell me if I'm on track or way off base.

1. I want to install a dedicated tankless water heater for my new Razor. I think this will be an easy fit because I can mount one of these units on the wall about 2 feet away from the pumping station. This should provide almost instant hot water to the auto. I'm looking at an AO Smith 540 (199,000 btu)unit that I believe is actually a Takagi. I have the option of adding a second Razor if this one gets too busy. I would put the second pumping station in the same vicinity of the tankless water heater. I'm hoping that by doing this, I can utilize the same tankless unit to feed both autos as it's only the solutions that will be hot and should not require that much GPM. I'm hoping for solutions around 120-130 degrees. The whole gray area with these things are the temperature rise and the GPM. With my current system with a boiler and 75 gal holding tank, none of that is a problem. I have ample reserve of hot water as the boiler catches up. So is a 6.6-10 GPM system enough to raise the temperature 70-80 degrees and not run out of water supply. If the demand is too much for the WH to supply that much of a temperature rise, then do I just get lower temperature water, or do I get lesser flow and still the same temp of water. I don't want to starve any pumps. What say you?


2. My self serve bays all operate out of a Magic Wand pump stand. This stand has a mixing tank for all the soap/wax solutions, and a clean hot water tank that feeds to pumps. Now my issue with this system is that the mixing tanks cool down over night and take a little bit of time to heat up once hot water starts flowing into them. With my 75 gal holding tank, there is still a delay in hot water getting to the mixing tanks. I've been told that if I eliminate my boiler, that I still need to have the 75 gal holding tank with the circulation pump to keep it heated. Why? If I place 2 of the above mentioned units, only a few feet from the mixing stand, then I should be achieving the same results. I would think a few seconds of flow and we would have instant hot water. Since I have the mixing tank with clear hot water, I shouldn't have an issue with starving the pumps because I would have 10-15 gals of hot water in that tank as a buffer. I have not done any calculations, but I think 2 units linked together should be able to support the 4 self serve bays. They will only be using hot water for the low pressure functions and the HP wax. I also was told we could go to a 6 gal holding tank and eliminate the 75 gal tank. That way we would have an instant reserve of 6 gals to get started when the mixing tank calls for water. But this would require the need for circulation pumps again, and heating that tank whenever it dropped below 115 degrees. I know I could use a timer and probably make that more efficient, but I don't think I even need it. Ok, help me out people. What do you use and how does it work for you?

In need of help!
Lighthouse.

 

[Eric H]

2. If I place 2 of the above mentioned units, only a few feet from the mixing stand, then I should be achieving the same results. I would think a few seconds of flow and we would have instant hot water. Since I have the mixing tank with clear hot water, I shouldn't have an issue with starving the pumps because I would have 10-15 gals of hot water in that tank as a buffer. I have not done any calculations, but I think 2 units linked together should be able to support the 4 self serve bays. They will only be using hot water for the low pressure functions and the HP wax. I also was told we could go to a 6 gal holding tank and eliminate the 75 gal tank. That way we would have an instant reserve of 6 gals to get started when the mixing tank calls for water. But this would require the need for circulation pumps again, and heating that tank whenever it dropped below 115 degrees. I know I could use a timer and probably make that more efficient, but I don't think I even need it. Ok, help me out people. What do you use and how does it work for you?.

I have a similar setup to this but using 2 199k btu Navian units. The system has more than enough capacity to provide hot water all day long BUT it simply does not work to supply the hot water holding tank. When the float valve drops the cold water in the pipe begins to fill the holding tank while the burner takes a few second to turn on. Then, by the time the hot water reaches the holding tank the float has already filled the tank part way. What ends up happening is that the 120º water that you are trying to get is diluted by colder water so you end up with 100º water and then by the time it gets out to the bays the water has lost a couple more degrees. Go with the 6 gal tank and a circ pump or the new Navian units have a small circulator pump in them that you could use and just add a 6 gal tank to the return line.
OR Check out this thread: http://www.autocareforum.com/showth...t-water-heater-with-tankless&highlight=navien Be sure to read 2biz's reply, it 's the third one. If I were to do it again this is the way I would do it!

 

[2Biz]

If you happen to read my post in Eric's link, I want to clarify something. When going the HTP route, I thought it would be necessary to have a heat exchanger in the hot water float tank. So I bought an expensive SS circulator, t-stat, and designed/made an elaborate copper heat exchanger. BUT I never installed it! It wasn't needed! CB80 suggested I was waiting my time and money....He was right! What I did do was insulate the hot water float tank with foil bubble wrap. At worst case....the hot water only cools off to the ER temperature and quickly recovers from there.

Another thing to consider..Most demand heaters restrict flow to obtain the desired output temp. My takagi 199k floor heater (supposed 10gpm) only puts out 6.6 gpm at only 30-40 deg rise. That's at 40 psi inlet pressure. Heating colder city water will cause your demand heater to perform even worse. Every manual has a chart that gives you gpm output at a given temp rise. The chart is very close. It's all there if you do your homework.

Another thing to contend with is the very small screen filter on the inlet water supply of the heater. It doesn't take much to block flow! I ended up having to put a 5 micron filter on my floor heat return temporarily to clean the antifreeze. This was another determining factor when replacing my pump stand heater. A clogged filter would starve a pump stand!

Do yourself a favor and consider a hybrid high efficient heater like the HTP I have. I couldn't be happier with the performance and how cheap it is to operate.

Fyi. I heat the hp soap and wax cycles. The best day I ever had with my 4 bay self serve used 3500 gallons of water. I never once ran out of hot water....that is with the 55 gal tank model.

 

[lighthousecarwash]

Well I'm finally starting to see the light. I think my solution is going to be 3 Navien tankless units with the built in circulation pump. I'll plumb in a short re circulation loop right up to the mixing tank and auto and this should be able to supply hot water within a few seconds. I can also program the pump to only start circulating at a certain time so it won't keep the pipe hot all night. Am I on the right track? Have to give credit to Chris at carwashboilers also. Great guy and a wealth of information.

Thanks
Lighthouse

 

[2Biz]

Do you know how many gpm of hot water (most possible) your equipment can use at a given time? With the navian 240, 199k condensing heater, you get about 5.1 gpm at 77deg. Temp rise. 3 of these heaters in parallel gives you little over 15 gpm heated water @ 70-80 temp rise. Is this going to be enough?

 

[lighthousecarwash]

Well I calculated 18 GPM if every single hot water function was running at the same time. I'm being told that will never happen. In fact they told me 2 would be enough but I want the third one to make sure. Do you think 4 is the minimum? Soap and wax are the only HP functions with hot water and the rest, including the autos, are all low pressure.

 

[wash4me]

You could install 2 and just have tees for the third so it's prepared just in case. I have often thought this would work 90% of the time. Put 2 floats in the tank. High float is from the tankless hot water unit and if the level gets below say 3/4 of the way down you have a second float that would be supplied from either cold water or a 50 gallon residential water heater. If you don't want to install a second float put in an electric float and solenoid valve. Personally I would try this with one tankless and you may be surprised how infrequently the second float would come on because you have the benefit of several gallons of storage in your holding tank.

 

[2Biz]

If you are considering installing 3 demand heaters, at minimum, I would install an additional low water level solenoid or float in case of a low water situation lIke wash4me suggested. I've learned to never say never owning a cw. If it can happen, it will happen!

I can think of many reasons why going the htp or similar route is the better choice. Have you considered it? If you have, whats your reasoning with the decision you've made? Just curious?

 

[lighthousecarwash]

My biggest issue is space. The equipment room is packed full and I will alleviate some of that with the new razor as it's pumping station is half the size. But removing that big boiler and 100 gallon holding tank will free up a lot of space that I'm going to need. I'm really leaning towards 4 of the Naviens and plumbing in a recirculation loop. I have tossed around the idea of keeping the holding tank and just going to tankless for the energy savings, but there are drawbacks to that route also. Keeping my current holding tank would certainly be cheaper as I could probably get away with 2 or 3 tankless units since the holding tank would act as such a large buffer.

Thanks,
Lighthouse

 

[Mr. Clean]

I have three Navien 240s that adequately provide

 

[Mr. Clean]

I have three Navien 240s that adequately provides 120-125 degree water to six bays using a 125 gal storage tank. They handle the busiest days w/o a problem.

 

[lighthousecarwash]

How many bays are you running, at what temp, and are you using any holding tanks?

 

[washnvac]

At one of my locations, I use a single 199,000btu Rinnai with a boiler coil on a closed loop with an open 30 gallon storage tank to supply 9 self serve bays. Rinnai set at 160. Holding tank set to maintain 120. No issues. This was previously done by a 700,000btu propane heater. Monthly savings is about $400--quick payback.

At two other locations, using a single 199,000btu Rinnai to direct feed 10 gallon holding tank for 5 s/s bays and pre-soak for one automatic. I have a low level water feed on the holding tank, in case water runs low you get another cold feed in. Rinnai can only supply 8.5 gallons at set temp. Experience has shown normally only 2 bays running hot at the same time (hp soap or hp wax) for 6 gpm. A third bay would run holding tank down by 0.5 gpm until someone switches functions; or the low level feed would maintain water in tank. Yes- possible the water drops below 120 for a short period; but very infrequent.

I have been extremely happy with these set ups.

 

[wash4me]

I'd be curious to know if you just had two if that would keep up.

 

[wash4me]

Washnvac what is a boiler coil?

 

[washnvac]

Boiler coil--I may not have used the exact term. But it is a spiral, finned copper tubed thingy. It sits in the open tank. A grundfos circulator runs water through it up to the Rinnai. (closed loop). Rinnai heats coil, which in turn heats water. Tank is filled with cold water from a float. I had to do it that way at that location because it is 9 bays. This saved me money, because I do not need multiple heaters now.

It defeats a little of the "on demand" concept, because I am keeping some water in a holding tank. But otherwise I may have need another heater or two. What I do know, is I am saving $300-400 per month over the old propane boiler.

 

[2Biz]

The key to saving money is going from the old dinosaur 70% or less efficient boilers to the newer condensing/modulating heaters and getting the most out of the fuel used. Whether tank style or on demand. I think my old 350k btu Jarco was about 30% efficient because the coil fins had disentigrated from condensation. So going from that to something 96% efficient is bound to save you money! Lots of $$$.....

I like the idea of the heat exchanger method...basically the same thing as the htp and possibly a little cheaper. I'm still concerned about feeding a float tank with water direct from the demand heater. It also seems like a lot of plumbing/venting if you have to have multiple units. The htp was a much easier install, I'm sure.

 

[Sequoia]

+1 to 2Biz about slaying the dinosaur boiler. My 350k btu Jarco would heat the equipment room to 80 degrees in the dead of winter since there was so much loss. When I installed a Knight boiler (from Chris at carwashboilers) one of the first things I noticed was how COLD the equipment room was in winter. Due to the boiler efficiency of course.

The Jarco had two settings-- full blast versus OFF. The Knight boiler (floor heat) starts at 100% burn rate, but as the water from the return slab starts warming up it modulates down from 100%. Once the slab is heated, my 150k knight boiler happily hums along at 20%, or 30k btus. So, I'm achieving the same thing while only using 10% of the propane from before. +1 on working with Chris at carwashboilers.

When I researched on-demand heaters a few years ago, I found one brand that was different from the rest. If it couldn't keep up with the demand placed on it, it kept the flow up but simply didn't get the water as hot as was desired. All the rest reduced flow, which potentially causes pump problems downstream.

 

[2Biz]

When I researched on-demand heaters a few years ago, I found one brand that was different from the rest. If it couldn't keep up with the demand placed on it, it kept the flow up but simply didn't get the water as hot as was desired. All the rest reduced flow, which potentially causes pump problems downstream.

I know Randy has the "Junkers" brand demand heaters that are this way. Full flow - no restriction. He has one for each bay. What heater did you find that was unrestricted? I never found one like that...I think I researched them all!

 

[Sequoia]

Well, I belatedly found an answer to this question. I was in my trusty plumbing supply house today and the rep told me that Noritz tankless water heaters will maintain full flow and sacrifice temperature if the demand it too great to keep the temperature up.