What size tankless water heater needed for a 5 bay?

[csmith]

I'm looking into getting a new water heater, I've got an old boiler that currently is out. I'm wanting to get a tankless water heater that mounts on the wall, I've got five bays and I'm wondering what size will easily keep up with my needs at my wash any tips or ideas appreciated!!!

 

[mjwalsh]

csmith,

Your inlet water temperature coming in will be a major factor when it comes to sizing. Having two tankless set up in a modular step fired way may also make sense.

mike www.kingkoin.com

 

[2Biz]

Even 2 set up in parallel may not be enough...Keep in mind most demand heaters in the 199k range restricts flow based on temps setting and input pressure. I have a 199K BTU high efficiency wall mounted demand that heats my floors...At 40psi and about 40° Delta, I only get 6.7gpm output... The heater is rated at 10gpm...To get 10gpm, you have to run 100psi inlet pressure according to the flow charts...Which I wouldn't do! So given that...You may need 3 demand heaters...A typical bay at 1200 psi and a 2506 nozzle uses appr. 3 gpm...

You might want to consider a Natural Gas HTP or equivalent High Efficiency tank style instead...You won't be disappointed!

 

[Randy]

I have one on demand water heater per bay, my bays are fed with reduced city water pressure, and I don’t have a gravity fed tank.

 

[I.B. Washincars]

Is it that big of a deal if a water heater is a bit undersized when used for SS only. As long as you have flow on busy days, can the customer really tell if the water is 90 degrees, and not 110-120? As long as the hose is not ice cold in their hand, I think it's much ado about nothing...JMO

 

[2Biz]

IB, It has more to do with starving a pump...If you only have 1 demand heater for 5 bays and it only puts out 6-7 gpm with no more storage than a float tank, you'll run out of water in the float tank which will starve and cavitate the pumps...

Most demand heaters are not flow through like my HTP...Demand heaters restrict flow to achieve a set temp output...It could care less about demand...

 

[I.B. Washincars]

Demand heaters restrict flow to achieve a set temp output...It could care less about demand...

That would be a deal breaker for me. Demand is much more important than the temperature. I can't see much benefit in that type of heater with a big negative like starving the wash looming.

 

[2Biz]

Bingo! That's why after researching and having one on my floor heat, I went with the HTP with 1" NPT pass through for the bays. Even if you run out of hot water, (highly unlikely though), water flow and pressure are not restricted in any way. You just get cold water. My busiest day used 4400 gallons of water...I never ran out of hot water!

 

[loewem]

To reinforce what 2Biz is saying, I have a 199k btu on demand water heater. I have the problem of running out of hot water on busy days and have had to add water only hydrominders (cold city water) on my rinse tank and on my automatic soap tank (both draw hot water). Pretty awful feeling to be having a great day and then hear the building shaking because every pump is cavitating or to watch the automatic spray arch go around a car without spraying a drop of chemical. Might be worse to think about the strain on the equipment. 2Biz clarified my problem for me. If he can explain in a way that makes sense to me then he definitely knows what he is talking about. I've started looking into the HTP or comparable water heaters. As 2Biz said, the flow through on the HTP is the important part. When my on demand heater hits the wall it generates almost nothing in the rinse tank and absolutely nothing in the soap tank.

 

[wash4me]

You simply feed the on demand to the main tank valve and add a second float to a solenoid valve that is low in the tank. This second float valve can be fed by just cold water (or hot if it's available) and that will keep tank from emptying but give you warm water instead of hot in the busiest of times.
an additional thought I think just plain old commercial gas water heaters are fine and simple. 199000 btu will easily do 5 bays with a plain old commercial natural gas water heater.

 

[2Biz]

I guess what I have is just a plain old commercial gas water heater! It just happens to be a high efficient, modulating, condensing one that sips the NG! You get what you pay for. I've already saved the cost of the heater in fuel bills, allows me to stay more competitive on bay price compared to the other washes in town, and have gained 15% in income each year after installation...People do notice!

 

[wash4me]

I am just not familiar with Natural Gas HTP. Most of the massive expenses people incur on natural gas bills are the old oversized boiler with separate storage tank units. On your HTP unit at what water temperature does it stop condensing?

 

[2Biz]

I have mine set at 100°. I've never seen or felt the PVC vent get even slightly warm...It has 5 stages of modulation up to 199k btu. Lowest is about 25K btu. I hardly ever hear it ramp up to a higher setting than the lowest. Here is a link to the heater I have. Its 55 gallons and produces 300-400 gph at 100°....

http://bostonheatingsupply.com/phoenixph199-55.aspx

Mine doesn't look quite like the one listed...Mine looks like this...

 

[wash4me]

Looks like a nice unit. That's about what the triangle tube 250 condensing boiler cost me but it requires heat exchangers, pumps etc. in addition.

 

[Rudy]

Did you install the HTP yourself? If so, do they honor the warranty?

 

[2Biz]

I installed it myself. Never had an issue with it, so never tested the waters!. We have an 80 gallon Aosmith at work that is similar. It's over 20 years old and never an issue.

 

[Rudy]

You've got me thinking now. I see the HTP has two sets of "inputs/outputs" for water. Is that correct?

My Raypak is 23 years old....and my wash also was built with a dedicated residential hot water heater (40 gal)used to supply heat for a glycol loop for the hose trough on the roof....as well as heating my two automatic touchless trolley rails (racetrack shape).

I wonder why I couldn't upgrade...and eliminate TWO heaters. I'd plumb a brass heat plate exchanger to supply the "rail/trough" heat....and plumb it into the second set of connections on the Phoenix. One connection for Self Serve hot water...the other for feeding a heat exchanger for hose/automatic deicing???

Also...

Any guess on the present efficiency of a 20+ year old Raypak? I think they were 80% when new.

 

[2Biz]

Yes the two inlet and outlet fittings on the right side of the tank are to attach a circulator and heat exchanger...As you stated, you have to use a heat exchanger since those two fittings just go to the tank...There is no internal heat exchanger on those fittings. I put ball valves on just in case I ever needed them for something...SO yea, I can see the HTP handling a lot more than I throw at it! Plus it has a SS tank and 2" of insulation that boasts a 1° temp loss in 24 hrs....Not a biggy, but this thing is really efficient! Every little bit helps. I did plenty of research when looking for a bay water heater...Demand, boiler, and tank style...The HTP was by far the best I could find with 1" NTP fittings and efficiencies/construction....I believe 1" at 40 psi flows 40 gpm? That's a lot!

My Old Jarco WEBN boilers were 70% efficient when new. Since the PO's ran them in a condensing state, the internal coils self destructed from acidic condensate. There wasn't any fins left on the copper tubing when I tore them apart for scrap...I bet the Jarcos were down around 25% efficient at that point! Actually I couldn't afford to run them...

I also plumbed in a cold water bypass to my hot water float tank thinking I would switch to cold water in the summer. It turned out to be so cheap to operate I just let it run year round...Customers love it and comment on it all the time that I'm the only CW for miles that has heated water...Again, it DOES make a difference, even if only from perception!