Thread: Tankless water heaters

I am seeing more and more tankless water heaters now. Have you had any experience with poor water pressure because of tankless water heaters?

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Thats what they do... They will keep the same temp but will slow way down if over task. I've been thinking about installing small ones in the kitchen and bathrooms.

Best

Ron

Originally Posted by mathew stouffer

I am seeing more and more tankless water heaters now. Have you had any experience with poor water pressure because of tankless water heaters?

MS: Water pressure is determined by the pressure supplied by the water utility, and the sizing of the piping in the house, not by water heaters, tankless or otherwise. Now, if you are discussing water flow, that is another thing which is determined by the fixtures installed.

Tankless heaters do have a pressure loss some more than others. They also restrict the flow to ensure it is delivering the set water temperature. I can not wait till they rewrite the code to say that a tankless water heater must be sized properly to supply hot water to all the fixtures that are turned on.

From Noritz Spec sheets I have show that when the flow rate is around 4.6 GPM on there 842 model and the temperature is set at 120º or less there is a 5 PSI loss and if the flow rate increases to 8 GPM the Pressure loss is 15 PSI All tankless heaters have a pressure loss chart so a plumber can properly size the heater to the home or building.

I get many people wanting to put in the smallest tankless unit here in the Chicago area cause they advertise that it will deliver 5.2 GPM @ 45º Temp rise. What people fail to realize is our incoming water is around 50º and needs a 70º temp rise to reach 120º which for the smalls heater that will only delver 1.7 GPM If they have one bath a washer and a kitchen sink they could get away with a unit that promises 7.5 GPM @ a 45º rise, but if you add two or three bath rooms you will need to go to the 9.2 GPM unit or run multiple units to provide enough hot water when all the fixtures are being used.

They will argue with me that its only him and his wife there they do not need it plumbed in to handle all the fixtures at once. There are guys on the DIY forums that will argue the same point. But what happens when a Family of 6 move into a 3 bathroom home and 3 of the 6 people all need to shower at the same time and be out the door at the same time?

Most manufactures will tell you "SIZE THE HEATER TO THE HOME, NOT HOW MANY LIVE THERE" OK I am sorry about my little rant here. But I see to many contractors that more than willing install a wrong sized heater per the home owners request just to make a buck.

I would have to say I lose 9 out of 10 calls because I size the heater to the home. And if they question the model I picked I will try to educate them, and the ones that realize what I am saying is correct way to do things are the ones that hire me to install a tankless system that will make them happy for years to come.

What people fail to realize is our incoming water is around 50º and needs a 70º temp rise to reach 120º which for the smalls heater that will only delver 1.7 GPM

That was one of the reasons I decided not to install one. Our water gets pretty cold in the winter time, and to get the performance we needed, it started to get pretty expensive.

RH: I often see new construction where a 4-bedroom house is serviced by a single 50-gallon water heater. The builders here flaunt the fact that there is no agency to enforce manufacturers' instructions, unless of course you (stupidly) look to the municipal AHJs for that. The same is true of tankless units or any other mechanical equipment. If it is not properly sized and installed the end results are not splendid.

Originally Posted by Ron Hasil

Tankless heaters do have a pressure loss some more than others. They also restrict the flow to ensure it is delivering the set water temperature. I can not wait till they rewrite the code to say that a tankless water heater must be sized properly to supply hot water to all the fixtures that are turned on.

From Noritz Spec sheets I have show that when the flow rate is around 4.6 GPM on there 842 model and the temperature is set at 120º or less there is a 5 PSI loss and if the flow rate increases to 8 GPM the Pressure loss is 15 PSI All tankless heaters have a pressure loss chart so a plumber can properly size the heater to the home or building.

I get many people wanting to put in the smallest tankless unit here in the Chicago area cause they advertise that it will deliver 5.2 GPM @ 45º Temp rise. What people fail to realize is our incoming water is around 50º and needs a 70º temp rise to reach 120º which for the smalls heater that will only delver 1.7 GPM If they have one bath a washer and a kitchen sink they could get away with a unit that promises 7.5 GPM @ a 45º rise, but if you add two or three bath rooms you will need to go to the 9.2 GPM unit or run multiple units to provide enough hot water when all the fixtures are being used.

They will argue with me that its only him and his wife there they do not need it plumbed in to handle all the fixtures at once. There are guys on the DIY forums that will argue the same point. But what happens when a Family of 6 move into a 3 bathroom home and 3 of the 6 people all need to shower at the same time and be out the door at the same time?

Most manufactures will tell you "SIZE THE HEATER TO THE HOME, NOT HOW MANY LIVE THERE" OK I am sorry about my little rant here. But I see to many contractors that more than willing install a wrong sized heater per the home owners request just to make a buck.

I would have to say I lose 9 out of 10 calls because I size the heater to the home. And if they question the model I picked I will try to educate them, and the ones that realize what I am saying is correct way to do things are the ones that hire me to install a tankless system that will make them happy for years to come.

Ron- good post, thanks!

Contractors, not unlike home inspectors, are generalist and expected to know everything about everything. We often rely on the subcontractor for their expertise, but unfortunately they are often less educated in their own trade than the contractor. This is why I love this site, I am always learning from those like yourself willing to share what you know.

Originally Posted by Ron Hasil

I get many people wanting to put in the smallest tankless unit...

Does someone have a link to a good tankless sizing info-sheet ?

Originally Posted by Joe Klampfer

Does someone have a link to a good tankless sizing info-sheet ?

JK:

http://www.hotwater.com/lit/im/res_gas/186965-001.pdf


Tankless Water Heater Buying Guide

Estimation Guide – What size tankless water heater do you need?

Estimation Guide – What size tankless water heater do you need?

Energy Savers: Sizing a Demand (Tankless or Instantaneous) Water Heater

Titan Tankless Water Heater Sizing Guide

Takagi USA - The tankless water heater pioneers. Experience "Endless Hot Water"

Originally Posted by Joe Klampfer

Does someone have a link to a good tankless sizing info-sheet ?

The thing is you need to know what your incoming water temperature is, and know what GPM the model you are looking at will deliver at the needed temperature rise. Every manufacture will have a chart that has Temp rise on one side and GPM delivered on the bottom.

Noritz has a nice one Hast temp rise on the side and model # on top


Once you know what your temperature rise need is you need to figure out what the max demand of the home or building can be at peak times. a Two and half bath home with dishwasher, and washing machine peak can be 10 GPM if both showers,the dishwasher or kitchen sink and the washing machine where all running at the same time on full hot. But since people do not shower at 120º F the more common setting for a shower is 110º to 115º (115º being what the shower temperature limiter should be set at for residential 110º for public showers)

We are mixing in cold water in the two showers, which will bring us down to around 7 GPM Most people also do not do laundry while they are taking showers so that can save us another 3 GPM So that would bring us down to a usage of around 4 GPM . Now lets use my incoming water temperature of 50º F so that means we want a 70º Temperature rise to get 120º output water temperature. If you look at the chat I posted above you will see 70º temperature rise with the model 751 will provide us with 4.8 GPM as long as they do not do wash while both showers are going, or if they are washing cloths and take only one shower this heater will do the job.

But lets say this family does run the water all the time both showers dishes, and laundry. That brings us back to around 7 GPM the only model that can provide over 7 GPM at a 70º temperature rise is the 1321. The 1321 model costs over 5K just for the heater, it is ASME rated due to its high BTU rating and is more of a Commercial heater. The way I would handle this is install two of the model 751's They have a simple data link to communicate with each other so when the demand is less then the 4.8 GPM a single heater can provide only one heater will fire, but once it reaches 80% capacity it will tell the other heater to fire up so with the both of them working together you will get 9.6 GPM also now you have redundancy. Redundancy means if for any reason one heater needs service the other heater will still be able to provide you with hot water.

I hope this helps you all a little bit. If you still have questions go ahead and ask away.

Originally Posted by A.D. Miller

MS: Water pressure is determined by the pressure supplied by the water utility, and the sizing of the piping in the house, not by water heaters, tankless or otherwise. Now, if you are discussing water flow, that is another thing which is determined by the fixtures installed.

Even here, the "experts" don't know the difference between pressure and flow rate. I deal with this miss-conception ALL the time with "civilians" during HI work and on line answering plumbing questions on AllExperts.com

If the system is undersized or miss-installed, it will choke off the flow rate. Any piping, fittings, or valving adds friction loss. I used to see this most often on water softeners. 1 inch pipe feeding it and the house but a 3/4 inch valve head. "I got no water pressure after they installed my new softener" Wonder why?

Thanks for the great information Ron H. Much obliged!

How about the hybrid tank/tankless water heaters? Do they address some of the concerns over flow rates?

Great information, thanks guys.

Originally Posted by Dan Cullen

Thanks for the great information Ron H. Much obliged!

How about the hybrid tank/tankless water heaters? Do they address some of the concerns over flow rates?

They Hybrid systems have the same flow rates as the tankless water heaters, but they have a tank to help with recirc systems. Other than that they are just overprice systems.

Other than that they are just overprice systems.

RH: That is what I thought and appreciate hearing it from a wrench-slinger.