TankLess Water Heater for Heating

nycpa

Has anyone come across a two zone tank less water heater that can double up as hot water heating for baseboards? One zone used for hot water and second for hot water heating? Does this work, does it cause problems? This would in affect replace a tanked hot water heater and hot water boiler. Thanks

Snowmelt

Yep it's a navien combo unit

Ironman

Several other manufacturers have them as well.

One thing to watch out for, and this applies to any of them: the on board pump only moves about 4-5 gpm through the boiler and no matter what they claim in their advertising, that translates to 40 - 50k btu's available for space heating if you have high temp emitters designed for a 20* delta T. It doesn't matter that the input is much higher, that's all that the pump can deliver because it's designed primarily for the domestic side. If you have medium or low temp emitters, then you'll be able to get more capacity to the space heating side. Btu's = (gpm x 500) x delta T.

Rich_49

This is what you're looking for . Bob , check this one out , actually installable from my standpoint . watch the video and check out the differences .
http://www.htproducts.com/EFT_Combination_Floor.html

JohnNY

They're called "combi units" and there's a bunch of them out there.

HDE_2

Ironman said:

Several other manufacturers have them as well.

One thing to watch out for, and this applies to any of them: the on board pump only moves about 4-5 gpm through the boiler and no matter what they claim in their advertising, that translates to 40 - 50k btu's available for space heating if you have high temp emitters designed for a 20* delta T. It doesn't matter that the input is much higher, that's all that the pump can deliver because it's designed primarily for the domestic side. If you have medium or low temp emitters, then you'll be able to get more capacity to the space heating side. Btu's = (gpm x 500) x delta T.

Your reference to the universal heating formula for heat emitter output rarely applies to boiler operation and output.

If that was the case I could take a standard cast iron 100,000 BTU boiler with a 10 GPM circulator and adjust its H/W 20 degree DT control to 30 degrees and make it a 150,000 BTU boiler right?

What about I adjust it to a 10 degree DT? its now only a 50,000 BTU boiler? Not, it fires still at 100,000 and cycles a bit more. In fact if set at 180 degrees with a 10 DT, 175 degree average water temp puts out more heat than the average of 160 & 180 (20 DT) which is 170 degrees.
Cycles often yes but warmer water to emitter at same flow rate equals more heat output.

The universal formula is not about boiler outputs, that's defined by specific manufacture burner operation.

Ironman

"Your reference to the universal heating formula for heat emitter output rarely applies to boiler operation and output."

"If that was the case I could take a standard cast iron 100,000 BTU boiler with a 10 GPM circulator and adjust its H/W 20 degree DT control to 30 degrees and make it a 150,000 BTU boiler right?"

"What about I adjust it to a 10 degree DT? its now only a 50,000 BTU boiler? Not, it fires still at 100,000 and cycles a bit more. In fact if set at 180 degrees with a 10 DT, 175 degree average water temp puts out more heat than the average of 160 & 180 (20 DT) which is 170 degrees."
"Cycles often yes but warmer water to emitter at same flow rate equals more heat output."

"The universal formula is not about boiler outputs, that's defined by specific manufacture burner operation."



You really don't get this do you? I never said that it was about boiler output. Quite to the contrary, I have stated repeatedly that it's not the input/output of the the boiler but the ability of the circulator to move enough gpm to get the necessary btu's to the emitters.

"If that was the case I could take a standard cast iron 100,000 BTU boiler with a 10 GPM circulator and adjust its H/W 20 degree DT control to 30 degrees and make it a 150,000 BTU boiler right?"


That statement is ludicrous and clearly shows that you refuse to open your mind to what I've been saying. The circulator has NOTHING to do with BOILER output. But it has everything to do with EMITTER output. The circulator is like the engine on a train that carries the load to its destination. The boiler is the source. The emitters are the destination. The circulator and piping are the train that carry the btu's. If the train is too small, it doesn't matter how large the source or the destination is; it can only carry a limited amount at a time.

It appears that you have the misconception that because the circulator is located in the boiler cabinet, that it becomes part of the boiler's output rating. Whether in or out of the cabinet, it doesn't change things. The output of the boiler is the ability of the burner and the heat exchanger to produce heat measured in btu's. The circ has nothing to do with that rating. Again, it has EVER THING to do with how many of those btu's get to the emitters.

You appear to be an intelligent man. Why is this so hard for you to grasp?

HDE_2

"The output of the boiler is the ability of the burner and the heat exchanger to produce heat measured in btu's. The circ has nothing to do with that rating. Again, it has EVER THING to do with how many of those btu's get to the emitters".

That's not what you were stating here, so bear with me on your confusing message:

" the on board pump only moves about 4-5 gpm through the boiler and no matter what they claim in their advertising, that translates to 40 - 50k btu's available for space heating if you have high temp emitters designed for a 20* delta T. It doesn't matter that the input is much higher, that's all that the pump can deliver because it's designed primarily for the domestic side."


So to be clear are you stating the BTU's are limited to 50,000 when you attempt to use the boiler pump as the heating system circulator also? If you are I understand your message.

But being that many but not all boilers don't allow this and require a primary pump to move the heat through the system from the boiler secondary injection flow your first statement earlier is confusing and partially wrong

Which one did you mean?

Ironman

Neither one is confusing or wrong. Again, it doesn't matter whether it's inside or outside of the cabinet; whether it's a primary or secondary or boiler circ, or whatever name you give it. It's still a circulator that has nothing to do with the output rating of the boiler, but has everything to due with how many btu's reach the emitters.
I could understand a home owner being confused because the circ comes on board with the boiler, but not someone in the industry that knows the circ has nothing to do with the output rating.

HDE_2

Ironman said:

Neither one is confusing or wrong. Again, it doesn't matter whether it's inside or outside of the cabinet; whether it's a primary or secondary or boiler circ, or whatever name you give it. It's still a circulator that has nothing to do with the output rating of the boiler, but has everything to due with how many btu's reach the emitters.
I could understand a home owner being confused because the circ comes on board with the boiler, but not someone in the industry that knows the circ has nothing to do with the output rating.

I am not understanding this explanation after you have also stated:

"the on board pump only moves about 4-5 gpm through the boiler and no matter what they claim in their advertising, that translates to 40 - 50k btu's available for space heating if you have high temp emitters designed for a 20* delta T."


If anyone else reading this is confused as I with which message Bob means to convey, or has a better understanding please share.

For now, I suggest anyone questioning the true output of a boiler to reference the AHRI directory that verifies third party testing. I looked and noticed the NCB-240 listed as 120,000 heating input, 112,000 heating capacity, 97,000 Net AHRI Rating (formally IBR). That's a far cry from ":40-50K BTU's".

Surely you don't feel AHRI is deceitful?

Gordy

This appears to be an old thread brought back to life.

HDE,

I have no problem comprehending Ironman's statement it is quite true.

Allow me to put forth another analogy.

We have a rock crusher in a quarry crushing 10 tons a minute it's the boiler. The rocks brought over to the crusher is the fuel to burn, and the crusher is the heat exchanger, and the crushed stone is the btus made usable.

We have a conveyer belt designed to carry 10 tons of the crushed rock a minute this is the piping. Again the crushed rock is usable btus.

We have a motor (pump) driving the conveyer belt (piping). The motor which is to small for the max delivery of the conveyer belt system. It was a design flaw to the conveyer system, and only allows the conveyer to put out half of its max capacity of 10 tons per minute.

At the end of the conveyer we have trucks (emitters) hauling the rock away as it comes off the conveyer belt able to meet 10 tons minute design capacity. Since the conveyer only puts out 5 tons a minute because the motor is to small we have rocks over flowing at the crusher ( btus up the flue), and trucks only hauling half loads, and a rock pile slow to form ( btus emitted).

It does not matter where the motor was installed to drive the conveyer it still only drives it so fast.

Ironman

HDE said:

":40-50K BTU's".

Surely you don't feel AHRI is deceitful?

No, I don't feel the AHRI is deceitful, but I definitely feel that Navien's advertising is. And you are obviously confused about the fundamentals of hydronics.

The 120k output is just that: the output available from the heat exchanger. It does NOT mean that you can get that many btu's to the emitters with the on board circ. You could if the emitters were low temp and you had a 77* delta T between them and the boiler because that's what that circ is sized for: a 77* delta T. That's what you have on the domestic side and that's what the circ is sized to. Connect it to a high temp system designed at a 20* delta T and your gonna get 45-50k btu's. It's simple math that's proven beyond dispute.

Navien knows this. I've challenged their trainers on it and they sheepishly admitted it when pressed. But they also know that home owners, plumbers and most people in the HVAC trade DON'T know this and will buy and install the boiler THINKING that their getting 120k btu's going to their baseboards only to find out down the road that they're not. THAT, sir, is deceitful!

The limited ability of the the circ to deliver the full btu rating with high temp emitters is not limited to Navien; all the combi's that are designed like this have the same issue. The difference is that some are honest enough to admit it.

I suggest you read Bosch's application manual for the Green Star combi as see how they are honest enough to state it there.

HDE_2

You say you don't think AHRI is deceitful yet you accuse Navien of false advertising after their ratings are tested and audited by AHRI. The DOE test standard for boilers is 180 degrees, 20 DT. If that's followed and testing by 3rd party and is audited by AHRI as a requirement of listing, the facts stand.

So that would be a direct accusation in my book.

Its not uncommon for persons including trade professionals to confuse Gil Carlson's universal heating formula for BTU delivery in a system, to BTU operation of a boiler. Note go back and read all you can locate on the subject, as it always refers to system BTU delivery, not the boiler operation.

So unless we both have the operation data of the boiler and burner operation, neither of us know how the boiler actually works. And as you mention, perhaps a Navien trainer didn't know either.

If you're familiar with the mixed stream formula, it may take a higher boiler supply water temperature if the boiler flow is lesser than the system flow to hit desired system water temperature, but that doesn't limit the boiler output. As return water temps rise due to emitter saturation or reduced flow at zone(s), the supply temp will also increase to meet supply set water temp.

BTW: I am far from confused, my knowledge is far beyond that of a heating contractor.

Jack

"BTW: I am far from confused, my knowledge is far beyond that of a heating contractor."

Yikes! You do know who you are talking to here don't you? Remember, be nice. Be respectful!

This reminds me of the scene in the Wizard of Oz where Dorothy and crew are cowering before the wizard and the curtain blows back. "Pay no attention to that man behind the curtain...., I am the Great and Powerful Oz"

Zman

"BTW: I am far from confused, my knowledge is far beyond that of a heating contractor."
Wow!
I agree, your problem is not that you are confused....

Harvey Ramer

HDE,
We are all perfectly aware of the boiler's output when piped primary secondary to a system operating on a lower design temperature. In that scenario the on board pump only needs to move a minimal amount of water and the Delta -T between the supply and return will be high, hence the high BTU output.

Now put yourself in the shoes of the unsuspecting contractor. He has to put a new boiler in a 4,000sf house that has hot water baseboard. The house only has enough linear feet of baseboard to meet design load with 180°F water. (Drop the water temp and the baseboard won't meet design BTU output.) The heat load on the house is 150,000 BTU. He puts in the largest Navien combi because the rep told him it has a BTU output of 170,000.

Now, you know damn well that the Navien won't meet the load in the above scenario. Do you think the contractor should have known the BTU output was dependent on a lower than normal system water temp. I think he should have, but than again, if he went to a training class and wasn't made aware of this fact? Who's fault is it now?

The scenario I described is not so uncommon! In many high temp Navien installs, the only saving grace is oversized radiation that allows the system to meet load at a lower average water temp when piped p/s.

I should think a boiler manufacturer would have the desire to be quite candid with their product and make every effort to see that it is used properly and for the right application.
Don't you feel the same way, HDE???

icesailor

Which is why so many "Not Know That Much" installers get away with installing wall mounted beer cooler boilers. In old houses, the resistance has been upgraded and they work fine on 170 degree or less water. When the original emitters were designed for 180 degree or higher water temperatures, or just plain oversized in the first place.

HDE_2

Harvey
I can certainly understand how that can happen. However If the contractor was to look past the total BTU's available for the domestic side being that the product is a combi and pay more attention to the published ratings on the heating then he wouldn't be in a pickle of being undersized right?
That's his fault all training aside.

Jack struck a chord with you I guess, not my intention. Your reading it wrong, the intention was to state more of my education and industry passion than anything else.

Looking at the Navien NCB manual, they have a lot of features to overcome many of the potential issues mentioned here. To name two, boost and adjustible overshoot. Operationally or time wise the boiler supply temp can raise above that 180 set point to give the extra temp to meet the marginally sized baseboard.

Any Navien experts on here even aware of this?

Steamhead

This is turning into the PVC venting thread- deja vu all over again.

http://forum.heatinghelp.com/discussion/151352/pvc-venting-on-boilers-again#latest

HDE_2

What can I say. Nowhere have I ever posted opinions or hearsay like others. Only the facts.

QWSmonster

Why not install a new boiler with an indirect water heater? I've found combi units to have reliability issues in CO.

Ironman

HDE said:

BTW: I am far from confused, my knowledge is far beyond that of a heating contractor.

HDE said:

What can I say. Nowhere have I ever posted opinions or hearsay like others. Only the facts.

Wow, we lowly mortals are so blessed to have you here.

rrwitherspoon

Wrong person