Knight vs. Vitodens

rumn8r

Paul,
While I could use just one Vitogas or Vitola because they are available in higher capacities, I think that I prefer to have two smaller units for redundancy. Because the price of all 3 are ± 15%, there would be little difference in price if I went with 2 units. However, 2 Knight boilers would cost less than one Vitola. Even if supply temp exceeds that required for condensing on the coldest days, it should be condensing most of the time.

Joe Brix

Knight vs. Vitodens

Anyone have experience with both that can help me through the comparisons? My application will require 2 units (~250 k btu/h total) plus multi unit controls and outside temp compensation. Heat consumers include hydro air coils (3), indirect HW (60 gallons), and pool HX (135 k btu/h). I know that both have SS heat exchangers and that allowable vent length is much greater for the Knight which is why I am interested in it. I also know that the Knight has only been in production for a year or and assume that the Vitodens has been in production much longer. I also know that the Knight is available with greater capacity and I could use just one unit but I choose not to for redundancy. I am not looking to start an altercation here; just looking for what I should consider for my application.

Robert O'Brien

It's

really not fair to compare Vitodens to any other boiler,they really are in a class by themselves.If you want the finest,go Vitodens.The materials and engineering are second to none. I've never installed a Knight but have serviced a few and they are nice,not a thing wrong with them. Just not a Vitodens. You get what you pay for.

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Joe Brix

That's what I hear...

but I need to know why. So, why?

Mike T., Swampeast MO

The burner and HX in the Vitodens have much to do with what sets it apart from all other boilers. While other boilers rely almost solely on flue gasses to exchange heat, the Vitodens has instantly transferred a significant portion of its output to the HX via radiation. The burner doesn't even produce "flame" in the conventional sense...

While many other mod-cons (including the Knight) use both primary and secondary heat exchangers, the Vitodens has only one. While other mod-cons may need insulation somewhere inside the boiler, the Vitodens has none because there is no need.

While some other mod-cons actually "modulate" via a series of set stages, the Vitodens can operate at any output level in its range.

Other mod-cons generally require combustion analysis and field adjustment of the air-fuel mix to both optimize performance and minimize "bad" emissions [presumably this is MUCH to do with the venting as installed in each job]. Combustion analysis of the Vitodens is only for verification with air-fuel mix that automatically and continually compensates for the venting to include adjustment for wind, atmospheric pressure and even icing.

The Vitodens is the only mod-con that does not have thermostat connections and normally has no form of indoor temperature sensor connected to the boiler itself. [I believe] is the only mod-con capable of accurately matching output to load in real time. With some non-too-difficult adjustment of the heating curve, the Vitodens is capable of maintaining indoor temperature very closely to the "sun dial" setting in any weather--this with no direct form of indoor temperature feedback (only outdoor temperature input).

Even Hot Rod was extremely impressed by the quality of construction and materials--that alone speaks volumes if you've seen the things he makes...

brucewo1b

Mike T, Brad White Anyone Else

Please help me out here, how can a heating plant control indoor temp with no t-stat or no form of indoor temperature sensor connected to the boiler itself. I understand no t-stat but when every house has a diferent infitration rate someting has to say the wind is blowing 50MPH from the north or 10MPH from the south or its dead calm out today.

marc friedman

don't listen to the Viessman brainwashing
you can buy a boiler for half thier price

to do the same job

Joe Brix

Does any of this translate to greater efficiency for the Vitodens compared to the Knight if they were in identical houses? If so, how?

Mike T., Swampeast MO

Infiltration is actually the easiest for the boiler to compensate. I'll get back to this later...

If you momentarily forget about wind, sun, occupancy gains, etc., you'll find that heat loss from a structure where room temp setpoint is exactly maintained is linear. It takes the same number of BTUs to compensate for the increased loss between 16° and 15° outside temp as it does between 35° and 34°.

This is the basis of the Vitodens control philosophy the goal of which is to establish a "target supply" temp that is just adequate for the individual structure using its individual heat transfer mechanism regardless of outdoor temperature. Given the linear nature of "ideal" heat loss, this is relatively easy and takes nothing more than a simple linear equation, e.g. the heating curve with slope and shift.

Where such does however become more difficult is ensuring that the boiler is actually providing the required number of BTUs to the emitters.

Such is the whole purpose of my recent series of posts regarding primary/secondary with mod-cons. I will again assert that it is impossible for a mod-con using any form of primary/secondary piping to match its output to actual loss unless primary (boiler) flow is variable.

This concept of continually matching boiler output to system load puts the Vitodens into a field of one. To my knowledge, no other boiler is capable (when using any form of primary-secondary).

To understand why the Vitodens is different, you MUST understand this concept!

Back to infiltration:

By definition, infiltration during the heating season is cold air infiltration. What happens when cold air hits any emitter? It tries to produce more output because the differential temperature has increased. If your boiler is striving to maintain a supply temperature to the emitters it will require more boiler output because the emitter is giving off more energy even though the supply temperature has not changed!

As I said at the beginning, infiltration is the easy thing. What's HARD is solar gain. Why? Because solar is RADIATION! It turns your windows into radiators which in turn warms OBJECTS which eventually warm the air. It also decreases the rate of heat transfer via the exterior walls since the outside surface of those walls at least acts as though it's warmer than the air surrounding. Warm air rises and most emitters (being close to if not the floor) don't see the increased gain for a significant period of time and do not decrease their output similar to the way they increase it with cold air infiltration.

Mike T., Swampeast MO

Most certainly, but how much depends upon your emitters and method of control.

In the system you have proposed however I still seriously wonder if any mod-con will prove to be the better choice over a well-designed system using conventional cast iron boiler(s). You need an EXCEPTIONAL heating contractor!

Brad White_150

Mike T. and I talked about that today on the phone, Bruce

The closest we got to was, "damned if I know".

:^)>

My setup (for my Susan's house) and Mike's house are similar: TRV's on the radiators, an outside sensor and no indoor feedback. The essential difference is that Mike's Vitodens is directly connected to his emitters; our flow goes through a Low Loss Header.


Weather has been similar in our locales, high 50's today and around freezing overnight last few nights.

The house holds dead-nuts at 68 degrees when the curve is set so. Granted, the TRV's do some of this but some rooms currently do not have the heads installed, that is in progress.

My thought was that the boiler must sense return water temperature (much as the Munchkin does). Mike says that there is no HWR sensor, just HWS... That the Vitodens has a known volume of water and known internal flow rate...perhaps from that there is an internal calculation. Oblique to say the least.

I have to go on the "HWR sensor" somewhere in there until proven that such does not exist. With a known/experienced flow rate and temperature rate change pattern, the boiler could figure heat loss. It is as if it seeks the output from the structure and meets it.

One comment I had as part of the discussion is that when a Vitodens is installed in a given structure, it essentially can tell you, indirectly, what the actual heat loss is. No other way to explain that.

Going in on initial setup, the curve is just a guess, limited by the accuracy of my calculated heat loss, my radiation EDR and assumed HWS temperature needed on a design day. The Vitodens "learns" and adjusts firing rate as you note, without apparent indoor temperature influence. If it has no HWR reference, I have no idea how it works at this point. But I sure am curious....

But the darned thing works.

Cosmo_3

your application

Mike is right on with describing the Vitodens.

In your application, with 3 hydro-coils, a DHW, and a pool heater I think that the Knight is a great choice. The Vitodens philosophy lends to the greatest ROI when used with radiant panel, or radiators. Design the heat emitters with constant circ, and let the Vitodens "Fly" on outside reset. A little tweaking of the heating curve is necessary, as well as designing the controls to maximise use of the free solar heat.

As far as construction Mike is spot on, no MOD/CON out there right now has better construction in the places you need it than the Vitodens.

I dare to say that the Vitodens compared to other brands may need less repairs over it's life span than the others. Of course that assumes it is installed correctly. If a contractor is more familiar with the Knight than the Vitodens, and he is a good craftsman no brainer stick with him. A brand is only as good as the install.


Cosmo

rumn8r

Why is my system a problem for mod cons? From responses to my other posts, I learned that hydro air can work with modcons while condensing by using 4 row hydro coils to achieve a greater delta T and that the pool HX should thrive with a mod con in condensing mode once the temperature setpoint is achieved. I would have the pool HX plumbed and controlled with a different aquastat to increase temp from a setback firing one of the modcons full flame (same as indirect HW). Does this make sense? How exceptional does the heating contractor have to be to do this?

Perry_2

I have to agree in part with this

There is a ballancing act that should be considered.

You can indeed by other boilers - and advanced control systems (usally in addition to the boiler)that can work as well as the Vitodens.

There are two issues to consider.

1) The really good control systems that can be added to most boilers is not cheap; and the cheap ones do not have the nice features. But, I think a reasonable argument can be made that you do not have to spend the kind of money that a Vitodens cost to get something that works well enough that most people would not notice.


2) Durability of the boiler. Lets be honest here: No one has a mod/con that has lots of years of service to prove they are long term durable. So you need to look at the design and construction of the HX, and burner and figure out which is likely to be durable. The Vitodens is outstanding - and I expect the HX and burner to last a long long time. The Triangle is my second choice (but their smallest boiler is a lot larger). And I did not think much of the designs and materials of the others I looked at.

Since installing a boiler cost a pile of money - regardless of the boiler; would it not be prudent to go with something that was designed and built to last - versus other things that were designed to be low cost. You would not want to have to replace your boiler in 5-10 years again, or have to pay for lots of service calls?

While perhaps not the best comparison on boilers - but something that does raise questions: If you look at the same sized Munchkin as the Vitodens 6-24 you will notice that it weighs 53 Lb in its shipping crate. The Vitodens weighs 143 Lb unpacked (not including a separate power supply). Now the Vitodens includes a pump (maybe 10 Lb) - but that leaves 80 Lb of other differences. I have heard people say that the Vitodens has a "heavy" steel cover. I think the cover is fairly light (and I have taken it off and put in on a number of times). So I scratch my head and wonder where the weight differences are - and how that affects long term reliability.

Best of luck in your search.

Perry

hr

If the choice is

two Knights or one Vito, for the same money...

With dual mod cons you get redundancy, step, stage, alternating firing and a 8 to 1 turndown ratio. For little to no extra cost with the Knights.

Viessmann may very well be the best, but it doesn't have that many tricks up it's sleeve

I don't see many places where mod cons don't make the most sense, your's included.

Old iron rad systems scare some due to the sludge and sediment potential. But this is not the mod con's fault. It may be wise to stick with iron for that type of install for the callback hassle factor. But it should not be a strike against mod cons. Perhaps a wide open mod con like the Prestige would be a better choice for questionable system sediment challanges.

hot rod

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joel_19

Hey Marc

Please, that was funny kinda like saying you shouldn't buy a BMW M5 cause a Chevy can do the same job for half or actually a quarter of the price . Then again why by the Chevy when you can have a Daewoo. Then again why buy the Daewoo when you could just get a used Pinto.

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Perry_2

Psst... Used Yugo for sale...

35,000 miles on it.

For the true tinkerer.

Any takers... (but you got to come and pick it up and haul it away).

Perry

Eddited to add: Just checked; he junked it - so its no longer availble

hr

It's probably the snob factor

more than anything that turns contractors away from V. I've looked long and hard at their offerings. Unquestionably the best build stuff I have seen.

Do we (you) need it? Maybe. I sure love my German car and past motorcycles, except for repair time

I've heard talk of a Volks-Vitoden for the less than "brightest" installer/ contractor.

That may interest me if superiority complex is left out

hot rod

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Bob Sweet

Bingo, not putting any words in hr's mouth BUT

the droolling all over ones self and the nose in the air attitude towards American manuf. completely tuns me off about the whole idea of the "BIG V".

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Mike T., Swampeast MO

I've looked over and over for any evidence of a return temp sensor in the Vitodens.

Nothing in the schematic. Nothing in the internal wiring into the combustion chamber. My last guess was that such might somehow be built into the internal circulator, but with only five wires (line, neutral, ground and two presumably for speed control) there just doesn't seem to be any way.

Neither is there any volume or differential pressure sensor for the water passing through the boiler.

The only way my little brain can make sense of this is that matching of boiler output to emitter load is assumed with the boiler "learning" how to vary output in just the right amount when the supply temperature attempts to change.

Joe Brix

Actually, it would be 2 Vitodens vs. 2 Knights. Going with Vitodens would require 2 units because of their relatively lower maximum heat output while Knights go up to ~500 k btu/h (I need 250 k btu/h total). I actually want 2 smaller units for redundancy. The price of 2 Vitodens is a bit less than twice the price of 2 Knights of the same heating capacity.

brucewo1b

OK here is what I find on line

Remote controls RS, with room
temperature feedback, and WS,
without room temperature feedback,
are available for connection to the
Vitodens 200.
Another remote control option is the
use of the Comfortrol programming
unit as a remote control. Simply
remove the programming unit from
the control base on the boiler, insert
a temperature indication unit in its
place, and mount the Comfortrol
programming unit on an inside wall
of your living area.
Operation of the heating system can
then take place right from your living
room or any other convenient
location.

So I take it that either there is one remote WS without room temp sensor but otherwise it is in the RS remote or the Comfortrol unit. So ae you saying that the way you two have it set up you have the WS remote with the Comfortrol in the basement??

Mike T., Swampeast MO

Aren't you also heating an indoor pool and dehumidifying the pool area that you really only want "up to temp" on weekends? This with the pool itself providing most of the heat for the room containing the pool when you want it but otherwise living off the energy in the [uncovered] pool when you don't?

While I don't know the size of the pool, you could well be talking about a MASSIVE influx of heat.

Brad White_150

Well, Bruce

The RS is the way we will go pretty soon, with the Comfortrol in the space as much for convenience as anything else, and with the temperature indicator in place on the boiler as code requires.

Right now the Comfortrol is in the boiler, in the basement. If it is sensing temperature in the basement, it would fire a lot more.

(Basement is partially insulated and runs about 8-10 degrees cooler than upstairs, with only the passive emission from piping yet to be insulated. A lot less of that now that it is 1" copper versus 2" iron.)

There is a dip or toggle switch so that the sensor (integral with the Comfortrol I am told) will participate when installed in the space.

The weather-responsive part does not change of course; it is essential to the curve. I can only imagine that indoor temperature sensing will fine tune the output, but given how it has been performing for the past three weeks, I have to wonder how it can be improved.

I certainly will report back!

Brad

Joe Brix

The pool is a 8,000 gallon lap pool and would require 67 k btu/h for a 1° F temperature rise (or twice that for 2° F rise per h). We would let the pool heat drop after the weekend and bring it back up on Friday. Pool temp would be set to 82° F when in use and not heated otherwise. Pool room temp would be 84°F when in use. The trick is that the air temp in the pool room must be 2°F over the pool to decrease evaporation which will cool and humidify the air. If we setback the air temp during the week, we will likely get evaporation because air temp will decrease more than pool temp and will likely require a control for that. I think the pool temp. would fluctuate less than 15° F, requiring 15 h to restore temp at 67 k btu/h. I would choose a larger HX (Triangle Tube MaxiFlo 135) to increase delta T so lower supply temps could be used.

brucewo1b

Well let me say Thank You to you both

I am just curious as to how it happens and I know that some people believe in black magic but sometimes it is just to far fetched for me to believe in, so if you do come up with an answer I for one would really appreciate it.

Mike T., Swampeast MO

Really think about what people are saying about the Vitodens. To quote Brad White, "when a Vitodens is installed in a given structure, it essentially can tell you, indirectly, what the actual heat loss is".

It gives Brad balls-on indoor temperature maintenance and he doesn't even have all of his TRVs and he has NO form of indoor temperature feedback.

These are extremely bold statements that I do not believe can be made of any other boiler. THIS IS THE DIFFERENCE!

I like to think that "boiler snobbery" has nothing to do with my recommendations for the Vitodens and has everything to do with my awe for the most remarkable machine I have ever owned. The Vitodens is not however a panacea--it works its best when driving systems designed with its principles in mind and operated in a manner consistent with its goals.

marc friedman

don't forget V's pricing strategy ...

high list price, little discount

Mike T., Swampeast MO

My Comfortrol unit is in the boiler located in the basement quite close to a pair of French doors. The Comfortrol does not sense room temperature.

TRVs on all of my rads. Reset curve adjusted such that the setting on the sun dial (66F) corresponds almost perfectly with the maximum temp I can maintain anywhere in the house regardless of TRV setting.

The only time I ever need to adjust the sun dial is if I need to rapidly raise space temp in some part of the house as with the bare maintenance curve, space temp rise can be extremely slow. You can also press the "party" button for a period of supply temp boost.

Not "black" magic, but at times it does seem almost magical.

The WS remote is nothing but a shortcut to the sun and moon dials and does not sense room temperature. The RS remote is capable of adjusting the slope via sensing of room temperature but is suggested for use only in systems with low water volume and low mass like fin baseboard (or perhaps iron baseboard). "Hydro air" really isn't mentioned in Vitodens literature.

Glen

even though I am a big V nut ----

there is the odd happenstance where a vitodens 200 is not your best bang for the buck. This is a high temp install - why mix apples with pears? Vitodens make the most sense where low temps are needed - and with that type of system will condense like no other. FACT! (sorry George)What about a Vito 100????? and buy your own controls - and pumps and bells and whistles - that way you can play all you want. Or if that doesn't suit your fancy I highly recommend a Vitola - beautiful boiler. Pockets still not deep enough? - look at the IBC boiler from British Columbia - mod con - made in NA. Has some neat features too. Best advise - don't get hung up on a low temp boiler when you don't need one!

rumn8r

Responses to my posts in other threads convinced me that this was not a high temp application and that a mod con would be condensing the majority of the time (except for indirect HW and recovery of pool temp).

S Ebels

Aside from all that........

Here are a few facts...........yes facts, These are based on observation of systems we have installed, servicing of these systems, tearing down each of the brands of M/C boilers we have worked with and consumer feedback. BTW, we use Knight as our "better" boiler, Viessmann is of course, the "best" and it has nothing to do with brainwashing or marketing.

Nuts and bolts type stuff:

If you objectively examine the burner and the HX in any M/C boiler you will find that they are all pretty much the same, except the Vitodens 200. There is nothing that compares to it in burner technology or in construction and material used for the HX. (Read what Perry said about weight. Probably 60% of the difference is in the HX) It is the only MC boiler I know of that will take 1,700* combustion gas and reduce it to nearly the boiler water temp, in a single, 1 1/2" pass. Through a .8mm air gap no less. The Vitodens, given the same care as anything else, will outlast any other M/C boiler that I have had my hands on. I can say this with certainty because it's simply in a class by itself. Anyone who's held a HX from a Vito, Knight, Munchkin or any other M/C boiler in their hands would be stretching to say they didn't agree. AFA the aluminum block boilers go, their life span will be completely dependent on the maintenance of system water quality, simple as that. (Bi annually would be mandatory if I owned one or installed one for someone else)

The operative phrase I have heard from a lot of salesmen, marketing guys, and other folks that sell boilers has been, "It's not the same as a Viessmann but it should work good". This is a true statement for the most part. There are no boilers that are the same as the Vito but there are a number of M/C boilers that will provide efficiency that's as good as the Vito.....in most North American applications. On a system designed to take full advantage of the Vito's capabilities (constant circ/TRV's, medium to high system mass) it will be in a class by itself. No magic about it, that's just the type of system the Vito was born to be connected to.

So what I'm saying is efficiency wise, I would anticipate about the same performance from a Vito or a Knight. Length of service life I have to say goes to the Vitodens hands down.

Now, think outside your box here for a minute and let me confuse you even more. I don't know all the particulars of your job but is a MC boiler the best thing to use for your pool heater? Maybe an alternative would be to use a tankless water heater, ala Takagi or the like, to heat your pool. You get flow activated firing with 10-1 turndown and they only cost 30-40% of the Knight. If it pukes in 5 years, you undo three unions, unplug it, disconnect the vent and hang a new one. It would probably simplify your piping a bunch and save money on controls. Sure you can use a MC boiler to do dang near anything with the right controls but how about the cost of those. Some things can be kept very simple. Just food for thought but you can apply that to your whole system. Use a product in a system it was designed to be used in and it will give you it's best service. Also, why the 3 hydro airs? A/C? Maybe there's room to consider a radiant or panel rad system and use a simpler ducted system for air treatment and cooling/dehumidification. Use one AHU and zone it? I don't know what you're dealing with there and maybe those suggestions are ludicrous. If so, forgive my ignorance of what you are dealing with. I'm just saying that there are usually more ways to skin a cat than just using the knife you're given.


BTW, setback of air temp in a pool room is asking for trouble IMHO.

Enjoy! I love the research and design part of any job. You get to stretch your imagination a lot with hydronics.

rumn8r

Steve,

The Vitodens might last longer than the Knight but it would have to last twice as long based on initial cost if there is no increase in efficiency.

A tankless water heater would add cost because it would have to be vented (already a problem) and would still require a HX with a water flow of > 20 gal/min. Besides, I would already have a high efficiency modulating boiler as a heat source.

Perry_2

Are you sure of that?

There are two cost associated with a new boiler.

The cost of the boiler.

The cost of installation.

It is quite common for installation to cost as much or more than the boiler.

I can accept that the Vitodens boiler cost twice as much as the knight. But not twice as much to "buy and install". Assuming that the installation cost is about the same, and the Vitodens is twice the cost - then the Vitodens would need to last an additional 50% longer than the knight for breakeven.

However, in the end we all have budgets. Whatever you chose - let us know in 5, 10, and 15 years how it works out.

Perry

S Ebels

Rumn8r

I like that handle BTW.........

Like I said, I have no clue as to what you are dealing with on your job. You have to make those calls because you have the firsthand info. I was just trying to suggest that sometimes we all, myself included get hung up on doing something a certain way to the exclusion of something that might work as well or better. YOU are the doctor.

Perry is right on with his comment regarding replacement. The cost of which will be stood by you even if the parts are "under warranty". No heating appliance manufacturers cover labor to my knowledge unless you purchase an "aftermarket" extended warranty. Come to think of it, that's another large + for the Vito. They are by far the easiest MC boiler to service that I have laid my hands on. In fact, that applies to anything Viessmann makes. They are designed to be taken care of easily. In fact, I would strongly suggest that you download the manuals for both the Knight and the Vitodens and compare suggested maintenance between the two when making your decision. You may be surprised.

Initial price is one thing but when dealing with high efficiency appliances of any type, the "down the road" service and maintenance can quickly tip the scale due to servicability issues. More food for thought. Ain't it fun?!!

Paul Pollets

Agreed!

This application would best be served by a cast iron boiler. The major loads are high temp applications. When the Vitodens is installed, the boiler ramps up to maximum fire rate, when the HW coils or heat exchanger are calling. I'd be using a Vitogas 100 or the Vitola with chassis burner.
Sure, multiple Vitodens would work. The increased costs would be hard to recover in this application.

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