code man says my DHW tank has to go as a heat source What now?

Eastman

30 mintues?

The burner runs for 30 minutes and the pump for 20?

morpho

Yup

More or less...Is this a bad thing?

good thing?

Eastman

Look at like this...

The tank fires for about 1.5 hours a day at roughly 66% efficiency. 

1.5 hours  X 30k btus per hour X 66% = 30,000 btus of thermal energy per day delivered into the water in the tank. 



The pump runs for about an hour a day.  Energy is conserved and there is basically no inefficiency loss during the transfer of heat from the tank to the slab.



1 hour of pump time must therefore transfer 30,000 btus into the slab.  In other words, we can say the slab is absorbing energy at a rate of roughly 30,000 btus per hour during each 20 minute pump run.



This rate of absorption actually exceeds the net input rate of your water tank's burner.  (As Gordy mentioned earlier, a 30k burner on a conventional water heater really only creates roughly 20k of usable heat.



What I'm getting at is...  I don't see a reason why you couldn't hook up a boiler directly to your slab.  There are cheap conventional boilers that fire close to this range and I believe include the necessary low water protection loop internally.  For example, the loch copper tube one I mentioned earlier; first stage starts at 23k btus.

Gordy

Problem is

Anything you buy you have to look at your electric capabilities.



How many kWh can you produce, store, and use daily.



Anything that modulates, and condenses is going to use more power than your present setup because there is a fan that has to run for the combustion process. You already cringe over an 87 watt circ running to long. This is your hurdle. So you either need more storage capacity, a genset to pull ya through.

morpho

POWER POWER EVERYWHERE.

Eastman:

Oh, I have no doubts my HWT was not doing the job efficiently especially when it was one of those really really cold nights. But at no point did I find I was too cold or uncomfortable in the house. The heat loss calc didn't take into account passive solar gain...maybe that made up for the underpowered HWT? I don't know.

If it a sunny day (and the coldest days here are always the clearest) the HWT won't come on all day guaranteed! even at minus 30º



So the HWT has to go and I have options is what I am getting out of all this.

ahahahahaha! I am about to go mad.



As a side note to all this dual purpose tank business:

I contacted the government body that oversees all this and they said no problem a dual purpose tank is fine. Then I asked them if I can use it as a stand alone for the floor.

"oh no, it is a dual purpose HWT...you have to have it for domestic and floor.

So I contact the maker of the tank and they so NO! it will actually work better in a closed loop as there won't be a constant inflow of fresh water carrying oxygen, sediment and minerals into the tank. Should make the tank last longer.



Made me laugh because as it is written.... using it as a stand alone wasn't even considered for the code because it says: DUAL PURPOSE...must mean you HAVE TO USE IT FOR BOTH!...at once.



I did that mostly to point out how stupid the rules are.



Anyway....



Gordy:

I have a total of eight 260ah batteries and 2.8 kw of panels...this has proven to be enough to power everything I have with a day...maybe two of back-up if there is a total solar eclipse or the mothership blocks out the sun.

Typically I never get the bank below 65-70% and unless it is a dark day I usually get into a state of float...though dead of winter I am just finishing an absorb cycle then the sun vanishes for another 17 hours...17 long cold dark hours....why didn't my ancestors keep the wagon and ox hitched up for another couple months and headed south? I could have been a vineyard owner swinging in a hammock!



So yes there is the possibility to add a bit more load to the system...how much does a blower and computer swallow up? I contacted Loch today to find out and they had no idea what the electrical load is on any of their units when they are firing up or when they are in standby. Probably not a concern for most people.

I only put the genset to my system 16 times last winter...mostly to keep the batteries from discharging too deeply. (getting down below 50% will shorten the life of the batteries) So I guess I could burn some gas to keep my LP boilers electronics running.....THROW ANOTHER POLAR BEAR ON THE FIRE!



I can safely say a circ pump in a boiler is going to be somewhere around 60 - 80 watts depending on speed. I'm sure I can handle it....as long as the system fires up 2 or 3 times a day for 20 minutes. If the boiler has to operate 20 times a day to heat the floor then no it won't work. (not sure if the boiler will function any differently as far as run times compared to the HWT? I have no experience with a boiler...never even seen a boiler in my life, never mind gotten to know one)



Speaking of boilers....buddy of mine who is a plumber seconded a vote for a Cadet.

Anybody have one? know if it would fit my needs?





Hey, thanks for everyone input on all this by the way. It has been a huge help.

kcopp

Hows this.....

http://www.bradfordwhite.com/natural-gas-combination-water-heaters-atmospheric-vent

Eastman

morpho

I was hoping to illustrate in my last post that a heat source without a buffer tank should work on par with your current tank system.  The inefficiency wasn't really my concern.  The fact that your slab absorbs 30,000btu's per hour for 20 minutes at a time indicates it's a pretty good buffer in and of itself.  I think you might find that your system is too small to justify the cost of condensing equipment, hence the question becomes --can I hook up a cheap conventional boiler and fire it directly into the slab?  That answer appears to be yes --if you can find a small enough one.  Some kind of small two stage atmospheric (no fan) would seem to satisfy your requirements.



A tank based system has other benefits though.  For example, a short burn with a long multi hour pump cycle might actually save you significant pumping electricity.  Perhaps somehow the tank could be forced to fire near peak solar radiation too, so you wouldn't have to store the electricity that runs the burner.  Maybe some today you could hook up a wood stove to it, etc.

morpho

Gotcha Eastman

...I get where you were going.

That makes sense.

Not sure if this would make the code guys happy though....I'm sure there must be something about having heat exchangers or buffer tanks or code approved fairies.....sorry. I am getting bitter about this.

Would the low temp water returning to the unit create condensation or thermal shock?



As a side note about wall hung units:

I have been reading some nightmares online about people experiences with ModCon units and how finicky they are, how they just don't last. So if the thing is only going to last 6 or 7 years lets say 10 at the outside, There is no way any gas savings will make up for having to replace it that quickly, especially after spending the premium bucks on it.



Kcopp:

Thanks for the link. I had a quick look at those as well....most of them are way too big for my little utility room. or maybe I just have wall hung space envy.....and anything bigger than one of those looks too big now

Eastman

boilers and slabs

Slabs have traditionally been the ideal way to buffer an on/off boiler.  Problems with thermal shock, condensation, etc are due to the lack of a boiler protection loop.  People that experienced these problems did not have one installed or configured correctly.  I think many units actually now come with this loop as part of the boiler.(Edit: I think I am wrong here.)  Finally, you would only need a heat exchanger if the radiant tubing didn't have an o2 barrier. 

morpho

one more for the "hmmmm?" file

So while lurking around the intertubes I came across Takagi's website and it says "for space heating"

Not saying its a boiler...not say its ideal either, but why would a major company, now owned by A.O. SMITH put something like that on their website if they didn't make it for space heating and or at least know it would work and possibly have had it stamped as such?



Eastman:

I see...thats what the "Performance loop" is in the Loch 2 stage is about.



Wow, it's a wonder all you plumbers, gasfitters and Boiler experts can keep all this stuff straight in your heads.

morpho

the link

http://takagi.com/?p=applications.php&page_id=23

Eastman

i think so

I haven't looked through the manual in detail, but that's what I would guess.  (regarding the loch) Edit: guessed wrong.

SWEI

Tankless for space heating

if they carry an "H Stamp" they are legal (in the US anyway.)  A good tankless is designed to last 20 years, as is a good boiler.  The difference is expected operating hours (2000 per year on the boiler, perhaps a couple hundred on the tankless.)  The tankless will only deliver its full output with a large (typically 40ºF or greater) ∆T, and modulates its output to a fixed temperature, making it unsuited to outdoor reset control.



Still , it might work in your application -- with a buffer tank.

Gordy

Cadet makes

Is a perfect size boiler for your heat loss 9-40k input

Rich_49

The code man

is a **** .  

Here is my take on a solution that is not too difficult and fits with your lifestyle and chosen setup .

 

Central to this system is a Heat-Flo HF-60-D tank (2 coils) .  Cast iron boiler feeds the bottom coil , water in tank is heated to 180* , this tank is your storage tank and as DHW is used it is mixed down to 115* via a Taco 5000 DHW mixing valve , when heat is required pump ( Dt) with Taco I Series ODR mixing valve on suction side gives you outdoor reset and you only use the required BTU for that moment in time . the heat exchanger for this operation is the top coil .  Control is a high / low limit aquastat that shuts off at 180* tank temp and fires boiler when tank temp is 150* . Both pumps could probably be Bumble Bees that would consume a whopping 44 watts combined when really working hard .

  Just a suggestion

morpho

ok...

SWEI:

Not sure if the tankless is certified...I will call on Monday.

The hours of design use is referenced in their warranty section. Less than 3000 hours for the lower end models and 9000 for the higher end units. I think that is supposed to pertain to the total hours during the warranty period. 5 years on parts 15 years on the exchanger.



So if there is no difference in the amount of time it would run compared to my current HWT that would be roughly 550 hours a year.



Now if for some reason a tankless or a boiler will run more often than my HWT is running then there is no way to know how many hours I might need it to run.

Why would boiler have to run more often than my HWT...any reason?



But it is an interesting way to look at heating the water from a cost of unit perspective.

Even if the tankless craps out the 5 year mark and I replace it 4 times over a 20 year period at a cost of about $500 for the lower end unit...I still come in well under the cost of a mod con that - from what I can tell - probably won't last 20 years and will need to be replaced in that period as well.

Don't even get me started on the waste involved in this method...but you see where I am going with the perspective.



Gordy:

thats onother vote for the cadet. Though I had read a complaint somewhere from an installer that Loch is finicky and I should stay clear of them...



Rich:

Well he isn't a shmuck per-say...he is fine and has been pretty helpful...he just follows the rules that have been laid out...but the SYSTEM IS MOST DEFINITELY A SHMUCK!



I am sure your set-up suggestion would work great....until I looked up the cost of the tank...ya...boiler and then an expensive buffer tank...plus all the other stuff puts it out of my league for sure. ( well aware you get what you pay for....but if you can't pay for it...you can't get it) And then there is the space. I can't have a boiler and a 60 gallon tank..no way. I would have to build an extension off the house to make that happen.



Going to Nicaragua for the winters is starting look more and more logical....

RobG

Takagi

I don't think that the Takagi units have the H stamp. Take a look at the Navian units, they offer boiler only models. Not sure about the pricing. It has an internal pump, I didn't look at the piping diagram but I think it has to be piped primary secondary so two pumps are required. Its max electrical usage is 137 watts. That and a Bumblebee for the secondary might be a good match. They also offer a pre-fab low loss header which would make piping a snap. Here's a link.

http://www.rinnai.us/boiler/product/q85s

Rob  

Canucker

Bumblebee

He may not be able to get that pump. I live fairly close to Toronto, so if its going to be available, it would be here first but every supply place I went to, after they stopped looking at me like I had 3 eyes,(not many of them had even heard of it 6 months ago) said it wasn't being shipped in the foreseeable future to Canada. (it may be available now but I haven't had time to look into it lately)

morpho

mail order

Hey Canucker:

Thanks for the heads up.

What I can't get in Canada, I order from anywhere I can get it.

Warranty be damned!



RobG:

Ya, I'm not holding out much hope that Tagaki are certified for space heating, but it's worth a shot.

Mark Eatherton

Easy fix...

It's not going to conserve any energy, but if you want to get through the winter, install one hose bib on the water heater to qualify it as a "dual use" heater. If asked, tell them it's for washing mud off of your shoes...



From personal experience, I use to use a water heater for heating my house. I even went as far as installing a solenoid valve between the water heater control valve and the burner and installed an outdoor reset control on it to achieve maximum efficiency.



I eventually replaced that water heater with a modulating condensing boiler, and reduced my energy consumption by 30%.



To the untrained people who are reading this thread contemplating using the inexpensive water heaters as a dual source heater, STOP. They are a legionella generator, and unless you intentionally want to expose yourself and family members to this deadly disease, do not consider doing so.



If you want to throw a plate heat exchanger between the source and load, go ahead, but unless you are using a HUGH heat exchanger, expect it to not too work well.



Ask your code official if he'd accept your system if you throw a means of "drawing" hot water off of the tank if he will accept it as is. Just don't draw anything off the tank and you should be fine other than the major waste of fuel..



BTW, FWIW, I totally disagree with the Canadians and the American codes allowance of dual purpose heaters and have proposed a major change to the IAPMO code to disallow it. If used with a plate heat exchanger, and properly piped to avoid stagnation, I have no problem, but I refuse to allow these deadly legionella generators to continue.



The biggest problem you will have with trying to adapt a mod on into your system is the additional parasitic cost of operation, and the fact you will need to set a power conditioner for the boiler because it sees inverted electricity as "dirty" power and will probably give strange errors. There is nko way around that other than going with a conventional boiler, and then done right, it's going to be more expensive than has been quoted. You have to protect the boiler from long term condensation, and protect the floors from too high a temperature.





ME

morpho

Hi Mark

Oh.... man alive!

Is this situation that odd (save for the offgrid issue) that there isn't a well walked path in regards to a boiler choice and installation method for a smallish BTU load?



I FULLY appreciate the point regarding the health concern. I think it would be foolish to have a system where your domestic and space heating water are one in the same.



My preference would obviously be to not have to plumb the HWT into any kind of water supply at all and keep it as the stand alone closed loop system it currently is. Period.



I am fully open to installing a boiler, as long as it will do the job I need it to do and not get destroyed because it's not meant to do what I need it to do. But from what I can figure out, with the kind help and input of a lot of folks here, is that there really isn't a boiler to do it with. Save for a couple of options (2 stage boilers, or, if I am understanding this correctly, a slightly overpowered boiler with a heat exchanger.



My actions and desires are not to circumvent the codes, but the interpretation of the dual purpose HWT as not suitable as a single use heat source is utterly stupid.



Plenty of those dual purpose tanks are being used for just domestic hot water. How is this not in contravention of the stated purpose of the tank as "dual purpose"?



If I can't use it as a stand alone heating appliance and must have domestic hot water as well, how can you use it for domestic water only with no questions asked?



So, silly interpretation aside....I am totally fine with getting a boiler.

I have talked with plenty of local plumbers and they either have no answer for me or want to set me up with something I can now guarantee will fail. ( thanks for all the info everyone, otherwise I would have a massive cast iron system in here doing all sorts of stupid things ) So it sounds like a cast iron boiler will be more expensive and complicated than expected if as you say: "if done right" And I have no desire to not have it right. SO what does this critter look like? How do I protect the boiler from condensation and the floor from too high of a water temp?



As far as a ModCon and the "dirty power" I need to check with my PV guy as this is a pure sine inverted system, so in theory it should be fine with the boilers electronics...but it sure would suck to find out it doesn't play nice after buying and setting it up.



In your opinion, electrical power aside, is the modcon the way to go?



I have always been proud to say I have never been in debt in my life. If I want something, I work towards it then pay for it. I saved up for a very, very long time to buy the land and build this little cottage. I did without so many things over the years that others had so I could do this. I have been free my whole life to do what I want simply because nobody is holding anything over me. Maybe I need to go hat in hand to the bank for the first time in my life and borrow the money to do this... whatever "this" is supposed to be.



Hey Mark, thanks for your input and thoughts on this.

Mark Eatherton

If it weren't for your power issues,,,

I'd absolutely say that a good fire tube modcon is THE way to go. It has the ability to modulate its output down to match your load, but therein becomes the parasitic power consumption issue. The longer it runs, the more precious KW's it eats, Granted, with DCECM circs your power consumption per function will be less, but still there none the less. The inducer fan on the boiler is a DCECM motor for what its worth.



With it being a single zone, you could find an atmospheric of 50K (Burnham and others), but it won't have the ability to modulate, so it will short cycle, and the hardest thing you can do to ANY piece of equipment, is to start it up. This would require you to add storage (buffer tank) in order to give extended ON periods, and extended OFF periods and with your mechanical room being so small, probably not enough room to accommodate a tank large enough to make it worth your while.



Not exactly sure of your set up, but you WON"T be able to use the existing venting system and will have to run an approved plastic vent for the modcon boiler.



I've been told by numerous manufacturer's that a battery back up UPS is the least expensive power conditioner available for applications like these. It has been a while since I've attempted using anything with PV, so Id check with the boiler manufacturer and the inverter manufacturer to make certain they play together well,



If you did decide to go with a cast iron atmospheric, the best way to protect the boiler is with the use of a thermostatic bypass applied to the boiler inlet (Danfoss /Termomix makes one) and a 3 way non electric thermostatic mixing valve to protect the floor from too high a temperature.



It's not rocket science, but most inexperienced installers think its as simple as throwing the cast iron, or copper fin tube boiler in and turning the operating limit down to 140 degrees F, and for the most part, that WILL work, until the heat exchanger fails due to long term condensation exposure. And you still have to deal with the short cycle inefficiency issues.



The nice thing about a cast iron boiler, if wired to a line voltage thermostat, there is NO ghost power consumption. You can't do that with a modcon. At east I've never tried to do that with a mod con...



You have some decisions to make here.



BTW, it (the problem of dual use) actually has roots in the ANSI standards. Your local AHJ is just enforcing it as written. In order for it to be called a water heater, it MUST have water being drawn off at a tap., hence the reason for a tap. You can still have to pressure reducing valve, blah blah blah, but it MUST have a means of drawing tao water through the device. I agree, really a silly law, but theirs is not to wonder why, theirs is but to enforce or die.



ME

morpho

Yup...I certainly

do have some decisions to make.



Is your sense that a ModCon is going to last long enough to make it worth the expense?

If it lasts only 5, 6,...10 years and I need to get another, then that is pretty bad investment. I am pretty wary of electronics and if I can avoid them, I do...but sometimes they are unavoidable.



Maybe I should stop shaking my cane at all the hip kids and their flippy dippy flashing light technology and join the parade.

Mark Eatherton

With proper maintenance...

a good modcon will last 15+ years. With improper maintenance, it could fail within 5 to 7 years.



Even the atmospherics have solid state electronics on them. I believe they MUST have an outdoor reset control at a minimum.



An atmospheric with a 2:1 turn down is not an efficient machine, because you can only turn down the gas input, and not the combustion air. Doing that causes the combustion numbers to go upside down due to excess air, and your fuel costs can go up.



Figure on about $300/year for maintenance into your long term program. After the first year, it may be possible to extend the service to once every 2 years, but no longer than that. That is without a doubt the biggest downfall of modcon boilers, No one (very few people) are servicing them...



ME

VA_Bear

What is the code problem?

In my area, the inspectors have to reference the code requirements that cause a failure of an inspection. Does your notice of failure say anything about the code section(s) that were a problem or a narrative of the the reason(s) for failure? The problem here with sharing a single hot water source for DHW and space heating is the isolation of the drinking water from the space heating water. The only system I know of which is authorized to share water is the Apollo system, which uses a 75 MBTU water heater to supply a hydronic heating air handler with a DX AC coil for cooing. That water heater has side taps for the heating coil connections and the heating loop is drinking water safe.

Gordy

Morpho

Mark is the professor of hydronics.



Kind of humbled by the hose bib trick. Give it a try can't hurt. Sometimes tend to over look the obvious, and simple fixes.

morpho

no official write up about the HWT

Gordy:

I kinda got that impression about Mark...there was a warm glow to his post and I thought I heard the hiss of steam when I clicked on it.



VA_BEAR

I was not red carded in any official way, Like I have said, the code folks have been cool about the whole thing. I got a heads up that I was "going to need to change this before we can pass this" kind of warning. I am the one who set this up so it is my fault %100

They just said the HWT is not certified as a space heater and must be replaced with a dual or boiler. Like I said in the beginning, I don't understand the reasoning with this kind of set-up or even why a code approved tank that is only used as space heat can't be used.....ahhhh never mind! this is a circle that just gets tighter and tighter....I will get a boiler.



Just a question:

Every installation diagram I see has a buffer tank or a heat exchanger, I have yet to see a diagram showing a closed loop and a mod con boiler without a buffer tank.



Okay, I am going to bed...I've been dreaming about this stuff...so I am dreading going to sleep.

Eastman

Disagree

With the utmost respect for Mark's professional opinion, I feel obligated to present my own hack amateur analysis that I believe leads to a complete conflict with the general thrust of Mr Eatherton's thesis.



Morpho's observations indicate that his system requires roughly 30k to 60k btu's per day.  This equates to a heat source with a peak output of 2.5 thousand btu's per hour.  Perhaps Morphos' observations are off by a factor of two.  That implies a peak output of 5k btu's per hour.  These numbers are substantially below the output minimums from any modulating heat source.  What then, is the point of paying for modulating technology?  His system isn't short cycling now, despite an output of roughly 20k from the tank heater.  In a previous post, I also laid forth evidence indicating that his slab is capable of absorbing and buffering significantly higher thermal outputs (30k btu's per hour) at relatively low temperatures.  At what heat loss can one say  "you know, the payback just isn't there"?  Surely Morpho's current operating costs are not too much more than the suggested maintenance budget of $300 per year for a modulating heat source?

morpho

I'm freakin out

I'm going to go rock back and forth in the corner of my utility room for a while.

Eastman

That's where...

I post from.

Gordy

assumptions based on assumptions

Why over think this. Unless Morpho wants to share we dont even know how many winters this system has worked through.



What may be just fine for him to get by for comfort with his present set up may not be to you me, or anyone else for that matter. I think mostly he would like to make what he has work,



I tend to believe if putting a valve on the water heater in some believable fashion to make it work for dual use Morpho will have a waterheater for a boiler till it craps out.







And Morpho are you confusing buffer tanks for an indirect water heater in the diagrams you are looking at?

Mark Eatherton

You are WELCOME to disagree with my assertions....

Eastman, it is civil discourse like this that makes the Wall such a great place to hang out. Each one teach one and everyone learns from the experience,



The problem that I see with your analysis is the time weighting factor. TBtuH capacity divided by too many hours. The other thing that happens in reality is significant overshoot and undershoot of the slab, and then the flywheel mass effect kicks in and completely takes over, giving new meaning to the term MEAN radiant temperature.



Your assertion about the slab being a significant mass is correct, and improperly controlled, it WILL result insignificant deviations in the room temperature. If these deviations are acceptable to the end user, then so be it. It is not acceptable in my book and doesn't fall within my definition of true comfort, which is also subjective, and probably isn't the same in my camp as it is in yours, or other folks camp.



For the record, my definition of comfort is not being aware of your surroundings. You are not too hot, you are not too cold, you are not under humidified, nor over humidified, and you are neat hearing any noise associated with the delivery of heat/coolth into your environment, Simply stated, if you can achieve these conditions, you are truly comfortable.



Obviously, it varies form person to person, but that is the mantra I've run large companies with and it has been proven to be successful.



Having had lived with this tank style water heater, I can tell you that due to the slop in the thermostatic control valve, and the lag in transfer and pick up that I did experience significant deviations in comfort. Rarely was the home perfectly comfortable with just the tank stat in control. I tried continuous circ in an effort to smooth out the bumps, to no avail, hence the reason I (illegally) modified the heater to allow for the application of an outdoor reset control. Been there, tried that and have scars to prove it. Also, for the record, the controls I applied to this tank could NOT turn the operating temperature any higher than the tank control would allow, so it was therefore not unsafe,



With a high mass system, with the tube in the bottom (is it really possible to keep the tube within 2" of the emitting surface?) of the slab, this compounds the problem of under/overshoot. By the time the heat finally makes it to the surface, and starts satisfying the thermostat, and the thermostat eventually shuts down, the slab has a SIGNIFICANT amount of heat that IS going to come into the space, and when it does, will result in fairly significant overshoot, resulting in people standing around in their underwear trying to keep comfortable.



As has been stated by John Siegenthaler, myself, Robert Bean and numerous other hydronic comfort prognosticators, in order to achieve perfected comfort, input must equal demand in a real time basis, not averaged out over 24 hours. OK, I added the 24 hour thingy, but I think you get my drift. As for appliance sizing, industry standards dictate that the output capacity of the appliance MUST equal the heat loss calculation.



The big problem there is that NONE of the heat loss calculation programs take real life into consideration, like internal gains, solar gains and flywheel mass effects. In my own home, the load calculated out at 100 K butH. I decided to try an experiment in my own back yard, and I installed a 50K btuH heat source, and I have lived with it for over 10 years now, and have seen"design conditions" and below MANY times, and I've stayed perfectly comfortable. I've also never seen my modcon doing more than 80% of capacity under those worst case conditions... Would I ever consider doing something that brash for a customer? Not in your wildest dreams. I can't afford the liability.



As a professional, we ALL must adhere to the rules, otherwise, we can be placed in a very compromising situation that WILL cost us money out of pocket.



To my knowledge, 40 or 50 K is the smallest modcon appliance available. That's the bad news. The good news is that the ANSI standards used to reference the minimum turn down capability are finally being updated, and turn downs of 10:1 are being allowed, resulting in minimum output capacities of 4 or 5 K btuH. If this exceeds (significantly) the demand being imparted on the system, then the addition of a buffer tank to allow the btu's a place to park and standby is generally used to avoid short cycling,



Now, if you and Morpho are not hydronic professionals, it's your castle. So long as you don't create an unsafe/unsanitary condition and the work is in compliance with the code being enforced, you can do whatever you want. But if your selling the home, then it is once again subject to the scrutiny of home inspection professionals, and they may call your practices in to question, and require some sort of compensation for potential changes.



Morpho, I assumed you had a "dual" use appliance, approved for that application in your home. If it is not, you will have to purchase an approved appliance, and then throw the drain valve/tap at it to comply. The "approved" dual use heaters are more expensive than a regular tank type heater. That rule is consistent on either side of the border.



In reality, with an existing home, I'd recommend a detailed heat loss calculation be performed, AND a blower door test also be done to verify the one wild card factor we ALL have to live with, that being infiltration. One you have THAT information, then we can comfortably discuss how big it needs to be. Otherwise, its a lesson in futility :-)



ME

SWEI

Is it really possible to keep the tube within 2" of the emitting surface?

If the slab is reinforced with bar instead of mesh, and if the bar is on chairs, and if the tubing is tied to the top of the bar, then yes.



Otherwise, probably not...

Eastman

in complete conflict

Yeah, these discussions wouldn't be very entertaining if there were never any dissenting perspectives.

archibald tuttle

joining the foreign legion-ella

mark.  if i read this correctly, you are suggesting not to use the water heater as fully dual use in the sense of providing your domestic water, but rather to provide for a rinsing tap that would qualify the installation, but use a separate system for DHW.



I get the idea of mixing long resident water with domestic, even if the piping is theorectically 'watersafe' from a consumptive perspective has possible consequences because of the dwell time and the recirc means you are not really fully purging or drawing new water each time, not to mention that there might be other implications depending on the air content of the water for getting airbound or corrosion.



i'm with you, if i have interpreted you directly, to make the water heater conform nominally but use it for heating.



and it wouldn't surprise me that you did get 30% savings in fuel going from simple atmospheric water heater to modcon, but given his small btu requirement and limited electricity, i'd think the setup he has is quite economical and appropriate and the payback on the cost of a mod con or really any sophisticated heating appliance would not be there even if the unit lasted the expected 15 years or more.



brian

Mark Eatherton

egg zachary...

Just bring it into compliance by adding a tap, but not actually using it for DHW. I agree about the economics. Hard to justify, but some people want to do the "right thing" environmentally, at almost any costs (think solar thermal, or solar PV), and setting a mod con would significantly reduce his carbonaceous foot print for a lot less money than doing solar...



Thanks for joining the revolution :-)



ME

morpho

So...

Eastman:

You nicely condensed my concern about the modcon not being the logical choice in this application. If only for the cost to buy and then maintain it. Not to mention the unknown longevity, the possibility that it burns itself out through short cycling etc. But the size...oh the little bugger would clean things up in that room a lot! Not worth it I know...if space were the only concern I could literally blow out the wall and make a 3 foot extension for a massive 100 gallon water heater and it would cost less than a modcon.



Concerning the cost of running my current system v.s. $300 dollars for modcon maintenance year. What I am paying is inflated because I am paying for NON bulk propane and so for two winters it has been about $795 a year to heat the place. BUT! if I can get the system approved I can buy bulk propane and it will drop to $400 and that is with the old hot water tank. Add something a bit more efficient and it will drop further. Oh I like the sound of that.

morpho

Gordy

You make a good point.

What has been comfortable for me for two winters might not be for another. All I know is that I have not been cold....so I am happy...I mean if I can step out in the dead of winter and lose my fingers and ears in under 15 minutes and I step back into my house and it's toasty...I am not going to complain.



I have to replace this unit with an ASME H certified unit if I decide to go with a HWT.

And yes I will have a water heater for a boiler until it craps out.

Or if I get a boiler, some would say I have a boiler as a "Hot water heater" until it craps out.



Though I am not sure why the hwt would crap out any faster than a boiler in my specific situation. If it is turning on for an hour a day, this would be pretty typical use, if not under for a single family's HWT with three showers, laundery, dishwasher etc. So the stress on it seems minimal to me.

morpho

Mark

The system is triggered off the floor temp.... Usually set to 71...maybe 73 when it's really cold outside and to be honest I have never felt any major swings in temp. The floor is set to 71 and the inside air temp is usually about 68 or 69.



I should mention that I have plans to instal a small (if I can find one..hahaha..) Wood stove as well to "take the edge off" on those really cold nights. Want this really badly: http://www.unforgettablefirellc.com but they are costly. But they are super small and have near zero clearences.



This is as detailed a heat loss calc I could come up with. The likelihood that a blower door test could be done here is zero. I would have to pay someone from the nearest city to drive 3 hours to do it and my guess is I could probably buy a back-up boiler for the price of that service.



I feel like I should go back to school and take Engineering....except I have found myself using my fingers a couple of times on the little math thing on this site they make you do before you post...so engineering is probably not in my future. hahahahaha....

Armand_Colorado

my limited personal experience

I have heated my 3500 sqft 1891 house and DHW (Elbi indirect) for 10+ years with a Takagi M1 with no problems. It is true that the Takagi takes a head loss, but the total energy usage and cost is relatively low. I have tried 2 ways to push water though it: zone pumps + DBP valve between the in/out manifolds; and dedicated boiler loop pump with a DBP. I haven't crunched the numbers for cost efficiency, but I think the latter works a little better and I can let the manifold flow without impedance.



My system is high mass and the small circulators are running much of the time in season. I have another similar installation, using a Takagi D2, that has been running for a few years without complaint. The engineering and controls are simple, inexpensive, and reliable. I am actually replacing the M1 for the H3 199k max BTU condensing ~95%. They cost about $1200, including control/monitoring panel. I'll keep the M1 as a backup but I think I got value from it (about $1.50/month capital cost for active service).



MY THEORY is that these units have been running open loop with all kinds of water, everywhere in the world, for literally millions of people. That is a tall order, so asking it to run long-cycle, closed loop, is not a big deal. Maybe it is an economy of scale that seems to beguile some - that something much cheaper could actually be better, at least in some cases?



My reason for posting is only to share personal experience, since I have learned so much by reading others'. The motives of my choices may not the same as for others, particularly professionals who specialize in hydronic systems. In my case, I chose to invest in better engineering instead of expensive products.