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

morpho

SWEI

Ya it probably is possible to get them in the centre of the slab, but it didn't end up that way in my case. I know they ended up close to the bottom...still seems to work okay for me.

Armand_Colorado

my limited personal experience

removing double post!

morpho

Mark

I stand corrected. The room temp is a pretty consistent 70 according to the lady of the house...who keeps way better tabs on the air temp than I do.

morpho

Armand_Colorado

It's funny you mention Takagi today.

They called me back and confirmed they have two units that are ASME certified, but they are WAY too big for my purpose at 380,000 btu's and 14 gallons a minute. Though I don't doubt any of the smaller ones would do what I need them to do starting at about $600. They also said the return water temp max would be 160....way way over my typical return temps of about 85- 86 -87 ish.

Armand_Colorado

sorry

Yeah, my experience probably doesn't help you, except to the effect that what works does not always conform to what the lobbyists convince the bureaucrats to foist upon us. On the other hand, you can buy a very decent new or used boiler on craigslist. For example, here in the Denver area, there are a couple of new and near-new Lochnivar Knights between 1-2 kilobucks.



On the other hand, the cool thing about the Takagis, et. al, is that the common wisdom regarding over-sizing and cycling does not directly apply, since they modulate extremely well for flow and heat demand. I had to seriously rethink this myself since my first experience in heating was to reform ancient steam systems, which BTW, I think are under-appreciated.

Mark Eatherton

Always wise to check with the "thermostat" of the family....

Cause if momma ain't happy, ain't NO BODY happy...



I suspect that the reason for your temperature stability is the fact that you are referencing the floor temperature, and not the air temperature. Good move on your part, and too bad that others don't utilize the same logic. Your tail (radiant floor) is wagging the dog (MRT).



What usually happens in a passive solar heated home is that the early morning cold calls for heat from the air temp sensing thermostat, and the heat starts making its journey from the LP tank all the way into the slab. At around 10AM, the solar gain starts getting stronger coming through the south facing windows, and the air sensing thermostat gets satisfied, BUT, there are still a BUNCH of btu's in the slab that ARE going to come into the room, and cause the room to over heat, and people to shed clothes, or open windows, or turn on air conditioners (seriously).



This is usually more of a problem in the dead of winter due to the incident angle of the sun in comparison to the vertical glazing.



Obviously, your experience may vary :-) But I have been involved in many forensic situations of discomfort that were caused by this regular condition.



Another negative we didn't talk about in using a tank style water heater for high mass systems is the rusting out of the flue liner. People assume that due to the fact that their water heater may see incoming water temperatures as low as 40 degrees F in the winter, that running it continuously at a lower temperature is not detrimental to the unit.



Bare in mind that the typical duty cycle of a DHW heater for heating DHW is less than 2 hours per day. When applied as a space heater, you WILL experience the production of condensation in the flue gas passage ways, and its not real evident because you don't hear or see any evidence of its occurring, but it IS occurring, and the flue gas passage ways are taking the brunt of the hit. Just guessing, but I'd bet that unless you experience pilot outage, you've never looked inside the combustion chamber to see how much rust is piling up on the top of the burner. And because of the fact that the appliance is actually running longer as a space heater than it is as a DHW heater, then its life can be anticipated to be less than it would be as a potable water heater. But at the lesser expensive replacement cost, they are considered a "throw away" heater. It fails, you throw it away, and replace it with another.



One good thing about the application, is that you are NOT exposing the tank to continuous supplies of fresh oxygenated water (unless you used non barrier tube in your slab) so the tank will not rot from the inside out.



Now, you probably know more about your water heater than you really wanted to.



Keep that "thermostat" satisfied at all costs :-)



ME

morpho

Armand...

No, it helps tons.......other than...I can't do it because of the codes.

This is life though.

Armand_Colorado

there is a smaller ASME model

Mo,

I am not necessarily advocating Takagi, since my experience is pretty limited, but they do have the T-M32ASME unit for about $1200. It is 240K BTU and ~83% efficient. Just don't run very hard water and you'll be fine. I don't know how they estimated the increase in return temperature, but you controlling the flow and output temperature is easy. Probably a dumb question, or I missed your explanation, but are you sure you need ASME for a tankless less that 200K?

Armand

morpho

If I am forced into using a HWT

Any insights about how different hwt's would function in my situation?

As in:

lets say I put in a

25 gallon

76,000btu

Recovery of 82 gallons per hour @90º

with a first hour delivery of 155º



v.s.



my current tank:



40 gallons

32,000 btu's

recovery of 25.5 gallons per hour at 100º

No idea what the first hour delivery is



Would I be wasting more propane?

Would it be able to keep up with the demand?

Would it be overpowered?



Any insights about what size power would work best.

morpho

tankless

Hey Armand,

They didn't send that spec sheet to me!



Hmmmm?



So Armand…any insights on what it takes to make these units work?



The Asme H certification is required for the code folks.

Apparently if I have a candle under a teacup and I call it a space heater it needs an ASME certification.



Thanks again.

Eastman

This is for

heating the slab, or for domestic hot water?  I mean, are you looking for a dual function tank that will be actually taking on the responsibilities of your current instant hot water heater?

morpho

Mark

hahaha…yes it is important to keep "she who must be obeyed" warm and happy.



The passive gain has never made me feel uncomfortably warm…yes it does get warmer in the dead of winter..but not overly warm…and it's winter and anytime I can get free heat in winter I will take it.



Question for you mark:

When you say: "People assume that due to the fact that their water heater may see incoming water temperatures as low as 40 degrees F in the winter, that running it continuously at a lower temperature is not detrimental to the unit."



When you say continuously, do you mean for hours and hours? Because this simply isn't my experience. My water heater logs an hour or an hour and a half a day.



Would you expect my system to be creating excessive condensation if I have the tank temp set to about 120ºF maybe a bit lower and once enough water has moved through the system and the tank has been forced to fire up to heat the incoming water the temp settles out somewhere around 95 and the returning water at about 83-ish.



I actually look at the combustion chamber a lot! I have to….I run the thing off a 40lb LP tank and I need to shut it down, replace the tank, re-light it. So I'm looking in there all the time.

But I am going to look extra hard now.



When you say it's good I'm not exposing it to fresh oxygenated water and that the liner shouldn't rot from the inside it peeked my interest regarding non o2barrier pex. Are you saying that the o2 that gets in through the pex can exceed the oxygen in say... city water supply into a tank used for DHW?



Yes I know more about all sorts of things than I ever really wanted to know…thanks to this place.

morpho

Eastman

the tank v.s. tank is for the slab.

morpho

nope just the floor

I can't even wrap my head around any more than that at the moment.

Armand_Colorado

Here's one idea

You'll need 120 for the Tak, but not much draw, compared to the pump. It will require a little more pump pressure than before if in the same loop. I'd consider cranking up the output temp and use some sort of external storage tank, like an indirect DHW, to keep it from cycling too much. Then you can pulse the pumps, saving electricity. It wouldn't be hard or expensive to have a loop between the Tak and the tank, then a loop for the slab, making it super easy and cheap to control.



That setup would probably require:

- indirect DHW tank or your old DHW heater as the storage

- small pump

- aquastat

- mixing valve, if indirect DHW

Eastman

If they are both atmospheric...

I would suspect the higher btu model would have a significantly higher standby loss up the flue.  They are both undoubtedly much too overpowered, but there's nothing really in your btu range.

Armand_Colorado

One idea

Here's one idea

You'll need 120 for the Tak, but not much draw, compared to the pump. It will require a little more pump pressure than before if in the same loop. I'd consider cranking up the output temp and use some sort of external storage tank, like an indirect DHW, to keep it from cycling too much. Then you can pulse the pumps, saving electricity. It wouldn't be hard or expensive to have a loop between the Tak and the tank, then a loop for the slab, making it super easy and cheap to control.



That setup would probably require:

- indirect DHW tank or your old DHW heater as the storage

- small pump

- aquastat

- mixing valve, if indirect DHW

Mark Eatherton

Answers to burning questions...

Your house is an anomaly. Your system is also an anomaly. My house is a regular, well insulated home, but not a super insulated home. My physical plant sits about 10 feet away from my office, and before I "modified" it, it would run and run and run. In fact, it ran so much, during periods of the day that solar gain was at a maximum, that I "modified" it.



I suspect your water heater is one of the newer FVIR models, and accessing the full burner for inspection and clean out can be a fairly large task. If you can get into the physical combustion chamber, look on top of the burner. THere is usually a nice pile of rust on top of the burner. This is the 1/4" thick flue pipe flaking off and accumulating on your burner.



The production of condensation is a function of return water temperatures, and time of exposure. If you are returning at less than 140 degrees F (lower for oil) then condensate is being produced in significant enough quantities that any metal components will be degraded over time. If the flue pipe is made of certain types of stainless steel, it is less susceptible to the corrosive tendencies of the carbonic acid produced. To my limited knowledge, no one who makes an atmospheric tank style of water heater utilizes a stainless steel pipe for elimination of combustion products. Bottom line, the ONLY way to avoid the production of condensation is to keep the incoming water above 140 degrees F.



As it pertains to oxygen diffusion through the walls of plastic tubing, this is probably the second least understood principle of hydronics. (Understanding the PONPC's affect on a circulators function is first). Common sense says if water can't get out, how can oxygen get in? Trust me, it does. Mother nature despises any imbalances in anything. Temperature, pressure, thermal energy and oxygen. When there is less oxygen on the inside of the pipe than there is on the outside, she does everything in her power to make them the same content. Even plastic tubing WITH an oxygen barrier will eventually balance out its oxygen content if it (the fluid) sits still long enough.



The lower the operating temperature, the tighter the molecules in the plastic pipe, the slower the diffusion.



Some plastics diffuse oxygen through their walls faster than others do, and the addition of an EVOH barrier slows the flow at higher temperatures, but its still going to experience diffusion, The only theoretical way to stop it is to use a metal oxygen barrier, hence Pex- Aluminum - Pex, and some other rubber compounds that use aluminum or mylar for its O2 barrier.



Even a full copper/steel pipe system will experience diffusion through its valve packing glands, rubber expansion tank diaphragms, rubber pump gaskets, etc.



Remember, rust never sleeps :-) And oxygen despises imbalance, and is continually looking for something to react with (oxidation) hence why rust never sleeps... It's a viscous circle, I'm tellin' ya.



We attempt to control the process by putting something in the water tank that is easier for the oxygen to eat, that being a magnesium of aluminum anode. Oxygen looks at the tank and see a softer, easier to eat metal (magnesium or aluminum) and decides to follow that path of least resistance. Problems start when the anode is completely consumed. The hungry oxygen then turn to the next harder metal to consume, which is the steel tank. So IF you have non ox barrier tubing, AND you are using a conventional glass lined steel tank (it is impossible to guarantee 100% glass coating,hence the need for anodic protection) then you should be inspecting and replacing the anode on a regular basis.



Now you (an everyone else reading this thread) know even more about your system than you really wanted to :-)



I forgot to add some thing to make you laugh. Do you know what ASME stands for? Officially, American Society of Mechanical Engineers.



Un officially, there are two meanings. Always, Sometimes, Maybe EXCEPT, or as you are going to find out, A Substantial Monetary Exchange... Have to give credit to some of my students for the last tow daffynitions... Enjoy!



ME

archibald tuttle

is that like eggs benedict

Mark,



thanks for keeping track of all your threads.



as you might be aware from frequent, if hopefully not too snide by half comments, i'm not an any price kind of guy when it comes to carbon footprint.  i'm pretty sanguine about the future of humanity (despite the shortage of plumbing techs being discussed elsewhere, http://www.heatinghelp.com/forum-thread/147454/Were-falling-behind -- after all, defending the health of the nation . . . but i digress).



i kind of treat with carbon the way i treat with swordfish.  when everybody else stopped eating it that meant more for me at a better price.



so it is still expensive, there are incentives to cut down but your precise point, that a mod con would be a more cost effective way than solar is the kind of thinking i appreciate in that realm rather than less carbon at any cost approach that is crippling european industry and we're trying like hell to shoot ourselves in the foot here.  Including by the way the war on industrial coal.  color me silly, but i still think that advances in efficiency and pollution control for coal are better obtained at the industrial level rather than at the dispersed home carbon consuming device. that may be because home consumption of coal has gotten more passe and if the same attention were focused on the coal stove or modern coal boiler similar improvements as against efficiency and real pollutants might obtain.  but given that coal is not a fluid or gas I tend to think these savings better realized in an industrial setting.  that said, maybe coal ground could work in pellet stoves, although i think it would be dusty and they aren't facilitated for ash removal -- but maybe they could be.  gotta keep an open mind.



whereas natural gas has proved particulay conducive to improvements in small dispersed combustion units. NG is concedely plentiful thanks to the blessed technology of fracking (which has been with us almost since oil drilling began, it is just lately a target of those who hate carbon based energy), but moving to consume any and all surplus in electricity generation will eventually place home heating in competition with industrial use as it was B.F.   (before fracking -- i know i'm back to the popular conception that it just started a decade ago) So having a policy that sets up a redux of this competion where people were buying coal stoves to heat their homes in preference to gas (and fuel oil which is competition with our industrial transport fleet) and we were talking about importing instead of exporting liquified natural gas and still we were marching toward massive industrial consumption of natural gas in electricity generation with emerging anti-carbon regime.  don't hold your breath waiting for peak oil, but when it really is less available, lower carbon technologies will flourish in true competition.  (And of course i fully support anyone who loves technology but doesn't like carbon in making their own decisons to decarbonize at their own expense).



but of all stupid things for government to stand in the way of simple tech this guys is employing.  look at his house compared to al gore's and tell me who is more of a champion of the environment and has a smaller carbon footprint regardless of whether he's using an atmospheric gas burning device.  and indeed, for many in canada who aren't off the grid, they could run electric hotwater heaters off the copious hydropower.



Brian



PS - funny this should come up.  just had a guy over the border in connecticut who wants to put radiant in his own house (he's a builder himself, but doing a complete gut/remodel on a house he bought for himself 10 years ago and never got to so he and his family are still living over the garage at his inlaws (don't get me wrong, it's a big garage and a pretty nice place)

.

So he is on a limited budget and had heard from his HVAC contracter about the idea of using water heaters to run the radiant and figured he could save the 3, 4 maybe 5 grand over his ideal mod-con plant and just throw in a couple $250 electrics and thus focus his resources on spray foam insualtion on the inside and radiant install underfloor while gutted and once he had recovered from those expenses, he could get his final plant.  since it was his HVAC guy who suggested it, i imagine that the inspectors in connecticut are a little more rational than those in canada on this subject but any info would be appreciate since i told him i thought it was a great idea.

SWEI

The blessed technology of fracking

was called hydrofracking and used water as the frack fluid.  It was frequently used to improve production of water wells.

 

What we're injecting now is creating much more than "a target of those who hate carbon based energy."   If it wasn't why would we need all those loopholes exempting it from regulation?



This discussion would be more appropriate in a separate thread.  Want to start one?

SWEI

DHW heaters (tanked or tankless) as a heating source

It is actually possible to make these work efficiently and safely, but by the time you add the motorized mixing valve, buffer tank, and controls necessary to do so, it's going to cost more than a mod/con.  Really.

archibald tuttle

glad to take this out in the hall

i gotta go work for a living.  can only defend so much 'study' time each day.



got this **** cavernous old boiler with a conversion and its got a nice draft relief in the piping but the pilot keeps blowing out.  safety rod is fine. driving me nuts to the point where i may have to break down and throw a carlin EZ gas on it.



house is slated for demolition in a year so i've just been lighting the pilot and it is never consistent.  stays lit on windy days and then a week later with no apparent reason its out.



anyway i gotta deal with that so not sure which forum is appropriate. obviously fracking has been used for water wells, and long used for oil wells.  and surprise suprise when they are trying to get fugacious oil and gas bearing emulsions and brine they use a little bit of oilly products in the fracking mix and everybody has their own secret slipperystuff, but i don't get too worried about putting oil into the oily ground where oil is.





brian

morpho

Hey SWEI Huh…probably right..but

It might use less electrical power..which is still a concern for me.



Question for you…or anyone…

I have a tankless I use for my domestic use, I have it set to 120º and it does a great job at doing that. I can turn it down incrementally.



So, if I decided to use a tankless as a stand alone for the floor, why would I need to add mixing valves, buffer tank etc. If I need 100º water, I dial in 100º on the tankless and pump it in a closed loop.



If my current HWT system pushes 100º water through the floor and runs for 15 minutes, bringing the floor up to the set point, how is a tankless any different in this function? (not saying there isn't a reason. the longer I am here on this forum the more I am clear I have NO idea what's going on)

morpho

the wording that has me stumped today:

This is a portion of the code that references that the heating unit must be "CERTIFIED".

My question is what does "certified" mean? Is there a specific certification from "XYZ" organization regarding dual use water heaters? (Storage or tankless)



•••••••••••••••••

COMBINATION POTABLE WATER / SPACE HEATING GUIDELINES



Combination Water Heaters shall be certified and marked “Suitable for Water (Potable) Heating and Space Heating”



These systems consist of a Certified Combination storage type or a certified instantaneous potable water heater used in conjunction with a fan coil heating system, baseboard system, and/or a radiant slab heating system, and intended for space heating applications of not more than 75,000 Btu/h.



1 Definitions:

Certified – (with respect to any appliance, accessory, component, equipment, or manufacturer’s installation instructions) means investigated and identified by a designated testing organization as conforming to recognized standards, requirements, or accepted test reports.

••••••••••••••••••••••••••••••

So if Takagi puts suitable for DHW and space heating on their website, does this mean they have certified it?



This unit is advertised on the Takagi site as dual use, but all those fancy certifications on this spec sheet don't mean diddly to me.



http://takagi.com/download/product_specifications/JR2-IN-Rev-0.pdf



So if the code folks just say it must be certified…well I see all sorts of certifications on the spec sheet, so it has been certified….Then Takagi slaps a sticker on it saying: “Suitable for Water (Potable) Heating and Space Heating”. are we all good?





What does an ASME H pertain to?

ASME LHW?…or maybe it's HLW…this stamp shows up on a few things as well.

Gordy

You have to remember

Morpho,



The forum is dedicated to doing things right, according to codes, proper design practice, with the utmost regard for an efficient heating system for hot water, and steam heating.



Yes a tankless, or a tank style water heater could be used for radiant, but it's not efficient to do so they are not approved for use with out the H stamp. There are better, and more widely excepted means to do so.



You could use a tankless to heat your domestic water, and heat your radiant floors with a heat exchanger. I mentioned this many posts ago, but I think you would need a tankless with an h stamp.



Still a tankless is more efficient than a tank style water heater, but not as efficient as a mod/con boiler for that matter probably a ci boiler.



Your hung up on the fact that your tank style WH was doing the job obviously satisfying your needs. With out knowing another level of comfort could be achieved if done correctly.



Another hang up is trying to make something work with the little available power you have.



You also have to remember that there are a lot of people that lurk on the wall, and to condone a method of hot water heating that is not of an approved method sets the stage for more people trying to do it.

SWEI

Tankless temperatures

there are two issues here.



The first is one of controls.  A tankless water heater's output temp is generally not controllable based on outdoor air temperature, which is how the overwhelming majority of modern boilers operate.  It's also the best way to deal with a high mass emitter like slab-embedded tubing.  This can be worked around with an appropriately controlled motorized mixing valve, generally accompanied by a buffer tank to prevent massive short-cycling of the heat source.



The second is one of design.  A tankless water heater's heat exchanger and burner are designed to impart a huge amount of BTUs into cold water as quickly as possible.  It throttles back to maintain the designed output temperature, generally within about 5ºF or so of setpoint.  A modern hydronic boiler is designed to maintain a body of water within a degree or two of the target temperature, even if the incoming water is only 5ºF cooler than that number.



So yes, if you manually adjust the tankless temp depending on the weather, and fire it just when necessary, it will probably get the job done.  But automating that and making it safe will cost more than buying a tool that's designed for the task.  The Lochinvar Cadet CDN040 should be a perfect fit for your house (and costs about 30% less than the other candidates having low minimum firing rates.

morpho

Hi Gordy...

I wasn't saying that the tankless set up as I mentioned was proper or efficient or safe or to code. I was just wondering why 100º water from the tankless is different than the same water from my DHW tank? Why do you need to put all the other bits of equipment into the system if the floor needs 100º water and a tankless can give you 100º water.?



Doing it right, or at least as right as it can be given the parameters I have to work within is my goal as well. The codes?…I have spent the better part of 3 weeks trying to pull any info from the folks who are the keepers of the codes. I get passed around and told things like: "it will be up to the inspector to decide what is permitted" When I ask the inspector whats needed, I either get no response or I get some vague response.



One of the main concerns about the HWT (actually the only actual concern mentioned)...be it dual purpose certified or not…is that the tank will fail. But there seems to be a concern that a boiler will fail as well in my case and probably sooner than a HWT would.

I could go out and get an certified, stamped, permitted boiler and it is just as unsafe or as likely to fail as the HWT or tankless in the end.

So that means to me a boiler is not doing it the right way….for this specific situation, or maybe it is…I get all sorts of suggestions on what to do here. I know the suggestion from the code guy in my provincial government was to just put a tap on a dual purpose HWT that I will never use.



So what am I to make of the whole thing when the keepers of the code who are supposed to be looking out for the safety of the citizens of this place are telling me how to circumvent their obvious stupid rule about having to use the certified HWT as a dual use only.



I am just trying to find a solution to my needs.



I have said it before and I'll say it again, I would love to have a cool looking little wall hung boiler making my life super duper comfy. But I keep getting the impression that it will fail, and at those kind of prices no amount of efficiency rating can make up for having to keep replacing a boiler just because it is the "correct" thing to be using.



Yes there are ways to get around this issue, at great cost and complication. A large buffer tank is one that gets mentioned. But I am right back to having …for all intents and purposes a HWT….the fire just happens to be outside the tank in another unit.



So I get confused about what to do….



I tried several times to hire professional plumbers to design and instal, but from what I have read here about proper sizing…I'm better off doing it myself…because they were out to lunch! Probably just unfamiliar with loads this small or boilers in general…who knows?



At this stage I am literally thinking about just opening up a window all winter so I can get a boiler and not have it short cycle to death.



???? whatever.

morpho

SWEI

Ohhhh…that makes sense….I think.



Any idea where I can find the price of a cadet online?

I asked the plumber to spec it in his quote, but he said he won't do Loch as he finds them problematic….and he wanted to put a really large boiler in anyway. I tried to call the dealer, but I am not an installer/plumber or gas fitter, so they won't tell me the price.

And power consumption being an issue of mine, I tried calling Loch to get the specs on power use and they had no idea.

I sent an e-mail and got no response.



So as usual I'm out in the cold…ha! …see what I did there?!? "out in the cold"….I'd laugh but its just about to be true. The passive gain can only do so much and real winter is coming!

Eastman

ODR

In Morpho's specific circumstance, I can't see where an ODR at the tankless heat source would be necessary.  If the heat exchanger for the slab is sized appropriately, there would be little advantage to lowering the DHW setpoint below the typical 120's.



Of course, the heating system supply after the heat exchanger should have ODR.



 

morpho

ODR?

What is this ODR you speak of?

Eastman

Outdoor Reset Control

An ODR enabled system checks the air temperature outside, and resets the heating system supply water target setpoint based on a simple user adjustable function.



In a nutshell, such a system delivers hotter water to the heating system, the colder it gets outside.  This helps prevent slabs and other systems from overshooting/undershooting the desired indoor air/slab temperature and increases efficiency.

morpho

A bit of perspective

Comfort is relative…spent two years in this:

morpho

Gotcha!

Thanks.

Eastman

Mabey you should...

be focusing your efforts on a wood based heat source for the floor.  It seems you certainly have the DIY skills to pull it off.



As a point of reference, if one needed an average of 30,000 btu's per day for 180 days, that comes out to 5.4 million btu's (per season), or about 1 cord of wood if utilized at an average efficiancy of roughly 30%.  30k btus can be stored in 40 gallons of water with about a 100 degree temperature swing.

morpho

And over all

It was pretty comfortable.

Armand_Colorado

PWM pump control

There are thermostats that are somewhat useful for this. Earlier, I was saying how you can use the pump to control the heat delivery from your storage. This type of thermostat uses differential and pulse width modulation to avoid overheating your house. It is not a replacement for outdoor reset, but I'm not sure you need that anyway. The one I have was about $50 (Wirsbo WT 1). I'm not sure how much my opinion is worth though, since, according to Gordy:

1. My systems are "wrong" and have not been safe, efficient, reliable, comfortable, approved and economical, despite my experience to the contrary.

2. I am a troll, "lurking" on the wall

morpho

!

Bet you didn't know there were Hillbillies in Canada.

Eastman

To be clear,

this device does not throttle the pump up and down, it does not have such a capability.  It cycles the pump on and off, and the heat source must also cycle on and off, and the heat load should be capable of absorbing the minimum output from said heat source. 



Small loads are typically handled with something like a Taco XMB-1 mixing block connected to a DHW tank.  In such a setup, the pumps can cycle frequently, deliveing precise temperature regulation, with or without ODR, and yet the tank heat source can cycle independently with its inherent buffer.

archibald tuttle

SWEI, what is cost of mixing valve as opposed to relay

probably mixing valve is a better idea from point of view of for an atmospheric gas water heater with a non-electric safety, and would slightly lessen the extent of cooler water return which could contribute modestly to tank life.



but considering that the tank in DHW service can be subject to 40 degree water entry, if you got a heater with electric ignition/control/either spark or hot surface you'd have a circuit you could control with a relay (say 501exp, hooked up to a PC-700 just to quote the TACO version but there are TEKMAR solutions too). Ditto although the relay would have to be a little more robust for electric hot water heater.



Maybe that would set you back about the same amount as the mixing valve and if you are going entry level on the hot water heater you won't get electric ignition anyway so this could be beside the point.  just wondering if you have thought about that adaptation.



I'm sure they have got the mixing valves better and more cost effective, but back when i was doing floor radiant before it was popular - carelessly revealing age -- those mixing solutions were really expensive and flukey and i have stayed away from them ever since, partly favoring the isolation of an indirect tank limiting the issues of oxygen permeable piping -- polyb[ea]utiful in those days for corrosion at the heat source and allowing for higher temps at heat source vs. floor.  of course the other downside is if you used a plate heater in this setup where he doesn't really have a lot of utilities space for an indirect and where the cost of indirect starts to push you towards entry level  or used mod-con -- you can get old munchkins for only a little more than they charge at dunkin donuts.



brian

archibald tuttle

i like [takag]ike

not all puns are perfect and mine always fall flat.  but i've got two of the original juniors in service and i think they are fabulous.  in your circumstance the stack convertiblity means you can vent in your chimney, which, if i recall is you present approach.



these are mod, but not mod-con so they don't have the true efficiency of condensing exhaust. but my experience with the first gen in DHW service has been nothing short of phenomenal. i'm sure there may be some exceptions out there, so don't take my word alone.



in the brochure you linked, i don't see the heating suitability phrasing.  maybe i missed it.  other response here point out it would work suitably, but that is different from certification.



if this is all about getting certiified to satisfy the propane company, how about getting 6 dozen 100 lbs cylinders and bringing your own propane out there. if you find a good supplier you might get better price for buying volume even though you aren't a regular delivery customer. Would guess that you would need two or three manifolded anyway, if they were outdoors, to get reliable delivery in the cold.  the delivery folks would have sized the tank they placed relative to that demand and probably you would need a larger tank to obtain the required evaporation than to service your actual consumption. that is instinct.  i haven't run the numbers.



brian



brian