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

morpho

Hey everyone,

I am not going to get into the battle about DHW tanks as radiant floor heat sources as I am sure it gets folks all fired up! (though I could rage for hours about this topic)



The "MAN" says it has to go, so I am in the market for some knowledge.

Here are specifics of my system/situation:



I have a 900sq foot slab on grade, passive solar, well insulated single story structure.

The heat loss calculations I have done put me at about 28000 to 32000 btu design loss. (depending on which calculator I punch my specifics into...long form ones not the 5 question ones) But none of these take into account the solar gain.



The pex is on 10-12" centres...sitting a bit low in the concrete I suspect.



Four loops in a single zone. (the house is more open concept cottage than "house").



Closed system.



The current illegal heater is a 40 gallon, 30000 BTU run of the mill mid level DHW tank.

(a bit under powered, but does the job)



It gets well cold here. -22ºF is not all that uncommon.



The current system fires up in the winter on average 2 times in a 24 hr period. Three if we are hitting those super cold days. Mostly at night and early morning and only runs for about 20 minutes before it hits the set point and shuts off. I don't hear from it for another 7-8 hours.



The water in the tank - once it has sort of settled out - leaves the tank at about 100ºF and returns at about 82ºF.



Overall...not knowing much about the hows and why's of this stuff...I have been pretty happy.



BUT...I need a boiler apparently.



So I need some help with a logical choice.



Space is a major problem.



Power is a MAJOR issue. (off grid solar) Currently a single grudfos runs the whole thing. And in the dead of winter I cringe when the pump is going as I know it is eating up the power in the batteries.



I don't want to oversize this thing, but I sure don't want to find I have undersized it.



Okay, let er' rip!



Thanks everyone and anyone for your input as it is getting cold and I need to pull the trigger on this asap.

SWEI

Taking into account

the solar gain will help with the overall annual heat load, but it's the "coldest day" on which you need almost 100% supplementary heat that matters as far as boiler sizing.  Some questions:



Where is the cottage located?



Given that you are off the electrical grid, I'm guessing this is probably an LPG water heater, but please correct me if that is not the case.  Were/are you using it for domestic hot water as well as space heat?



30,000 BTUs will require 4-6 GPM of flow depending on the ∆T across the slab.  900 feet of tubing in four loops would make for about 7.5' of head with a 10F ∆T or about 3.5' with a 15F differential.  I'd suggest a B&G ecocirc e3-6 Vario (the bigger one, also sold as a Laing E3 Vario) which will use about 10W to pump that.  If you're concerned about inverter parasitic losses, Laing makes DC variants but I don't have specific model numbers handy for those.

morpho

calculation update

Hey SWEI,

Thanks for the input.



http://www.builditsolar.com/References/Calculators/HeatLoss/HeatLoss.htm

I just did this heat loss calc and came up with a design loss of 17310 btu/hr... (though I'm not sure how much faith I have in that number...but I don't know how the physics work anyway) so round that up a bit because...well...because reality might be a bit less efficient...but not much.





I am located west of Edmonton Canada...more or less 10000 heating degree days.

Yes LPG...sorry...should have mentioned that.

I have an existing Tankless unit for domestic water, but I would be open to a combo unit so I had options if the tankless craps out.



I have limited water. No well, just a 1000 gallon cistern full of rain water. So I can't waste a drop

morpho

the calculation for my place

pdf of the calculation

morpho

pex run lengths

I dug up the pex loop numbers I wrote down on a scrap of paper and the loops I layed down have a max length difference of 14' The shortest is 222' the longest at 236'

SWEI

236 feet of 1/2" PEX flowing 1 GPM

would be about 8.2 feet of head with 100F water.  Too much for an ecocirc, but a perfect fit for a Taco HEC-2 (Bumble Bee -- curve #3 shows 32W needed for that flow.)  A Lochinvar CDL040 would work and has a 9k minimum firing rate, but pretty much requires primary-secondary piping (needs a separate pump on the boiler, but the baby ecocirc can handle that.)  The WHL-055 could handle it with a single pump, has an 11k minimum firing rate, but costs about 30% more than the Cadet.  Viessmann 200-W B2HA 19 is another option with a 12k minimum firing rate.

morpho

ahhh...now I need to learn more stuff

Thanks for the info SWEI,

I am putting together a folder with all these products in it....looks like engineering porn.



I gather I need to get a handle on the concept of "head" as it pertains to heating and pumps. I will find a link on the internet I am sure...though the search engine may take me to a few odd places first.



Am I correct in observing that head relates to the longest run of pex in a zone and not the total combined loops in that zone? (I have one zone with three loops)



regarding Boiler sizing:

I haven't found it said implicitly, but is the idea to take your calculated design load loss and match as closely as possible to this? (this being the worst case scenario day you are likey to have to heat in...most days being much less. Because if this is the case I am thinking that for much of the time I will be barely scratching the surface of the power any boiler I get.

SWEI

head loss

is a measure of pipe friction.  For any given pipe diameter, head loss is a function of developed length (look that one up) and flow (GPM.)  In a parallel circuit, the pump has to produce sufficient head to push water through the longest branch, but flow enough to fill all the branches.  The differential equations that describe all this are a bit complex, but there is plenty of software (some of it free) that can do the work.



Download and read a few of the PDFs from here (probably starting with #12) and you'll learn a LOT http://www.caleffi.us/caleffi/en_US/Site/Technical_library/Idraulica_magazine/index.sdo

morpho

thanks for the link

Ahhhh...pretty basic....as long as you don't dig too deep into the specifics that is.

Thanks.



What kind of efficiency should I expect from one of these Mod con units if I am typically at the lower end of its power?



Would I expect to see the LP consumption go down or up when compared to my DHW tank that I use for heating?

Keeping in mind that my water tank was running twice a day for 20 minutes each time and this kept the house warm. Not to say it was efficient, but it was effective. I read others saying their boilers are running for hours everyday. I would freak out if thats what I am looking forward to.

Gordy

Water heater efficiencies

As a heat source if it was a run of the mill basic one about 65% efficient maybe.

In a nut shell you should see improvement. The hurdle lies in your electrical consumption.



Whatcha using to harness the power? Wind, PV ?

morpho

good point.

WOW,

It's the you "should" see improvement part that concerns me.



2, 3, 4 thousand for a boiler and I "should" see an improvement.

What is all that money for then?!? To make warm water?...I was doing that for 400 bucks! I have a bad feeling about this. If I don't get the right unit this will go sideways quickly.



So, the Power is PV (solar) and If the boiler runs about as often as the water tank did/does it's not a big issue really. But if the boiler runs all the time for whatever reason it just won't work. IS there any reason the boiler would run significantly more than the hot water tank does?



The info about all these boilers doesn't even mention the standby losses from all the fancy pants computers in them.



Okay, thanks for the further insights.....

Zman

Options

It sounds like your real world heat loss is less than 5K BTU. Your 30K water heater is putting out about 20K and is running infrequently.

I share your concern about the mod/cons electricity use. The fan itself is using quite a bit more than your existing unit then there is the standby loss.

Theoretically a micro CHP sounds good. It does not make much sense if you don't need the extra electricity.

Maybe a conventional cast iron boiler?

You could use a DC powered relay to cut all power to the heat system when there is no demand.

I am curious as to how they made you change your system. Did someone just send you a notice?

An interesting puzzle, keep us posted.

Carl

SWEI

Mod/con efficiency is maximized

with low return water temps while firing at low rates.  Somewhere near 98% on a good boiler.



Your design load could very well be 17-18k.  The vast majority of the time you would need only a fraction of that amount.



The electrical consumption is a real concern.  What kind of solar thermal potential do you have up there?  Evacuated tube collectors may be worth investigating.

Gordy

My statement

Was meant to imply that the mod/con will be a lot more efficient. How much depends could be 30% and up.



Problem is the low load, and gas boiler sizing available to match it. Running at low end modulation all the time is a waste of a boiler. Your load is more suited to a small electric boiler, but that's not an option. Then there is the water heater which was working then now you can't use that.



I'm curious about how the "code man " got involved also. There are condensing dual purpose water heaters Polaris by htp. They are pricey, and still have the electrical drain also.



What are the consequences of not changing out the wh, and how long do you have to rectify the violation?

Gordy

Okay

May sound a little crazy. Why not use the tankless you have with a HX loop to the existing water heater for the radiant, and call the water heater a buffer tank for the radiant. Your expense is a plate heat exchanger some pipe, and a efficient circulator in that loop.

Rich_49

Please share

with us WHY the Code official states that it must go . There is a possibility that with some documentation and design on paper by a qualified person it may not have to . Codes and documentation in Canada are very technical .



http://www.healthyheating.com/Do-I-need-an-engineer.htm#.UlaEor7D_5o

morpho

yes I am crazy

"Interesting puzzle"

I have a whole whack of expletives that better reflect my feelings on the issue...but I am sure a moderator would redact my colourful words.



Gordy,

You scarred the begeesus out of me. If I was not likely to see an increase in operating cost, I would think the whole boiler industry needs to have a long hard look at itself.

The tankless can't be approved either as they are not stamped for space heating use...no amount of buffer tanks or exchangers will make the code guy happy.



The way this has come about is this:



I moved out to a piece of bare land a few years ago with the stellar plan to build myself a home. I arrived with a coffee can full of rusty nails, a hammer, saw, screw driver, a car, and a 45 year old 12' travel trailer. I got for $100. No heat, no power, no nothing.



I bumbled around the permit process a for a bit and got delayed with that, the plans the permit folks needed were delayed from the "Designer". I ended up having to walk away from that plan because fall arrived and I was no further than I had dug the foundation out.

So I moved the trailer to a sheltered spot, built a 20'x20' sort of timber frame around it, pulled a 1000 gallon water tank inside, wrapped the whole thing in vapour barrier, encased the whole thing from top to bottom in straw bales, (except for the south face, which I closed in using greenhouse polycarbonate panels for solar heat gain) I covered the structure with two industrial tarps, built myself a rocket mass heater inside the shelter, and settled in for a lovely Canadian winter. I pulled apart an old beaver dam about a mile away and humped backpacks full of that to burn in the Rocket mass heater.

Worked like a charm the whole thing did! It could be -28ºF outside and if the sun was shining I was wearing shorts inside. The wood heater didn't even have to be fired up until the evening.



So spring came and I did my own drawings, submitted them and started to build the cottage. I did everything by myself except for the concrete. Having never even built a bird house before...it went okay actually...just a slow process...Fall came around and I was just about closed in...just waiting on the delayed windows to arrive. Snow arrives still no windows. They finally arrive and the driver steps into the back of the truck and unhooks the strap on the 16' triple glaze patio slider and I watch it topple over and almost kill the driver. I had to wait another 5 months for that unit to be replaced. So needless to say I spent another winter in what I was now calling the "refugee camp". I was expecting the UN to airdrop food and blankets at any moment.



So long story short...I get to the plumbing and gas fitting stuff and I talk with a few plumbers and they tell me after looking at what I am up to that a DHW tank will fit best in this scenario. Not ideal, but will probably be better than a boiler....(didn't understand the why's and how's at the time, but I took em at face value) I look it up and sure as heck people all over the place use a hot water tank for this. Cool this is what I do then. Finish all the gas work etc. Pressure test it....works great...hmmm? I decide to throw a 20 lb LP tank on it and see how it works...winter is here after all...Works great! The floor heated up, the gas range worked the tankless unit made hot water to shower in. (after two years with no running water you have no idea what a shower meant to me)

So I get going on other house things. This brings me to today. I decide that I had better get this inspected and approved so I can get the big LP tank put in the yard and stop WAY over paying for gas. The inspector says to me that this kind of set-up is no longer approved and I will need a boiler or a indirect hot water tank rated for both space and domestic water heating.



And fair enough...if these are the rules...it's not their fault..I'm the guy who did this....I may not understand the rules, but they seem pretty inflexible about the whole thing.



So now I am trying to figure out how to make this work and still make them happy and not put myself into the position where my system no longer works (because it has been working great thus far!) just to satisfy the code.



interesting times for sure.

Zman

Options

Option 1

Purchase a mod/con boiler with controls that are low in power consumption and will run off inverter power. Triangle tube trimax boilers would work well. This option is expensive and will use more electricity than you would like. It will save on propane but you may have to add solar.



Option 2

Buy an inexpensive cast iron boiler that is around 80% efficient. This is less expensive than option 1 and will save propane as compared to your existing setup. You could wire it so it will be completely powered off when not in use. You could likely use your existing vent. It would use a little more power than what you have now, but not much as it does not have a forced draft.



Option 3

Fool your inspector. Temporarily remove your existing heater and replace it with the cheapest approved heat source you can find. A used furnace or freestanding stove would be a good choice. After you get your inspection, the water heater would magically reappear and you would be a happy camper. Not exactly the most honorable approach, "The man" has not left you many options.



I think this is the only instance I have heard off where a hot water heater makes sense as a radiant heat source.



Carl

Gordy

Interesting

There are low load instances where water heaters in the right method are feasible.



Mans carbon foot print is minimal, and he is penalized for it in a way. By being forced into a method that uses more energy than he already does.



And I'm not so sure the ROI is there for an oversized conventional, or mod/con boiler swap being that there is not one small enough out there in his load ban. Sure a WH is not efficient, but is an oversized boiler?



Basically you need a heat source with an ASME stamp to get approval.,



So have you entertained the idea of a wood boiler? Is it approved in your areas?



Do you have the wood available on your parcel to supply it? Along with the ambition?

Rich_49

Water Heaters

There are a few manufactured that are approved for space heating . AO Smith vertex is 1 that jumps to minds . 76000 BTUh , HX and 2 pumps . Probably the least expensive , unintensive labor option . Then you will have an approved unit made to do both jobs .  You sound very self reliant which is a good thing , it is too bad that Johnny Government always has to retard innovation and alternate methods . Of course there are other than AO Smith that is just the first unit that I think of .

Eastman

a bit under powered

"(a bit under powered, but does the job)"  Why did you think the 30k heat source was a bit underpowered?  Does it lag changes in weather?  House never gets fully up to temperature? Or 20 min is too long to be running the pump?

Gordy

Eastman

I'm willing to bet that this scenario is outside the normal comfort creation of a designed radiant system.



The water heater all though doing the job (to what setpoint?) is probably playing catch up mostly during its on periods. We don't know what it is set at either.



Also a 30000 btu input water heater is probably only maybe 21000 output.



A ECM circ would help his present set up with the power consumption. All though the water heater must go.

Eastman

I wonder what is really the thermal buffer here.

Is the 40 gallons of extra water justifying the space it's taking up?  I'm thinking the instant water heater could fire directly into the slab via the plate heat exchanger. 

Rich_49

I beleive

the problem may be with documentation of the system gentlemen . Canada had the same problems with bad design that we have and at present all jobs must be engineered / designed / approved and I mean if you install a different circ than what is on the plan , YOU FAIL , Period . Not sure this is what is happening but Canada embraces innovation as long as it can be shown to be sufficient . there must be some issue with the install .

Gordy

I'm sure it is Rich

And thats why my post on using the tankless with an hx wont fly either.

Gordy

Buffer

May give him some wiggle room on when he uses his circs. Being he is strapped for power.

jumper

forgive me but

You said you don't want to go into it but I'm curious why you mustn't use a water heater for heating?

morpho

I'm back....

Sorry for the vanishing act, I went to the city and painted my moms house. Please remember anything I say is tainted by paint fumes.



ZMAN:



The mod con sounds great for space..it would clean up the utility room a bunch.

The cast iron boiler could be the option I have to go with..though I dont know what the logical way to cool the water down for the floor is.

There is no fooling the inspector...well probably is, but I don't have that much energy. My goal isn't to "stick it to the man" I just want to get an LP hookup.



Gordy:

I have given some thought to a wood boiler, but I would like/need the option to go away for a week or two. Not likely if I have to feed the boiler. Though I do like fire...hmmm.



Rich,

I will look into the HW tanks a bit more...thanks. Maybe this is a solution...My best guess will be that I won't be able to use it as a stand alone and will be forced to plumb a fixture for DHW off of it as well as the heating to make the code guy happy (I have a tankless that I really like)



Eastman:

Sorry, should have qualified that a bit.

I think the recovery rate on the water heater is a bit under what it could be. The temp drops down a few degrees lower than I would like it to be. But this is not based on any kind of engineering or actual knowledge...just gut feeling.



Gordy:

The set point is 22ºC...so 71ºF -ish and yes I feel the tank is "playing catch up"

Though from what I keep reading about the boiler set-ups, they are not without their problems dealing with a task they are not really designed to do. (heating a slab...otherwise there wouldn't be all these primary/seconday...close t's...add cold water...add warm water...mixing valves....etc..... add ons to make it work) Though I am confident I know less than nothing about how it works.



Jumper:

Why can't I use a water heater...I have yet to get a really really good answer.

An notable engineer involved with radiant heating in the US was cool enough to respond to an an e-mail a few weeks back when I asked what the danger is and he said he doesn't support DHW tanks because he has seen a couple of installations where the low temps created condensation and rusted out the tank.



I am not saying he is wrong...like I have said I am not an expert in any way shape or form....but I keep coming across all sorts of issues with boilers creating all sorts of chaos in slabs due to too much heat, not enough heat....condensation rusting out the guts....thermal shock....etc.







Everyone:

I don't know whats what anymore.

If you where me and you had to get rid of the DHW tank...what would you get?

As in what unit? how would you plumb it?

Why?



Thanks

Eastman

How exactly is the current system set up?

22 C is the setting on a regular air thermostat, right?  What is the thermostat connected to?  --the pump?  The pump runs and eventually the tank heater fires up?

Gordy

Zmans cast iron option

I don't know what products you have available in your area. Thinking parts if ever are needed.



But ci boilers properly set up last for decades. You would mix down your supply temps with a valve that mixes cooler return water with the supply water.





I'm assuming that this install must be done by a certified pro in the industry?



You will not find the perfect match to your load with any boiler out there, gas fired that is. All though a mod/con will get close save more fuel, problem is you would never use the smallest ones full potential, but that would apply to the smallest ci boiler out there also. The ci boiler would fire at full output always where a mod/con can throttle down.





So what I see it boiling down to is how much you have to spend. Because either boiler type will get you there. Fuel will never get cheaper either.

morpho

some pictures

Eastman:

The pump is triggered by a thermistor in the slab...(in a sleeve that is in the slab)

I have the slab temp set to 71ºF.

When the slab drops below that, the relay fires up the pump until the set point is reached. Pretty simple.



Gordy:

The boilers available in the area are from what I can find:

http://www.aosmith.com/

http://alliedboilers.com/

http://ibcboiler.com/

http://www.laars.com/

http://www.lochinvar.com/

http://www.nythermal.com/

http://www.viessmann.ca/

http://www.weil-mclain.com/en/weil-mclain/

http://htproducts.com/

and probably a few others if I poke my nose around.



Do I need need a certified installer?...?...?

Don't know...I pulled the permit for al this and as the home owner I am allowed to do that. Will the manufacturer honour warrenty? Will I install it correctly? (though in all the things I have done with this house the gas and plumbing were without a doubt the easiest....sorry gasfitter guys...but it was really simple. I spent weeks agonizing over the how's and why's of how the gas should be done and in the end it was a matter of putting pipe dope on the threads and tightening it all together then making sure it doesn't leak.

(yes I know it is WAY more complicated when you get into more complex systems...but getting propane to a range and a water tank was dead easy.) Try moving trusses, swinging them into place and securing them as a one man operation..now that was tough!



Here are some images to give you a visual of what I did...not saying this is right, correct or logical...it's just what I did.

morpho

pictures

Some images

Eastman

how about a two stage boiler?

Loch has their copper tube units with stage 1 starting at 23k btus.  Looks like it might be a drop in replacement for the water heater.



I can't find any two stage cast iron boilers in this size range.

RobG

What about this

How about using the smallest cast iron boiler available and an electric water heater as a buffer tank? You might be able to find the electric water heater and maybe even a boiler on Craigslist. Just a thought.

Rob

Gordy

Rob

My question would be if an electric water heater as a buffer tank is legal?

morpho

I can pretty much guarantee I don't have the power

Hey RobG

I doubt that my solar panels..or more accurately the batteries...could power a high resistance load like an electric water heater for long anyway.

My little grundfos pump is my highest single load in the house at a max of 87 watts!

If I turn on all my LED lights in my house the load barely breaks 120watts.

I have no idea what an electric tank uses up...but a typical hairdryer is 1800 watts....needless to say my wife doesn't have one of those.





Not to mention I am still at a loss as to how the boiler is any better than a DHW tank when I keep seeing the boiler hooked up to a water tank....why not just have the hot water tank?

Clearly a boiler is not really designed for in-floor heat. Otherwise all this stuff wouldn't be needed.

Is there any installation where there is just a mod con hooked into a closed loop with one pump? Everything I see involves buffer tanks or heat exchangers etc. etc.

At this stage my ignorance of how this all works is obvious. I am so confused!

My DHW tank set-up is so simple



As a side note I was reading the specs on a Viessmann modcon and the "frost protection" function comes on when the outdoor temp gets down to one degree above freezing and shuts off when when it comes up three degrees above freezing. Uh...that is 7 months around here. I could burn polar bears and the last giant redwoods and be more eco friendly than that!

Gordy

Morpho

Miss understanding..





The electric water heater would not be powered but be used as a buffer tank. Basically a vessel that holds water up to heating temp that the boiler heats up.



Rewind a couple posts when I was referring to using your tankless with a heat exchanger to a water heater(buffer tank) so the water heater would not actually heat the water but store it.



This was all in vane as in trying to use your present components into something code worthy would not work anyways after further info you provided.



You have a low load situation, and as of now boilers are not made that small not a usual circumstance in the industry, but becoming more usual with low load homes of larger sizes than yours in an effort to decrease our carbon foot print.



Yes boilers are very efficient and entirely for use in hot water heating, and domestic water heating via an indirect water heater . Your heating and making hot water with a 95% efficient appliance verses a 65% efficient water heater. Strictly speakingg of boilers in the mod/con category .



I think this thread got twisted into making what works for you, your load, and seemingly space and budget , and what you have from what is properly done in this industry



Your problem is you have a low load house with solar gain, and limited electrical output to really make what's available in size be a perfect match for what you have.



There are certain, and very few situations where a standard water heater used as a heat source applies. They lack the ASME stamp to be used as a heat source so you should not use it for that the code man is not wrong in his observation.



I should add the reason water heaters lack the proper certification for a heat source is money it costs more to certify for that than for just heating water to bath wash clothes, and dishes. So water heater companies just want to sell water heaters for that what you do with it once you buy it is not their problem.

Rich_49

I See

you have Ht Products as something that is available to you . Look at their combined heat and hot water tab and see if the Versa Flame might not fit your needs . It is a high mass (55gal) mod con boiler that does not require primary / secondary (1 pump) , I would switch out the 87 watt pump you have there and install a Taco Bumble Bee (HEC-2) . This unit also has a flat plate heat exchanger that employs a pump on the boiler side to heat DHW . Not as expensive as many of the options being discussed and you're only gonna be adding about 22 watts to your consumption . Due to the high mass you can program it so that it fires minimally conserving your fuel also .  tell me what ya think  

Eastman

20 minutes

Morpho, what is running for 20 minutes?  The pump?  The burner? Both?  Does the tank run longer than the pump, or vice versa?  Do you know the flow rate of the system with it's current pump?

morpho

took a moment

today to think straight and I think I need to stay clear of the boilers and especially the modcons...too much money, too much tech, too much power needed, no service very close....shame as the dimensions are great. Probably why I keep looking at them even though I know they are not a good fit.



Rich.....

So a hot water tank with side in/out connections seems to be the best option. I looked at the AOSMITH vertex online and it is the same width as my current tank and 20 inches taller. I will have to redo all the water and gas lines ...and venting in my place to do it. The tankless will end up on kijiji with the old hot water tank.



Does anybody have a list of tanks with side ports for space heating?...ones that you would trust?



Anybody know if I would be looking at increased fuel consumption considering the input for a unit like the vertex is 76,000btu's? Seems a tad big for my needs....and so it begins again!.....

seems to me there is a need for a smaller hot water tank specifically for in-floor radiant.

Ahhh nevermind! either way this is the option I have if I want to satisfy code.....I knew I should have moved further away from civilization!

morpho

Eastman

Sorry...being vague.

The pump runs about 20 minutes to get the slab to the set point.

The tank takes another 10 minutes or so to heat back up after the pump shuts off.