Choosing a reliable boiler

[brucewayne]

Yes, an 80-100,000 BTU/hr boiler would be complete overkill for a 1000' house, unless it has single pane glass, no wall or attic insulation and is located in Fairbanks, AK.

o assess what really makes sense it helps to know your location (got a ZIP code?), ers electric boilers would be substantially cheaper than oil. In most locations propane would be more expensive than #2 oil. Since all utility markets are local, it's important to look up the local pricing (and pricing trends) when trying to come to a decision.

What is meant by "...with my tank...........

lol i live in Canada, Ontario. Winter is very bad sometimes, -20. My boiler uses a gsw water heater storage tank, rated 35000 btu-hr, has the duct work. If i could buy the Abrams, i still wouldnt pay them 14k for the Bosch setup. Thats what my heat supplier offered, or a slant fin for 10k after tax, maybe that ones better?
another contractor offered 7k for Navien combination setup, or slightly less for 6800 and i keep the tank, errr water heater tank.

I googled these deals, seems 5k is average price for new boiler install. Or maybe Im wrong, not cheap but wrong?

 

[Dana]

Ontario is a big province with a wide range of climate (eg. Kenora is a heluva lot colder than Mississauga, and Fort Severn is colder still!). Care to narrow it down a bit? The location is necessary to be able to estimate the 99th percentile temperature bin, and the average heating season outdoor temp, both are relevant to specifying a heating system.

Wintertime low temps of -20C isn't a very severe constraint (are you on the Ontario Riviera or something?), and -20F isn't bad either. A typical 2x4 framed 1000' house that's insulated would have a design heat load between 20,000-25,000 BTU/hr @ -20F.

Do you have access to last season's gas billing (exact meter reading dates & usage numbers).

Even the smallest Navien combi (the NCB-180) has minimum firing rates are too close to your likely heat load, which means it can't modulate with heat load much, and not enough burner for really decent domestic hot water performance at your likely incoming water temperatures. Combis are rarely a good fit, they're better for houses with really big heating loads, but modest hot water needs, which is the converse of how it is with most houses.

A better solution would be a fire tube mod-con with a big turn-down ratio and a indirect fired hot water tank (or a stand-alone tank with it's own burner.) You may or may not have enough heat load to even run the smallest mod-con or combi in condensing mode without short cycling even the smallest boiler, but I suspect it would be pretty bad with a Navien combi.

How much radiator, or baseboard etc do you have?

What is the input and output BTU or wattage ratings of the current boiler?

The NTI Trinity TX51 (57K at max fire, 7.1K min- literally half the min-firing rate of the smallest Navien combi) is probably a reasonable fit for a boiler, or the Lochinvar CDN040 (40K max, 9K min). The Laars Mascot MFTHW80 fire tube boiler is 80K max, but modulates down to 8K, and should be pretty cheap. Like Navien, it's made by a first-tier Korean boiler company (Kiturami). The exact same boiler is sold in the US for about USD $1700 under the Westinghouse name plate, but Laars probably has a bigger presence in Ontario. The low pumping head of the fire tube heat exchangers and tolerance for high delta-Ts makes it a pretty cheap & easy swap out for a cast-iron boiler, since (unlike the Navien or Lochinvar) there is never a need for a hydaulic separation point (aka "primary /secondary" plumbing) - it can be pumped direct and function without a problem in 99% of the heating systems out there- practically DIY-able without a lot of hydronic design skills.

I suspect the TX51 would be fine pumped direct too, if that's somehow cheaper than the Mascot MFTHW80. Lochinvar is in the mode of voiding the warranty if it isn't plumbed primary/secondary, which adds the cost of another pump and more complexity to the installation. Navien insists on hydraulic separation too, and is happy to sell their pre-made manifold of closely spaced Tees with every boiler & combi, which is over & above the list price for the boiler itself.

Quotes for swapping out a cast iron boiler with something exactly the same size can be as cheap as $5K in my neighborhood, but it's usually a bit more. Mod-cons and condensing combis are usually closer to $10K. But swapping-in the Laars-badged 80K Kiturami (Mascot MFTHW80) should not be more expensive than a cast iron boiler, and could even be cheaper. The boiler itself isn't any more expensive than equivalent output cast iron, and the venting (being plastic) is cheaper, and even the plumbing can be simpler (no need for boiler bypass or other plumbing tricks to protect the boiler from condensing temperature water needed, since condensing temperature return water is the active goal.) The output at high fire is on the ridiculous overkill side for a house that size, but since it can modulate down to 8K-in/ 7.5K-out it's probably going to work in condensing mode even with minimal amounts of radiation to work with.

 

[Sponsor]

 

[brucewayne]

Wintertime low temps of -20C isn't a very severe constraint
Do you have access to last season's gas billing (exact meter reading dates & usage numbers).
How much radiator, or baseboard etc do you have?
What is the input and output BTU or wattage ratings of the current boiler?

Thankyou, Lars sound good then, I have their boiler, its mighty old though. Around 31 years, could be older, because I only have a hvac note printed "1985" by a local contractor who either cleaned it or installed it, doesnt say which. The heat exchanger is rusty this year. I have it cleaned 1/year by my supplier.
The max BTU 100k; theres no detail to tell what watts it uses, has 12 amp wire hooked to it. They dont make the parts for this one anymore.

I live in the gta, right in the city. There is 1 radiator per room, 6 radiators total. unfortunately all bills been thrown out, have to call directenergy on Monday for meter numbers.

Im just worried if heat exchanger cracks, I dont know how bad that is.
but any modern boiler would help, Bill is roughly $100 every winter or more, doesnt go much higher. House insulation is mediocre, not too good, not very bad though.

If you think the Lars boiler is good, Then i will give them a call. I need to replace this year. I only found out heat exchanger was rusty last week so yea.

 

[Dana]

Toronto's 99th percentile temperature bin is +1F/-17.2C, so your 99% bin probably isn't colder than about -18C (meaning, 87 hours out of an average year will be below that number.)

Cast iron gas fired boilers circa 1985 typically had a raw combustion efficiency of 80%, so your 100K input boiler has an output of about 80K. If (it's a big "if") the radiators were sized to deliver the full 80K BTU/hr of heat into the rooms with 180F/82C water (and aren't undersized for the boiler making it cycle on/off during continuous calls for heat), at condensing water temperatures (130F/54C output or lower) the radiation would be able to deliver about 40K. That is probably still way more heat than it takes to keep the place warm at -18C, which means you can probably set up temperature on the boiler to run in condensing mode 100% of the time, and to modulate it's firing rate with outdoor temperature to deliver super-efficient nearly continuous burns, as opposed to cycling on/off multiple times per hour dozens of times per day. The lower the system temperature the higher the combustion efficiency. A high burn-time ratio with fewer ignition cycles is also good for efficiency.

If you measure up each radiator you would be able to come up with the "Equivalent Direct Radiation" (EDR) of each, and add them up to get a better handle on the BTU output at any average water temperature. Use this document as a guide. With that information we could make reasonable estimates of the water temp at which the 80K Laars Mascot would begin cycling on/off. It's probably well into the condensing temperature, but with the total EDR number we'd know for sure what to expect.

If you can get the exact meter reading dates & amounts over a winter period we would be able to predict the heat load well enough to come up with an appropriate set of temperatures as a starting point for tweaking in the "outdoor reset" curve. You can read up on how to program the reset curve beginning on page 64 of the manual.

 

[brucewayne]

sorry couldnt get back on forums was busy this week, i totally forgot. But anyway, i tried what you said. Could i get help to check if my edr calculations are right?

for example, my house roughly 1000 square feet. Basement has no radiator though, so id try 700 sq feet

radiator is hot water based, thus
170 BTU/hr * 700 = 119,000


but i dont know how to count the tubes in a column radiator. This one has 6 sections single column, 4 feet. I cant calculate any further, let me illustrate.

 

[Dana]

Where does the 170 BTU/hr per square foot of conditioned space number come from? Your heat load to conditioned space numbers are likely to be roughly 1/10th that much (with the doors and windows closed, anyway... )

The 170 BTU/hr number is for the square feet of the radiator surface, not the floor area, but more accurately the "equivalent direct radiation" (EDR) square feet of the radiator, not the size of the house. The EDR is the characterizing the size of the heat output as if the shape of the radiator was nothing but a flat panel. But since it it's a flat panel, but rather a complex shape, it's heat output is a function of more than just it's raw surface area. When the surface is broken up into sections with air between them, and with tubes in each section where air can flow between the tubes or columns, the air convection generated by those heated air spaces transfers heat faster to the room air than a blank flat panel the size of the actual surface area of the radiator. For more than a century the heating characteristics of radiators have been described in terms of EDR, to be able to do apples-to-apples comparisons of radiators of different sizes and shapes. The radiator heating capacity guide shows you how to measure the radiator to estimate the EDR square feet of the radiator.

You have a six section radiator, but you haven't measured it's height, or the depth of each section. Without an end-view I can't say with 100% certainty if is a tube type or a column type, but I'm guessing it's a column type (one, two, or three or even five fairly wide ovaled tubes, not a series of narrower tubes.) If you can find radiator spec of similar dimensions to your in some vendor's catalog it will probably be pretty similar. They usually specify them in square feet per section, which is the EDR square feet, not the actual surface area. From the side view appearance yours is probably a column type radiator with three columns(?). It's really hard to tell from a side view only and with no dimensions.

There are column radiators with just one column, but they're usually nowhere as deep /wide as yours seems to be.

^ this is a column type radiator with two columns^

^this is a tube type radiator, with five tubes^

Add up the EDR, don't bother calculating the 170 BTU/hr output, which is only it's output when the average water temperature is 180F. If you look at the nomograph in the sizing manual you'll see it's pretty much a straight line. At 130F average water temp (the high end of the condensing range) the output would be about 70 BTU/hr per square foot EDR, not 170 BTU/hr.

 

[brucewayne]

ty, its definitely 2 column. I measured one radiator just now
please tell me if the math is right.

Height is 32". Should i also add height from the four legs?
anyway heres the math,
32" in 2 column = 3.33 * 6 sections = 19.98 EDR ?



Also i found out how much energy used, hope its not a problem, utility only lists in
my max gas consumption was 487 m cubed. With no average, lowest was 264 in January 2015.

 

[Dana]

You measure the height from the floor to the very top.

If yours is pretty typical in depth ( ~8"wide give or take) your calculation will be about right. The end sections with legs don't change it much, and is never specified separately.

Yours is a bit unusual with the side-by side plumbing ports on one end instead of one pipe connection on each end, which may skew it a bit- how wide is each section?

Assuming it's about 20 square feet EDR, it should be able to deliver between 1,000-1,400 BTU/hr at decent condensing temperatures

The exact meter reading dates and a postal code would be necessary to calculate the load from fuel use, using temperature data from the nearest weather station on the period between meter readings.

There is about 37,500-38,000 BTUs of energy in a cubic meter of natural gas. It varies a bit with the exact mixture of natural gas, but this type of calculation can tolerate that much error.

 

[brucewayne]

Nice so my math is right. I didnt always sit in the front of my math class, but sometimes i got an A.

Well the sections are 7 " wide. Will that change the formula up?

i dont think need that much precise for btu? but i have coordinates via google earth. they are within my neighbourhood. Id rather not say my address basically but anyway,
here it is
43(circle)-42'- 21.75" N 79(circle)-24'39'.91 W

 

[Dana]

At 7" of depth it's a pretty standard column radiator, so you can use the 3.33 square feet EDR number. Calculate the total square feet of all radiators in the house.

With some exact wintertime meter reading dates (not the billing dates) and cubic meters used between those dates we would be able to establish reasonable bounds on what the realistic heat load numbers are.

 

[brucewayne]

i had some contractor visits, not pleased with what was offered. i keep getting 80k-100k btu offer. i dont know what to do.

i sized all radiators already.
total btu required was roughly 30k. I had one lowered to 50k after i explained to the contractor about sizing radiators.

anyway, could please double check my math? especially 5) since i have tubed radiator also.
________________________Height___________________________
1) 2 column 5 section------------ 36"------------ 16.65 *170 = 2830 BTU
2) 2 column 8 section------------ 36"------------ 26.64 *170 = 4528 BTU
3) 2 column 6 section------------ 32"------------ 19.98*170 = 3396
4) 2 column 4 section------------ 36".----------- 13.32* 170 = 2264
5) 4 Tubed, 10 section-------- 36"----------- 42.5*170 = 7225
6) 6 Tubed, 14 section------------ 25"------------ 56*170 = 9520
____________________________________ Total = 30k

im not sure why you mentioned 1000-1400 btu expected at decent condensing rate?
so should i expect half return from boiler to radiator?

thus if i get 80k, it would deliver 40k btu on decent condensing rate? its never perfect i guess.

 

[Dana]

i had some contractor visits, not pleased with what was offered. i keep getting 80k-100k btu offer. i dont know what to do.

i sized all radiators already.
total btu required was roughly 30k. I had one lowered to 50k after i explained to the contractor about sizing radiators.

anyway, could please double check my math? especially 5) since i have tubed radiator also.
________________________Height___________________________
1) 2 column 5 section------------ 36"------------ 16.65 *170 = 2830 BTU
2) 2 column 8 section------------ 36"------------ 26.64 *170 = 4528 BTU
3) 2 column 6 section------------ 32"------------ 19.98*170 = 3396
4) 2 column 4 section------------ 36".----------- 13.32* 170 = 2264
5) 4 Tubed, 10 section-------- 36"----------- 42.5*170 = 7225
6) 6 Tubed, 14 section------------ 25"------------ 56*170 = 9520
____________________________________ Total = 30k

im not sure why you mentioned 1000-1400 btu expected at decent condensing rate?
so should i expect half return from boiler to radiator?

thus if i get 80k, it would deliver 40k btu on decent condensing rate? its never perfect i guess.

The 1000-1400 BTU/hr for a 20 square foot radiator is an indication of what it will deliver in the condensing range. With lower boiler temperatures the radiators can deliver even less, and at higher temperatures they deliver more. At 120F average water temp, the return water is cool enough to get combustion efficiency into the mid-90s, but it delivers only 50 BTU/hr per square foot EDR. (20 square feet x 50 BTU/hr = 1000 BTU/hr.) At 130F average water temp the return water temp will warmer, at the edge of the condensing range, and combustion efficiency will be in the very low 90s, but the radiators will be emitting about 70 BTU per square foot (20 x 70 =1400 BTU/hr).

Only at 180F average water temperature is the multiplier 170 BTU/hr per square foot EDR. The fact that your radiator size indicates it wouldn't deliver more than 30K even at typical cast-iron boiler temps means that you don't really need a boiler with more than 30K of output. But with a modulating boiler that can back off the firing rate to something well below 30K, you have options.

At output temps over 140F (really meaning at return water temps over 125F entering the boiler) it won't condense at all, and only deliver ~87% efficiency but it looks like you have about 175 square feet EDR. That is enough radiator that it can still deliver 9,000 BTU/hr with the boiler well into the condensing temperature range operating in the mid or even high 90s for efficiency, and at least 12,000 BTU/hr at combustion efficiency greater than 90%.

The minimum firing rate of the Laars Mascot MFTHW80 is 8000BTU/hr (input), and at 95% efficiency it's output would then be about 7600 BTU/hr. With 175' of radiator to work with that's 7600/175= 43 BTU per square foot, so as long as the average water temp is ~117F or higher it can run continuously, without cycling the boiler AT ALL during an extended call for heat, which is great! The Bosch or Navien combi would be cycling on/off at any condensing temperature, since it's minimum output is higher than what the radiators can deliver at those low temps, though the thermal mass of the water volume + iron would be enough to save it from abusive short-cycling. The Navien NHB 80 boiler (not a combi) could do it without cycling though, but it's heat exchanger isn't as amenable to the flow you're probably looking at for the radiators, and it would necessarily need a second pump and a hydraulic separator, whereas the Laars can be pumped direct in almost any system your size.

Even at 200F rads only put out about 200 BTU/hr per square foot EDR. So, at 175 feet of radiation you're looking at 35K of heat emitter @ 200F. That means any cast iron boiler that puts out more than 35,000 BTU/hr would be oversized for the radiation.

 

[brucewayne]

Wow, im suprised my boiler lasted this long. Its 100k and 80k depending if using different gas.
shouldnt it have stopped running by now? i assume it would have short cycled to the scrapyard already.

i dont know if i should have read the article better, that makes perfect sense, Could i determine average temperature of water?

then i could have exact BTU known, or does that really matter anyway.


if 170 F is good enough, im fine with that. Otherwise, id like to recalculate with exact water temperature, unless that depends on the boiler.
And thanks alot, I will be calling for someone in Lars, and ill ask for this boiler. I just didnt want to deal with foreign brands, they take too long shipping parts, at least i heard.

 

[Dana]

Cast iron boilers can go a long time, but oversizing the boiler for the radiation by 2-3x cuts into efficiency. The combined thermal mass of the cast iron boiler and the volume of water & cast iron in the rads saved it from ridiculous short cycling, which would have been a longevity issue (primarily for the ignition & gas valve controls.) As long as the operating temp was above the condensing zone, the cast iron would still last a long time, though erosion on both the fire side and water side of the heat exchanger plates causes it's heat transfer efficiency to fall over long periods of time. There are many 50-60 year old cast iron boilers out there that are still running, but burning more fuel to deliver the heat now than they did when new.

If you calculate the actual heat load based on fuel use you would indeed be able to calculate the approximate water temperature you would need at the 99% outside design temperature, and fine-tune the "outdoor reset" curve as the cooler temperatures arrive. With out any sort of load calculation the starting point would be merely guesswork.

 

[brucewayne]

Hi Dana, ive still been looking for good deal, please let me know if this wont short cycle
ive decided to try a combination boiler that modulates, I cant tell if this offer is honest
i was offered an ibc boiler. Since it modulates between 20000- 125000 BTU
Does that mean, if i need 30,000, it would deliver as so, but if i need 50k, then it modulates and delivers any number per hour?


this is the boiler
http://ibcboiler.com/ibc-products/dc-series/


i dont like the fact its up to 125k though.

 

[Dana]

Seriously, combi boilers are at once too much (on the space heating end) and not enough (on the domestic hot water end.)

You have 175' EDR, so at 20,000 BTU/hr that will be 20,000 /175'= 114 BTU/per square foot, which takes ~155F water to balance, which is well above the condensing zone. If you run it at condensing temps it'll cycle. The thermal mass of the water volume & cast iron in the rads will probably keep it from self-destructing in short years, but it's far less than ideal.

And at 125,000 BTU/hr-in at the high fire end it'll support only one full flow shower in winter, without much overhead for other draws, which means you have to schedule your water use. (Don't shower while running the dishwasher or clothes washer, etc.)

 

[brucewayne]

oh now i see why i shouldnt get condenser.

if you have any recommendations, please let me know.

and what about modulation, that would still deliver precise btu?


if i ended up installing condenser boiler, it would still work with water based radiator? of course still short cycle right?

 

[Dana]

With 175' EDR of radiator you can get the thing to run at condensing mode without much cycling as long as it has a minimum modulated output of (70 BTU/hr x 175'=) 12,250 BTU/hr or lower, but to hit fully 95% efficiency or above you'd really like a min-fire output of (50 BTU/hr x 175'=) 8750 BTU/hr or lower. The maximum output of your radiators with 180F water would be the 30,000 BTU/hr you calculated, so you don't need a max output any higher than 30,000 BTU/hr, though higher is fine, as long at the min-fire output is below 8,750 BTU/hr. Here is a short list of boiler models that would meet your needs (but there are others.)

Boiler Model ........ Min. input .............Min. output (95%) ....... Max. input

NTI Trinity TX51 ........7,100 BTU/hr..............6,745 BTU/hr...................57,000 BTU/hr

Navien NHB 80...........8,000 BTU/hr..............7,600 BTU/hr...................80,000 BTU/hr

HTP UFT-80W............8,000 BTU/hr..............7,600 BTU/hr...................80,000 BTU/hr

Lochinvar CDN040 ....9,000 BTU/hr..............8,550 BTU/hr...................40,000 BTU/hr

Lochinvar KHN055 ....8,300 BTU/hr..............7,885 BTU/hr...................55,000 BTU/hr

Any of these boilers will run in condensing mode without short-cycling on your radiation if set up properly, and all will be able to deliver 180F water if you really need 30,000 BTU/hr of radiator output (you probably don't need 180F water ever.)

Modulating condensing boilers come with an programmable "outdoor reset" control, which increases the water temperature as the outdoor temperatures drop, and decreases the water temperature when the outdoor temperatures are higher. This has to be programmed for your climate, heat load, and radiation, but once it is tweaked in it will always keep the place warm, with very stable temperatures and a the maximum possible efficiency, running VERY long (nearly continuous) burns during the winter.

Please take the time to read this bit of bloggery to make sense of it all.

Not all of those boilers are equal in terms of ease of installation. The fire-tube heat exchanger types would be more straightforward, since they have simpler near-boiler plumbing, and can be pumped direct (one pump) the way cast iron boilers usually can. The Navien requires a hydraulic separator (they have a pre-made separator manifold that they're happy to sell you). The CDN040 can be pumped direct if you specify the pump correctly, but Lochinvar may void the warranty on that one if installed without hydraulic separation. The HTP UFT-80W, NTI Trinity TX51, and Lochinvar KHN055 are all fire-tube heat exchanger types, and preferred IMHO.

 

[brucewayne]

Thanks so much, its just one more concern, because last contractor mentioned the pipe to chimney was too small but its just duct work airing out whatever rubbish to the chimney. Also that only combi could be installed.

is there such a thing? wouldnt any boiler work? right now, i have a draft type setup, goes from boiler, tees off towards water heater, and keeps going up to chimney.

So i dont know what hes on about. I was under impression that any boiler can be installed, chimney or not. water tank or not. right?
if it helps, heres photo of the duct work. I thought you can install any boiler granted btu is fine
the bottom left feeds into boiler

extra pic if help plz

 

[Dana]

Condensing boilers use plastic vent piping, and is usually vented out the side of the house. You can't vent a condensing appliance into a masonry or terra cotta lined chimney, since the exhaust is too cool, and will condense/adsorb into the mortar. The acidity of the condensate will break down mortar over time.

Codes vary on whether one can install a plastic vent pipe inside a masonry chimney, but it's universally "no" if that flue is also being used by a non-condensing appliance. Whether the boiler is side vented or not, the atmospheric drafted water heater has to go (or be lined with a narrower liner more appropriate for the burner output of the water heater), or it too will condense in the bigger chimney if it doesn't have the additional burner capacity of the boiler to keep it warm enough during cold weather. The most common solution is to install an indirect fired hot water heater operated as another zone off the boiler at the same time the new boiler is installed. This approach works fine with old-school boilers too.