Triangle Tube or Cast Iron?

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Estrada

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I just bought a 50-year-old, 2500 sq. ft. house (two stories, doesn't include the heated basement) in the 60062 zip code, and I want to replace the boiler (original to the house) and the hot water heater with a boiler/indirect water heater. I have two contractors who seem very competent, one who immediately said the existing 160k BTU boiler is way too big, but only installs cast iron boilers, and another who installs mostly Triangle Tube, and quoted me their 110k BTU Solo (modulates from 30-110) (next one down is their 60k, which modulates from 16-60).

I assume the insulation is original to the house, and I don't know what it is. I'm having every window in the house replaced this week with double-paned, low-E windows, and before next winter I'll have most of the basement insulated (it isn't now) and probably seal and re-insulate the attic too.

My first and main question is whether the 60k Triangle Tube will be adequate. My second question is how put off should I be that the Triangle Tube contractor was happy to quote me a conversion to three zones without noting that the 110 is almost surely too big for that.

I'd appreciate any guidance.
 

Dana

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I just bought a 50-year-old, 2500 sq. ft. house (two stories, doesn't include the heated basement) in the 60062 zip code, and I want to replace the boiler (original to the house) and the hot water heater with a boiler/indirect water heater. I have two contractors who seem very competent, one who immediately said the existing 160k BTU boiler is way too big, but only installs cast iron boilers, and another who installs mostly Triangle Tube, and quoted me their 110k BTU Solo (modulates from 30-110) (next one down is their 60k, which modulates from 16-60).

I assume the insulation is original to the house, and I don't know what it is. I'm having every window in the house replaced this week with double-paned, low-E windows, and before next winter I'll have most of the basement insulated (it isn't now) and probably seal and re-insulate the attic too.

My first and main question is whether the 60k Triangle Tube will be adequate. My second question is how put off should I be that the Triangle Tube contractor was happy to quote me a conversion to three zones without noting that the 110 is almost surely too big for that.

I'd appreciate any guidance.

The Triangle Tube Solo 60 is almost certainly the right choice unless it's a solid masonry wall with no insulation, or if it's an unusual shape with excessive exterior surface area for a 2500' house and leaks a lot of air. With simpler shaped house with circa 1965 R11s in the walls with clear storm windows over aluminum single pane windows (so popular in the 1960s, a worst-case scenario) your heat load at -5F is probably on the order of 50,000 BTU/hr before insulating the basement, but less than 40,000BTU/hr after the low-E replacement windows and basement insulation. A mostly-rectangular 2 story is a fairly efficient shape, since the exterior surface area to conditioned floor area is lower than a 2500' rancher. If it doesn't leak great gusts of air and doesn't have an inordinate amount of windows you might already be below 45,000 BTU/hr, headed for 30,000-35,000 BTU/hr after upgrades.

With the -110 even the min-fire output of the -110 may be close to your design heat load, and will almost surely be over your average winter heat load. If you're going to go with a modulating boiler, it's a lot better for the boiler, your efficiency, AND comfort if it actually modulates most of the time. The -110 is probably their most popular boiler, but it's almost always oversized. In US climate zone 5 (that's you) the -60 would be the right boiler for at least 19 out of every 20 houses.

The number of zones and the amount/type of radiation on each zone matters too. To get condensing efficiency out of the boiler the radiation has to be able to emit enough heat at low water temps without short-cycling the boiler. Breaking it up into three zones is fine if he did the math on the radiation at 28-29,000 BTU/hr, but unless it's high mass radiators (or at least cast-iron baseboard, not fin tube) it's unlikely that he did.

The fact that he even suggested the -110 for a 2500' house isn't a good sign.

If you have a recent gas bill with the EXACT meter reading dates and fuel use over that period, it's possible to put firm upper bound on your actual heat load of the house in it's where-is-as-is condition, using the boiler as the measuring instrument. We would have to download a base 65F heating degree-day (HDD) spreadsheet from a nearby weather station on degreedays.net, and come up with the input-BTUs/HDD, then convert that to output-BTUs/degree-hour using simple arithmetic. With that constant you then multiply by the number of degrees between the presumptive heating/cooling balance temp (65F), and your 99% outside design temp. Your true 99% outside design temp is probably closer to 0F than -5F but it's fine to use -5F, since we're just ball-parking it here.

That would make it 70F heating degrees x your calculated BTU/degree-hour = BTU/hour of heat load.

If there is both an input & output BTU on the boiler's name plate use output/input for the efficiency. If not, use 80% (even though a 50 year old boiler is probably doing no more than 75% combustion efficiency after that many years of service.)

If you want to share the meter reading dates/fuel use info I'll walk you through it. But unless the resulting number is over 75,000 BTU/hr, the smaller boiler is going to be the right way to go, and will cover the "after window & insulation upgrades" picture with margin. The basement insulation is likely going to cut over 10,000 BTU/hr off the load, and the window upgrade is probably going to knock another 5000 BTU/hr or more (depending on what the "before" windows are, and how many total square feet of window you have.)
 

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Very much appreciated, Dana. That puts detail to my own inchoate sense that the 60 is the way to go. The house is not unusual, the new windows are in, and it doesn't feel drafty at all; everyone who walks in notes how toasty it feels. And I also managed to get in touch with an energy auditor and he's doing a manual j on the house in a couple of hours. I'll report back. Thanks again.
 

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Very much appreciated, Dana. That puts detail to my own inchoate sense that the 60 is the way to go. The house is not unusual, the new windows are in, and it doesn't feel drafty at all; everyone who walks in notes how toasty it feels. And I also managed to get in touch with an energy auditor and he's doing a manual j on the house in a couple of hours. I'll report back. Thanks again.

Run the fuel use calc as a sanity check on the Manual-J, since there are many ways to screw up the Manual-J. I've seen well intentioned people come up with numbers that would be greater than the source-fuel BTUs in a fuel-use calculation, and for sure the boiler that heated the space can't deliver more heat than the source fuel that went into it.

The fact that the basement isn't yet insulated will add quite a bit to the Manual-J. If you can, see if they can quickly re-calculate with the "after basement insulation" numbers, not just the as-is numbers. Or, you could just look at their basement loss numbers and guesstimate the post-insulation reduction.
 

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Ok, it's done, and the guy who did the Manual J was an old-timer who was bemoaning the fact that no one knows how to do them anymore, which I took as a good sign. He ran the numbers with the new windows, and also assuming that I would insulate the basement and put R40 in the attic. He came up with 51,000. Sounds reasonable, and close to what you estimated.

The complication now is that the net output of the Triangle Tube Solo 60 seems to be 47? I realize that the 51k number is for the coldest day of the year, and my use will be less than that for 99% of the time, but it does make me a *little* nervous to be close to the line (I'll also have an indirect water heater, but my understanding is that priority mode makes that irrelevant unless everyone decides they need a bath on the coldest day of the year).

If I don't go with the Triangle Tube because of their funky size steps, is there another mod/con boiler w/ indirect heater that I should look at? Since I'm in a big metro area, I figure I can find a good installer for whatever works.

Once again, a big thanks.
 

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With insulation in the basement and R40 in the attic and U0.34 windows I'd be surprised if the true load was over 38,000 BTU/hr. My "after" picture estimat was:

"...headed for 30,000-35,000 BTU/hr after upgrades."

His Manual-J came out ~50% higher than that, which isn't very close at all in my book. It's hard to know where the next 15,000 BTU/hr came from. Seriously, I've seen many ~2500' houses with uninsulated basements that came in under 50K @ 0F, and none that were over 40K after air sealing & foundation insulation.

What was he using for an outside design temperature?

What did he insert for a ventilation/infiltration load number?

A totally dumb I=B=R WAG on a 2-story ~2500' house with 3' of above-grade R10 foam insulated basement, and 350 square feet of U0.34 window, 45 square feet of 2" solid door, assuming a rectangular footprint of 31 x 40', an indoor design temp of 70F, outdoor design -5F (75F delta-T) and R40 in the attic:

Attic U-factor ~0.035. Attic floor area 1240'. Attic losses are:

U0.035 x 1240' x 75F= 3255 BTU/hr

Wall U-factor ~0.08 (including the above grade basement wall). Assuming 11' per story + 3' of above grade basement the gross wall area is perimeter x 25' of height, less windows and doors. The perimeter is (31+40)x 2= 142', so the gross area is 25 x 142= 3550'. Less 350' of window leaves 3200', less 45' of door leaves 3155' of wall. Wall losses are:

U0.08 x 3155' x 75F= 18,930 BTU/hr

Window losses:

U0.34 x 350' x 75F= 8925 BTU/hr

A 2" wood door has a U-factor of about U0.50. Door losses are then:

U0.50 x 45' x 75F= 1688 BTU/hr.

Add it all up and you're at 32,798 BTU/hr.

Throw in another ~5K for below grade & slab losses plus air infiltration and you're still only at 38K. From there you start subtracting for the warm bodies and plug loads (250 BTU/hr per sleeping human, another 300-350 BTU/hr for the refrigerator, 200-300 BTU/hr for the TIVO, etc.)

If you assume the place is a leaky sloppy 20ACH/50 wind tunnel for air tightness (not likely if it feels snug and not drafty) you might hit 50K, but I'm not quite buying his numbers, unless my crayon-on-napkin model of your house is dramatically different from your actual house. Before basement insulation it's probably over 40K, but not by much.

A U-factor list selected at random from the web for sanity checking my number lives here.

Regarding boiler output, and alternatives...

The DOE output of the Solo 60 is 54,000 BTU/hr, not 47K, which is the IBR output number. If you are installing the boiler out in the garage, on the other side of the insulation you'd use the IBR number, but if it's going in the basement, the distribution and jacket losses accrue to the heat load of the house, and are not lost, thus the DOE number is the right one to use. So even if his 51K number is right (not likely), if the boiler is in the basement you're still covered.

The smallest Lochinvar Knight has comparable output numbers with smaller steps in the series than the Solo, but I'd still be recommending the WHN055 over the WHN085 for your house, since your likely average winter load is maybe only ~50% more than the min-fire output of the -085. The -055's output is about 10.5K @ min fire, which means it can still modulate well into the shoulder seasons.

The Burnham ALP080 is another option, with a high-fire a bit bigger than the Solo-60, but with the same min-fire (though still higher than the WHN055, and not much lower than the WHN085).

Way out in left field, but still worth thinking about, the HTP Versa Flame or Versa Hydro combi heat/hot-water systems work well, and are inherently self-buffered by the thermal mass of the hot water tank, making the comparatively high min-modulation range less important. The fact that the max output is more than 2x your calculated heat load (and ~3x your likely actual heat load) gives you less to worry about, and it takes up barely more space than a 50 gallon standalone HW heater.
 

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Thanks much once again. He did say that he thought it was "a tight house," so based on what you say, I'm now surprised by 51k too. He's going to email me the report and I'll post those details as soon as I have them. I hope there's something obviously off with his numbers, because I have a slight preference for Triangle Tube just because the installer is local, and seems to have installed a lot of them (I'm guessing Triangle Tube doesn't fly any old installer to Belgium).
 

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"I'm guessing Triangle Tube doesn't fly any old installer to Belgium"

I dunno, that could be a hazard- do they offer extended brouerij tours for their ace installers? (Not that chuggin' suds ever slows the Flemish down... much. ;-) )
 

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Ok, I got the report and one difference is that he's included the finished portion of the basement at around 500 sq. ft. with a loss of 7500. The rest I'm not sure how to read, but if I'm using the file upload correctly, you should be able to see relevant numbers in the linked file.

Edited to add: Looking at it a bit more, he has a U factor of 0.54 for the windows, but they're actually 0.30. The stickers are right on the windows; sadly I'm not there to check to see if the stickers are wrong or if he is.
 

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Beads

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Why rush, is the current boiler in bad shape? Why not wait while collecting some data and making improvements before you make one of the biggest investments that you will have in the whole house fix-up? Get gas use records and all the rest of your data lined up before you decide. How much is it going to cost you in fuel to run that boiler for another year (or two) compared to a new one? The very general rule is to insulate and seal it up first and then pick equipment for the new demand.

You will find that a lot of people are fans of de-zoning homes when retrofitting low mass boilers, especially in low demand homes. With less mass, you need to match the heat source to the demand more closely. Sometimes the modulating boilers can't modulate low enough with a model that meets the demand of the entire structure in the coldest times. Sometimes, however, one zone can't keep the home comfortable due to large differences in demand, like a basement compared to above ground.

Dana may recall that he mentioned the HTP products to me wrt my dad's house. I am thinking that it is the best fit for zoned application. I had a hard time distinguishing the Versa-flame from the -hydro. It seems that the former operates up to 180 F while the latter has a max temp of 160. The -flame uses the water-water heat exchanger for domestic hot water while the -hydro uses the heat exchanger for the heat. I'd wish for a lower capacity model despite the buffering. It makes me wonder if it would be worth installing a heat exchanger in conjunction with their Phoenix Light duty water heater.

It seems to me that some of the physics behind HTP's efficiency with the primary HX in water tank design is the polarization of the water temperature within in the tank. They maintain cooler the bottom where the flue gas is also coolest. I'd like, however, to see their efficiency numbers at different temperature settings.

Some boilers can lock out the highest fire. That appears to help because they start up at 100% and then drop down. Sometimes that gets the zone calling for heat into an inefficient run (very hot) right out of the gate and then it shuts down quickly too. I think it is inherent in these systems that they are at higher efficiency at low fire because the primary heat exchanger saturates (gets hot from one end to the other).

Here is an example where the study directors locked even an HTP Versa out of high fire. It is also an example of how difficult it is to fit a lightweight boiler to low demand with the available boiler capacities, although I think the size thing has improved since this was done.

Search for this and make sure that you get the whole 70-odd page report and not just the short summary, preview or plan:

"Optimizing Hydronic System Performance in Residential Applications"
 

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"is the current boiler in bad shape?"

I don't think so. It's old and paint is peeling off it, and something that looks like a cowl is loose, but the house is warm and for all I know it'll run another fifty years. The home inspector thought the hot water heater was on its last legs ("popping noise"), but I can't evaluate that either. But assuming that's true, I'd rather change the boiler too and do an indirect tank (we get a bunch of guests often enough that I worry about capacity) instead of getting a new water heater now and dealing with the boiler later. In addition, I'm not sure how much added precision is going to affect the decision at this point. Even by the maybe-too-high Manual J that was done, the 60 looks fine.
 

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The more I look at the report, the less sense it makes to me. It *looks* like the U factor he used for the windows is 0.57, but the windows are 0.30. SHG for the windows is 0.28. And I have 96 feet of radiator (covers) in the house. When I asked him about the U factor, this is what he said.

"The factors in my program were lower than what you actually have or the ones I used or various factors that were higher. The ones I used are also for very efficient windows. With the amount of radiators you have in the house if you use too small of a boiler you will not be comfortable in your house. I agree with you that you were getting overkill on your bids but we want to make sure you don't put something in that isn't going to satisfy your needs. The factor difference would make very little difference in the load."
 

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Beads: "Why rush, is the current boiler in bad shape?"

The boiler is old enough to qualify for an AARP. This is not rushing, this is prudently retiring it before it springs a leak.

Even if the paint on the sheet metal is all nice & shiny, at typical degradation/erosion/corrosion rates on the heat exchanger plates a gas-fired cast iron boiler that started out at 80% steady state won't be doing better than 75% steady-state after 25 years of well maintained service. If the thing is 3x or more oversized for the peak heat loads (almost guaranteed to be, for the house in the "after" condition of the building upgrades) it won't be getting better than 60% average efficiency due to cycling & standby losses + low combustion efficiency. By being ridiculously oversized for the load it can still heat the house even if it's only running 40% efficiency, but it doesn't make sense to wait until both the fire & water sides of the heat exchangers are worn smooth, with lower surface area and no turbulence to help out on heat exchange efficiency.

The Manual-J has a significant thumb on the scales if he used U-factors of the windows that were nearly twice the actual U-factors. If there is a line item for the total window losses, cut that in half: 2 x U0.28=U0.56, which is still less than the U-factor he used, 2 x U0.30=U0.60, which is only 5% more than the U-factor he used.

This is EXACTLY the type of sloppy, not very aggressive or accurate heat load calculation approach that leads to oversized equipment. No matter how good the program & method, garbage-in=garbage-out. If the unconditioned crawl space is going to sealed & insulated, that's another thumb on the scale. "The factor difference would make very little difference in the load."

Really? What is the point of even calculating it then? With 10% here, 50% there, pretty soon you're talking about significant differences in load. A window with U-factor 0f 0.57 isn't even code-legal to install in IL. Most clear-glass bottom of the line vinyl replacement windows have U-factors of about 0.50 (still not code) which is 10% more efficient than his "...very efficient windows". U0.57 is only "very efficient" compared to an aluminum framed clear single pane window.

His argument that the radiators are too large for comfort when using a small boiler is also complete BS. That notion only makes sense if you intend to use a deep overnight setback strategy, which is never the best way to use or get the highest efficiency out of right-sized mod-con. It makes sense for getting more efficiency out of a 5x oversized high mass behemoth though, since at least the intial burn is long, and not a short-cycle.

Are the radiators under the covers high-volume cast iron column radiators, or are they finned convectors in a sheet metal housing?
 

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Thanks, Dana. It's nice to have someone knowledgeable confirm my suspicions. He was almost done with the measurements when he told me, hey by the way, we sell boilers too, I'll send you a quote. Nooooo. Anyway, the radiators are not cast-iron, they're convectors--about eight inches high on the floor (also original, I'm sure). At this point, I don't see any reason not to get the Triangle Tube 60 with an indirect tank for hot water.
 

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If he was charging you $100/hr for his time it's a gouge. If it was a freebie subsidized by the utility or something it's somewhat less egregious, but not exactly what I'd expect from a professional.

Fin tube convectors have very little thermal mass, so if you're breaking it up into zones you have to be sure that there is sufficient output on any ONE zone to emit the ~15,000 BTU/hr min-fire output of the Solo 60 into the zone with ~120F average water temp if you're going to get any efficiency out of it. If it's all plumbed with 1.5" pipe or something fat there may be sufficient thermal mass in the plumbing to limit short cycling, but be careful how you break it up.

What are the BTU input/output numbers on the cast iron beastie (is the 160K input or output? If the boiler doesn't cycle on/off during extended calls for heat we can use the boiler output BTU and the water temperature to estimate the output per foot of convector, and from there infer what the output per foot is at 120F AWT. To test that you'd have to bump up the thermostat by 3-5F and take some temperature measurements on the output & return water.

Say you take some measurements, assuming the old boiler has a rated output of 160,000 BTU/hr, and during a long call for heat the boiler's temp stabilizes at 190F, with 170F return water, for an average water temp of 180F. With something like 80 feet of actual fin tube inside those 96' of convector cabinet that would be something like 2000 BTU/hr per foot @ 180F (which might be about right for 4" fin tube). The output at 120F AWT (nicely into the condensing zone for the boiler) will only be about 1/3 of what it is at an AWT 180F, call it ~700 BTU/ft. To balance with 15,000 BTU/hr of min-fire boiler output it then takes a minimum of 15,000/700= 21 feet of fin tube to be able to run a zone at condensing temps without cycling.

But we need the real numbers, this was just an example based on insufficient real information. It may or may not be in the right ball park. (Note, with the Solo 110 you'd have a substantially larger minimum zone radiation size to balance reasonably without cycling at it's much larger min-fire output.)

Other than direct measurements we would need to figure out the approximate output based on the actual size of the fins and the fins per foot, the actual length of the finned section in each cabinet, etc.
 

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Right after my previous post, when it became clear that the 60 is probably the way to go, I figured it was wise to get another quote, and called the regional Triangle Tube rep to get a name. Just met that guy, and he took complete measurements of the house, and even crawled up to the attic as a matter of course. His eyeball guess was that the 60 is sufficient, and his final load numbers I'll trust, but those aren't coming until Tuesday or Wednesday. Once again, thanks, and I'll update as soon as I have that info.

Edited to add: the existing boiler is a 160/128.
 
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Dana

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But that's thick & tall fin-tube convectors, not baseboard. They look something like this(?):







With 128K of boiler output, that' 1333 BTU/hr per running foot of convector, which probably settles in at ~150-160F average water temp (say, 170F-180F out, 150F-160F back) during extended calls for heat, say, when recovering from a deep overnight setback?
 
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Estrada

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The cover grates look like that, but they're on the ground and about eight inches tall. But you got the dust right. Hoping for the new load analysis today or tomorrow.
 
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