Looking for recommendations for old OVER-sized boiler

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JBurdman7

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Cheat sheet:
69 degree temp differential indoor / outdoor
1969 Hydrotherm cast iron boiler Model R-180 NG burner runs 26.66% of the time

All? The details…
I live in East central PA where we go a little below zero on the dozen coldest nights of a typical winter. Double digit below zero windchills are about as bad as it gets.
Home is post WWII wood frame, blown-in insulation, new windows, nearly all leaks sealed etc.
Boiler is a Hydrotherm installed Aug 1969. 180,000BTU in, 144,000BTU out
Gas valve, thermocouple, and tank thermostat independently failed / replaced 20-30 years ago.
I vaguely recall measuring the stack temp at 550F but I don’t recall for certain if the boiler was set to 180 F.
Pilot light, millivolt system, can gravity feed in a power failure.
I typically shut the pilot off in the summer.
I set the flow valve to be always open in order to have the gravity feed at hand. That valve is probably from 1946. The zone valve I leave electrically trigger. I have to open that in a power failure.
Sqft maybe 2,300, not sure
Radiation is finned wall registers. There are plenty. The burner would probably run continuous, or just about, if the tank temp were set high.
The basement is on its own zone but if that zone is allowed to trigger independently, we get leaks. The theory is the sudden expansion-flexes. So the basement zone is set to trickle when the upper floors call for heat. Never a leak doing that.
Thermostat stays at 71-72 F main floor. Basement trickle is adjusted to maintain 64+-. All radiation upstairs (small knee-wall rooms) is shut off and varies in temp, generally 60F and up, depending on ambient.
Until the temps start going below freezing I leave the boiler set at 160F. Once we start regularly going below freezing I go to 180. Then when spring gets closer, back to 160.
Flu is terra cotta lined, with the opening placed oddly low on the wall. We use a short NG tank DHW. Some 30 gallon shorts won’t even fit. 4 bedroom house but only 2 occupants so no worries. Might ding the resale value tho unless I get a tankless (next owners problem IMO.)

I don’t mean to bore you but you know how it is… if I err and no one catches it, we could chase the wrong rabbit.
Early in the morning Jan 21, 2019 ; 3F 12?MPH winds; I measured the boiler circulator on time with tank set to 180F as:
1:03AM turns on
7 minutes, I was upstairs, not sure if all was all burn time. I couldn’t hear
1:10 turns off
off for 17min 15 sec

Turns on 1:27:15AM
burner comes on ~45 sec later
1:33:30AM all shuts off
so a 5min 30 sec burn

after 17min 30 sec off
burns for 5min 45sec
All off, for 16 min

Ergo burner is on an average of 6 min (worst case) for every 16min 30 sec off
or 6/ 22.5 of the time = 26.66%; 26.66X 144,000BTU = 38,400BTU demand

I only water the system right before the heating season and if I hear any gurgle I’ll shut the heat off off, let it cool, and turn the water feed on again for a bit. I’d rather do that than risk coming home to a nasty leak. All has been well but the place is pushing 70yo.

Is that everything? My apologies if I forgot anything useful.

I have a sense of what improves efficiency but not much of an idea about what will kill the boiler quicker.
I know enough to know that I want to set the boiler temp back, as I do, that is about all. I never pushed that because I don’t know how far would be too far. I don’t care for making the circulator run a lot anyway.
I suspect that I should fashion a delay to make the circulator run longer, but I have no idea what temps to shoot for.
I suspect that a flu damper would help, but I doubt I have the height to install one, I also suspect that doing such modification for a 50yo plant would not be wise.
Is there anything I can do that would make the plant more efficient? I’m a tinkerer so the parts and labor would be near zero.
Also, any suggestions as to what plant this should be replaced with when it finally springs a leak? Not sure what a building inspector might think of seeing a 40,000BTU system tho.

All tips and comments appreciated! Thanks!
 

jadnashua

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You can't let the return water get too cool or condensation will eat up your flu. On those cold days, though, it would be better if it were sized so it ran a lot more. I don't know enough about them to know if the burner can be downsized much, if at all.
 

JBurdman7

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The first story of the flu goes thru an unheated garage which is typically in the high 40s and very rarely goes below freezing. The second story goes thru an enclosed unheated porch which seems to maintain ~1oF+ above ambient. The third story is exposed on 3 sides to all weather.

You've given me the excuse I need to never vacuum my radiators again!! :D
I could go around and block the air flow into the radiators by a certain fraction if we can determine how much blockage would deliver the desired results.

The temp outside was 32F. I just finished measuring the water inlet temp.
Starting at 80F
heat called for circulator and burner running
85F @ 1min
90F 1m23s
95F 1m38s
100F 1m55s
105 2m31s
110 3m52s
112 at 4m17s demand met. All shut down.

The burner is 3 jets, each feeding 3 3/4" wide portion of the rack. I don't know if this is practical but removing the outer two jets would theoretically take me to 48,000BTU output. I guess that the flu would also need restricted by 2/3. If the heat exchanger would be OK with only being heated from the center. The pilot lights between the center and left racks so that shouldn't care.

Thanks!
 
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Dana

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There's way too much slop in the duty cycle measurements unless you log the duty cycle over many days or at least a few weeks against the outdoor temperature. It's easier to just use the efficiency of the boiler (144K/180K= 80%) and the fuel used over winter billing period (exact meter reading or fill up dates and amounts) against heating degree-day data from a nearby weather station. The details of how to go about that napkin-math approach live here.

The ~27% of 144K number probably isn't all that wrong (it's quite credible, in fact) but a snapshot over a few days or hours has potential for significant error. Let's say your heat load at the 99% outsided design temp is 144,000 BTU/hr. ASHRAE recommends an oversize factor of 1.4x to be able to use overnight setbacks and cover the Polar Vortex type cold snap. That would bring the boiler output size you're looking for to 56K. If it's a cast-iron boiler you'd be looking for something with a DOE output as clost to that as possible. But these days it can be cheaper and more efficient to install stainless modulating condensing boiler, and with a reasonable modulation range it can still be significantly oversized on the high-fire end and still have sufficiently low output at low fire to not short-cycle even at very low highly efficient water temperatures. I doubt you'll run into any problems at all with a 60-80,000 BTU/hr modulating condensing boiler, that would run nearly continuously at very low fire if it has a 7:1 or higher turn-down ratio. The napkin math for the radiation analysis live here.

Most of the water tube type heat exchangers used in mod-con boilers can't handle the full flow of many heating systems if pumped direct, and need to be plumbed primary/secondary adding to the cost of installation, but most water tube type boilers can be pumped direct for most fin-tube convector type systems (though some installers and manufacturers still recommend primary/secondary even on really simple, modest-flow systems.)

With a small mid-efficiency cast iron boiler you'll need to install a narrowing flue liner to keep stack velocity high enough to limit condensation or prevent backdrafting, which adds to the expense. With the radiation oversized for the boiler the boiler would have to be protected from too-cool return water to prevent destructive condensation inside the boiler (though there are some tiny Burnhams that self-protect down to 110F return water temps internally), which can also add to the installation expense. A small mod-con can be vented with cheap plastic flue (even out the side of the house, allowing you to seal up the 24/365 parasitic infiltration driver called "the chimney"), and their combustion air can be piped making it a "direct vented, sealed combustion" system with NO possibilities of backdrafting.

I suspect that with the beastie boiler out of the way there would be space for a 40-50 gallon "indirect" fired tank next to a wall-hung mod-con boiler. If the hot water is given priority by the zone controller an 80K mod-con will support a 24/7/365 shower, but even a 50K mod-con has more burner output than a typical 50 gallon standalone, and the tank recovers very quickly, way to quickly to notice that the space heating had been interrupted for the boiler to serve 100% of it's output to the water heater.
 

JBurdman7

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So in a nut shell, and to be sure I'm understanding correctly, because a proper install of a cast iron unit would have its own complications, it would be a waste to not to go the route of accepting the complexity of installing a mod-con instead so as to take advantage of the now excessive amount of radiation in the system. I'll do more calculations but we all suspect that a 60-80k unit is the right ball park. Excellent!

Is there anything that could be done to make the current system function better? It sounds like I could restrict the air flow to the radiators to increase the EWT. It would be simple to cut some AL foil and lay it on top of say 1/2 of the fins... assuming that will not result in some disaster from changing the thermal expansion for different sections of fins. I could keep restricting until the EWT gets to 140 before shutting off. I rather doubt that the circulator runs long enough to get the hot water back around until it gets to be in the 20s outside but I'd have to check. Here I was thinking that the recommendation might be to purge the tank after each fire, but that would only lengthen the off time, which would decrease the start-up EWT.

Perhaps when its cold enough out I should lock the call for heat "on" until the return water gets to a certain temperature, ~140?
I suppose it is safe to assume that no one wants me to wire a second thermostat to fire the tank to 140 once after each shut down to dry the heat exchanger. Or to use the gravity feed, or valves, to slow the water flow down to try to raise the exchanger temp.

Also, if anyone knows, or could tell me how to find out, if this Hydrotherm could be adapted to employ a ~60k burner, or if I could disable 2 of its 3 burner racks, to make it a 48,000BTU unit. Or at 50yo am I just whistling past the graveyard with that line of thinking? I don't know. The water is soft in this area, if that helps. Maybe it would still be worth replacing the gas valve should it fail again. That was not a cheap repair as I recall.

Then again, if the unit is made to be 48,000BTU, will it run longer but still have trouble getting the EWT to 140? I may have to restrict the radiators in any scenario short of a installing a condensing unit. Actually at 48,000 I'm thinking I could just set the thing to gravity feed.

I thank everyone so much for sharing their expertise. I know in this area anything but cast iron is frowned upon. To have a real discussion about getting things right, rather than suffering people pushing what is easiest for them, is fantastic!
 

Dana

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I've been assuming this is pumped hot water, not steam, (can the R180 do either?) but perhaps I've been wrong in that assumption. The reason I'm question it is the statement.:

"It sounds like I could restrict the air flow to the radiators to increase the EWT."

There should be no air in the system, only water.

Throttling back the flow to the radiation does not improve performance, but is sometimes necessary to balance tempertures between rooms/sections when it's all operated as a single zone. Breaking it up into separately controlled heating zones (usually by floor) is often the best solution.

Installing a mod-con boiler isn't usually more complex than cast iron, but the multiple parameters that need to be set up and verified take more time than tweaking a couple of aquastats. To the extent possible YOU should be the one tweaking those parameters to get the best performance & comfort out of it. Many installers just set them up to run at the maximum temperature all the time and walk away, due to the time consuming aspects of setting them up properly.

Down firing gas boilers with the tubular burners doesn't really work well. Since there are no combustion-air adustments on that type of burner, down-firing it results in ever higher excess combustion air, and lower raw combustion efficiency.
 

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Upon re-reading (post coffee :) ) I get it- you are talking about restricting air flow through the air side of the convector.

Yes, restricting air flow through the convector fins will reduce the output by quite a bit, and won't damage the convector. The air dam can be almost anything, but aluminum foil is fine, easy to size & shape, and won't melt at any heating system temperature.
 

JBurdman7

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Yes, pumped hot water. The radiators are like a baseboard except they are incorporated in to a 2' tall steel box to create a chimney effect. They do not have water flow valves. I think they are supposed to be adjusted for output by a metal flap that lays down over the fins. We're the 3rd owner here and those flaps are all missing. Incidentally most of these radiators are recessed in to the wall. Nearly 20 years ago I got 3/4" foil backed foam which I cut to fit in the back of all of the radiators which were on outside walls. I haven't noticed any condensation issues. I wasn't keen on applying heat to the least insulated portion of my envelope haha.

A "tube burner" makes me think of a gas dryer. I wish I knew what the differentiating details might be but I'll try to describe. There are 3 gas jets, each firing in to a tube with an air adjuster, and each run to a large cast iron grate about 3 3/4" wide and maybe 15" deep.

If the combustion air is the only complication to down firing, is that a surmountable engineering problem? The boiler has a fairly large air entrance at the rear. The front has some capability to pull in air but not much. Would it be possible to plug the 2 burner jets on the sides, just fire the center, block the flu at the vent hood by 2/3 (essentially install a metal pie dish with a hole in the center the correct diameter), then block the rear air entrance roughly 2/3, until the flu temps matched or were a touch below the pre-down firing temps, all else being equal? I practically live in W Va as far as zoning laws. No one will know what I'm up to.

If I do these changes, should the circulator's flow rate be reduced by a motor speed controller? It is a 1/25HP Taco 007-F5 just in case that is as miserably mis-sized as the rest.

I'll restrict the air to the radiators. Is there any rule of thumb I can go by as far as what return temp I'm shooting for under some specific test condition?

There is a 40Gal NG DHW on the same chimney. I never noticed condensation running out of the cleaning door for the flu. There are a few streaks on the wall of previous water ingress but I'm willing to bet this was from heavy summer rain(s).
 

Dana

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Most newer boilers don't have individual combustion air adjustments on ribbon-burner tubes, but I guess 50 years ago they were still doing that, eh? The details of your burners don't sound too familiar, but there are many variations on the theme. You may be able to down-fire it some without destroying the boiler, but at 3x+ oversizing not enough to make a measurable difference in fuel economy or comfort. If down-fired too much the flue will be too oversized for the BTU input to operate properly, risking backdrafting, and the raw combustion efficiency starts to fall off at even a 25% down-firing. Since the combustion air is adjustable on your burners, have you tried adjusting them for optimum efficiency?

I'm familiar with the type of convectors you have (and they can be used with both hot water or steam.) I was just having a mental-lapse. (More sleep needed, more coffee, maybe both.) It was common to cut them into walls usually under a window to limit window condensation before the 1970s energy price shocks. The foil-backed foam will make a difference in the heat loss, but be aware it's a fire-code violation to not have a timed thermal barrier against ignition. (Though it is not a particularly hazardous violation given the limited size and placement.)

Flue condensation on gas burners is almost never visible as liquids on the surface. The condensation happens at the coldest part of the flue, which is at the top, and gets absorbed into the terra-cotta liner and mortar, and it's primarily only cold enough during the winter for much condensation to happen. In July the top of the chimney averages 50F or more warmer than in January.

As long as the entering water temperature at the boiler is 130F or higher during the majority of the burn time there is effectively zero chance of condensation inside the boiler, and on an 80% efficiency boiler 130F entering water temps won't increase flue condensation either. Lowering the operating temperature of the boiler can save a percent or two on distribution and standby losses for every 10F drop in average temperature. There may be a bypass branch in the near-boiler plumbing mixing boiler output with the return water to keep the entering water temp at the boiler above 130F, a common strategy for systems with high-volume radiators, but that isn't always done with convectors since there is far less thermal mass to heat up.

Taco 007s are fixed-speed- there is no adjustments or controls to be made there. If the flow needs to be adjusted downward (not likely), a ball valve in series with the pump does the trick. Most systems are set up to have a 20-25F temperature drop from where the water enters the radiation loop and where it returns back to the boiler. If it's going out at 170F and returning at 160F (a 10F difference) it's over-pumped, and slowing the flow a bit may be worth it. As you lower the boilers output temperature the in-to-out delta will shrink, but it's fine to have 140F-145F out with a 130F return, but not 125F return. If the water is going out at 180F and coming back at 140F (a 40F delta) it's worth considering increasing the flow with a more powerful pump.

If you're keeping this boiler it will be worth installing a heat purging economizer control such as the Intellicon HW+ or Hydrostat 3250 Plus, which will automatically reduce the average operating temperature of the boiler. At your oversize factor you can expect 15% (sometimes more) reduction in fuel use.
 

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I thank you kindly. That video was excellent. All I knew is the flame was blue with pops of yellow. The pops seem to be dust as the adjustment doesn't seem to change that effect. Tho there have been a few techs over the years who claimed to have adjusted the burner, I found the adjustments WIDE OPEN. I have three separate gas jets feeding 3 separate burners, all cast iron if that matters. I adjusted two while PB Blaster worked on the third set screw.... then I broke a Craftsman screwdriver on that one. So I cut apart a V8 "soda" can and slid two pieces behind the adjust wheel until I got it right, then bent the can over. Where there is a will, there is a way ;) I think my elevation is only a few hundred feet here and the adjustments are now around half closed. I couldn't get as good of a look at the top of the flames as in the video you linked to but the flames were undoubtedly fluttering before the adjustment. The unit definitely runs quieter now.

Hydrotherm R-180.jpg


I blocked off another 7.5ft of radiation. There were 13ft blocked before, for a total of 20.5ft now blocked.
There was 22ft of radiation in service before, now down to 14.5ft, out of a total 35ft on the main zone.
The basement has about 18ft. That has its own zone but the zone valve is forced open and another valve is adjusted to a trickle so that it stays about 63F.

I experimented with the accuracy of my thermal couple by measuring the temp of 170 degree water comparing immersion to reading externally and found I'm under by ~10F when measuring externally. So all of my previous EWT measurements are low. I'll add 10F to my numbers from here on.

Before the primary air adjustment I measured my boiler outlet temp at 150 at shut off.
After the air adjustment I measured 170F at the outlet at shutoff- but shutoff would have been at an abnormal period because I shut the heat off for awhile before adjusting the burner air so it would run long enough to allow adjustment. EWT was 125F at boiler shutoff. 27F ambient. This is after having blocked the additional 7.5ft of radiation. So I set the boiler temp back to 170F so the pump will run longer and hopefully be returning hotter water to the boiler before the heat demand is met. That seems to have helped. There is no bypass branch. It takes a few minutes for the return water to be anything but very cool. I do not understand how a purging device would help. I'm struggling to keep the system temperature up. I'd have no trouble operating this as a condensing unit except I guess that would kill it fast.

It would seem a shame not to get a condensing boiler to make use of the excessive radiation when this Hydrotherm goes. I'll be out of here in 10 years or less so hopefully that won't be my project, but I am leaving notes on everything for future owners to reference! The basement loop could be plumbed to be a secondary loop taken from the upstairs' return water. Then there should never be an issue with keeping that in condensing mode. It would be "use it or lose it" free latent heat at that point.

I don't like the idea of trying to heat the boiler from only the middle burner anyway. I don't think that if I were cast iron that I would appreciate the temperature differentials that would cause. I don't suppose that I can reduce the gas pressure by half or more, re-adjust the primary air, and restrict the flu? I can't game out in my head if making the flame 1/2 - 1/3 the height would give a usable result.

I always knew this installation was wHay out of whack. If you can think of anything more that I should try please let me know. I appreciate your advice so much! I will watch the temps in different rooms and perhaps block more radiation. I can experiment with different tank set temps. That is all I know to do at this point without undertaking a re-engineering of the boiler, complete with "Oh my, I hope the insurance never finds out" flu restrictions and other such gutsy mods. They can already enjoy the customized V8 can air adjust mechanism haha! :)
 
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JBurdman7

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This morning I was available when the temp was -1.4F so I took a new set of measurements with the new burner adjustment being the major known difference, along with the changes made to raise the EWT. For each of the 3 cycles I measured, the burner ran for an average of 4 min then shut off temporarily while the pump continued, then burned for an average of another 50 seconds before the heat demand was met. I've since put the boiler temp back to 180 so it just does one burn.

Each burn totaled an average of 4min 47 sec over the course of 3 burns over a total of 64 min.
13.5min on / 64 min = 21% * 144,000BTU = 30,240BTU @ 70 degree differential. Outside was 3.6 degrees when I completed the test.
This puts my recommended size at 43,000, perfect if it ever hits 27 below again like it did 25 years ago haha. Do mod-cons come that small?

The last test, with the previous burner air adjustment, resulted in an errant heat demand of 38,400BTU.
If 21% duty cycle = 30,240BTU then a current (post air adjust) 26.66% duty cycle would produce 38,390BTU, for real this time.
If 8,150BTU / 38,390BTU was lost to the poor air adjustment then there has been a 21.23% improvement in output, even after the raising of the system temperature. Assuming I got the math correct and solar gain and other variables aren't messing with us too much.

Wow. 49 years of running 21% under it's capability? Unreal.
I suppose it is not useful to do the heat demand calculations based on the gas bill until I have an entire billing period with the new air adjustment.

At 2F ambient, 170F boiler set temp. Burner was shutting off when I was measuring 150-158F at the output. I don't know if that sound about right or if there is a problem with the measuring device I am using.
The output water temps ran 146-158F
The EWTs ran 130-160F. I'm not sure how I got a 160. Possibly an extra long run, or the conductivity of the EWT measurement method was better.

After returning the boiler to 180F set temp the burn time has returned to a single burn averaging about 5 min 21 sec each.
Two were exactly 4min 54sec. One was 6min 15sec. I think someone in the house opened a door to the outside and through that one off.
The flu temp has not changed at around 550F

Of course as the weather gets warmer and the off time between runs gets longer, the EWT will drop again. At least this puts part of the year in a good place for the boiler, and reduces the condensation.
Does anyone here know the BTU/ft of the taller convective radiators? They seem far more capable than baseboard.
I am not using even half of my radiators at 180F so I should have no trouble operating a system at condensing temperatures right up to, and perhaps even during, the next ice age.

I can take more measurements when the weather returns to a more normal 30 something. I'm very happy for the improvements made so far! I can picture the gas company will be out to "update" my meter soon haha!
Thanks!
 

Dana

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There are mod-cons with max output in the 38,000 BTU/hr range or smaller but it's really the minimum output number that is more important than the max when looking at modulating equipment. The Lochinvar CDN040 puts out 37,000 BTU/hr at maximum fire, 8000 BTU/hr @ minimum fire.

But the HTP UFT-080W puts out about twice that much at high fire, but can dial back to an even lower 7600 BTU/hr out at low fire. The Lochninvar KHB-085 also has a lower minimum fire number than the CDN040, and slightly higher output than the UFT-080W. There are others.

Burn times of 5 minutes are fine, knocking a percent or so off the as-used efficiency compared to 10 minute burns (which are pretty close to steady-state efficiency.)

Fin tube convectors come in a wide range of sizes and output per running foot. How deep & tall are the fins? How deep and tall is the sheet metal?
 

JBurdman7

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The Lochinvar Knight WHB055N looks absolutely perfect! It appears that Lochinvar has discontinued the Cadet line. I'm not sure.

The convectors are 6" deep, in a sheet metal box 2ft high, with mostly 2.5" high fins (some units are 3"), with the fins starting 6" off of the floor.
 

Dana

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Those convectors are similar to Modine FL series . See p.13 for the output specs at 190F average water temp. At condensing temperature the output will be about 1/3 those numbers. A 6" deep x 26" tall x 36" wide version puts out 9000 BTU/hr @ 190F AWT, which would be a 3000 BTU/hr per food of width. At condensing temperatures that would be about 1000 BTU/hr per foot.

The Lochinvars are fairly sophisticated mod-cons with lots of bells & whistles which make them both easier and harder to work with. (Easier for setting up complicated multi-temperature multi zoned system, but a lot of programming to optimize a keep-it-simple-stupid kind of system.) They're pretty pricey too. The HTP UFT series are much more stripped down (but far from feature-free) and designed for ease of installation. (Of course the more idiot-proof you make something the more creative the idiots become. :) ). The UFT-080W is substantially less expensive than a WHN-055 too.
 

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Yes that is the design of the convectors.

Even if I maintain the blocking of 13ft of convection located in areas I do not need heated I'd still have 22ft or ~22,000BTU I could distribute before losing condensing efficiency, tho this is worst case because the basement loop will need to dip in to this to warm its additional 18ft.

The 99% design temp for a town in a valley 16 miles West of me is 7 degrees. I'm also 1/3 up the North face of a mountain. If 30,240BTU maintains a 72 degree difference, then 22,000BTU can maintain 51 degree difference. With 72 degrees inside I can maintain condensation mode until outdoor temps go below 21 degrees at worst. During the worst of winter, by the time the water is cooled in the main loop, it might be wise to take that water and instead of returning it to the boiler, run all, or part of it, thru the basement loop first. My 30,240BTU demand estimate includes that trickle given to the basement loop. I think that makes do with about 1/10 the total flow. If I understand correctly any heat over 130 returning to the boiler is effectively lost anyway.

It looks like for me a mod-con system would only be pushed above condensing temps for a few hours per day during the coldest month of the year, and that is only if the basement loop was shut off. On the coldest days it would be a piece of cake to set a small fan at base of a few convectors to make them forced air. I also have a cast iron radiator I spared from a salvage yard which could be added somewhere.
I suppose that there is no such thing as being able to fire to too low of output. Is there a rule of thumb what the suggested minimum fire should be for a 22,000BTU+ distribution system? Seems to me like I would be fine with a 5:1 turn down 45-65,000BTU unit if they exist at a price competitive to the HPT.

I've gone from knowing little about mod-cons to talking like I might know what I'm talking about :) Do you have a PayPal or other sort of "Tip Jar" set up? I owe you. I think you may have taken 20% off my gas bill and added who knows what to the life of my cast iron boiler. Plus if the advice I attach to the unit is followed up on in the future, who knows.

A truck load of thanks to you, sir!
 
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