Radiator EDR/BTU output calcs off by a lot

jesmed1

Another mystery question about our 4-unit 4800 sq ft old condo building in Boston area with old cast iron rads.

Design heating load at 0 degrees outdoor temp is 96,000 BTU/hr. This number is based on actual oil consumption vs. HDD records, and has been confirmed by boiler run times in zero degree weather.

The mystery is that standard radiator output tables seem to vastly over-predict the water supply temperature needed to output 96,000 BTU/hr. Put another way, we're able to heat the building in zero degree weather with much lower water temps than the tables say.

We have about 960 sq ft EDR, which means we need 100 BTU/sq ft output to get that 96,000 BTU/hr output. In practice, on a zero degree day, our two boilers with a total 280MBH DOE output need to run only 96/280=.34 of the time, or about 1/3 of the time.

Because these are cold start boilers that run about 45 minute cycles, that means on a zero degree day, the boilers run 45 minutes, starting with 65 degree water and ending with 140 degree water, for an average water temp of aound 100 degrees. Then the boilers idle for 90 minutes as the water and radiators cool off. So the average water temperature over several hours is 100 degrees or less.

But the radiator tables say that in order to get that 100 BTU/hr output needed on a zero degree days, our water temperature needs to average 145. This is the radiator table I used, and it seems consistent with other tables I've found online:

https://www.expressradiant.ca/pdfs/product_classic_sizing_how_to.pdf

(We have the 9" wide three column radiators.)

But in reality, on a zero degree day, our water temperature is averaging something closer to 110 degrees or less, which the table says should output only 30 BTU/hr. (Yes I realize the BTU output is non-linear with temperature, so using average water temperature will introduce error). But the point is that there's a factor of 2X to 3X error here, and I can't find it. The only error sources I can think of are:

1. Design heating load--I've calculated this 4 different ways, including actual oil consumption, and all different methods agree within 10%. Also, because the boilers run a known time at a known output, I know the actual BTU's being output to the rads on a zero degree day.

2. Radiator sizing and EDR--I've triple checked my radiator measurements and EDR calculations vs the tables. The EDR numbers could be off slightly, but I don't see how they could be off by a factor of 2X or 3X.

3.Radiator BTU output vs. water temp--these numbers given in the radiator tables seem well established and unlikely to be wrong by 2X or 3X.

4. Measured water temps--We have two identical boilers, both with supply water temp gauges, and both agree. Water starts at 65 and ends at 140 on a 45-minute burn. Also, I put surface mount pipe thermometers on the supplies and returns to check delta T, and they confirm that the supply water never gets above 140 and averages much lower.

So the mystery is that the radiator tables say our rads need 145 degree average water temperature to heat the building on a zero degree day, while in reality our average water temperature on a zero degree day is closer to 110, meaning there's an error of 2X to 3X somewhere in our radiator total BTU/hr output for a given water temperature, and I can't find it. Any ideas?

Jamie Hall

Application of precision modern science to the real world. Funny how it doesn't work. There are way too many sources of variation in all those measurements to expect to come up with better than plus or minus 50 percent overall, and when you factor in that at least some of them (the EDR tables and the output tables) are biased strongly to be conservative -- that is if there are unknown factors involved, the result will be conservative and over designed) I'm not a bit surprised at your numbers... the fuel oil vs. heat loss calculation is one of the most suspect, by the way, despite the enthusiasm which some promote it.

To go off on a bit of a tangent. The modern tendency is to design things -- whether it's heating systems, consumer goods, bridges, cars, or what have you -- with much smaller margins of error than were used even 50 years ago. For a set of splendid examples of this, since you are in Boston, go ride the MBTA. Any line. Or read up on the history of the ceilings in the Big Dig tunnels. Or just gaze at the Hancock building...

jesmed1

@Jamie Hall Thanks for your comment. I respect your evident experience and knowledge base, which is why I'm a bit surprised by your view that the fuel oil consumption heat loss calculation is "one of the most suspect."

As a mechanical engineer, my job involves a lot of math and calculating, which is something I enjoy doing. I've also learned how easy it is to be led astray by math errors, bad assumptions, etc, which is why when I went about calculating our design heat loss, I used 4 different methods, expecting to get a wide variety of results.

Honestly, I was surprised by how well the results from different methods agreed. And I trust the oil consumption method most, because it's based on known oil consumption over a period of known HDD's. I double-checked that result by measuring boiler run times during a zero degree day. Both those results are within 10% of each other, which I consider good agreement. And since both are based on actual real-world measurements, to me they seem the most trustworthy.

Even so, the calculated heat loss is somewhat irrelevant to the question at hand, since I know how long the boilers run on a zero degree day, I know the oil gpm input rate and boiler efficiency, so I know how many BTU's are being input to the radiators, and consequently how many BTU's hr they must be outputting.

Back to the original question, I can only conclude that you are correct, that the BTU output numbers given in radiator tables are quite conservative. I did expect some conservatism, but I didn't expect them to be off by a factor of 2 or more.

jesmed1

Here's another though about the source of the error. I did the radiator analysis assuming that the radiators were the only emitters in the building, when, in fact, since this is a converted gravity system, there is a lot of large diameter piping in the basement whose surface areas are also acting as radiators. I had assumed this area was rather negligible, as the common piping pickup factor of 15% implies, but in our case perhaps there is significantly more, and this is effectively adding to the radiator EDR. I still have a hard time believing it accounts for a 2X error, but maybe I'll measure up the pipes and get a ballpark estimate.

hot_rod

I have played around with a few different cast iron radiators at my buildings
Im always amazed how low SWT you can operate at and still get good output

At my last home I had several running  120 SWT on design days!

jesmed1

hot_rod said:

I have played around with a few different cast iron radiators at my buildings
Im always amazed how low SWT you can operate at and still get good output

At my last home I had several running  120 SWT on design days!

@hot_rod This is what I'm finding here. In your opinion are the cast iron radiator tables' BTU output numbers very conservative? Like by a factor of 2?

Jamie Hall

jesmed1 said:

hot_rod said:

I have played around with a few different cast iron radiators at my buildings
Im always amazed how low SWT you can operate at and still get good output

At my last home I had several running  120 SWT on design days!

@hot_rod This is what I'm finding here. In your opinion are the cast iron radiator tables' BTU output numbers very conservative? Like by a factor of 2?

I at least wouldn't be the least bit surprised if they were...

hot_rod

jesmed1 said:

I have played around with a few different cast iron radiators at my buildings
Im always amazed how low SWT you can operate at and still get good output

At my last home I had several running  120 SWT on design days!

@hot_rod This is what I'm finding here. In your opinion are the cast iron radiator tables' BTU output numbers very conservative? Like by a factor of 2?

It wouldn’t surprise me😉

An engineer friend designed a panel radiator system a few years back for an A2whp application. He used the manufacturer derate chart to size them. Under actual load the SWT was able to run 10-12 degrees lower than what the chart indicated. Good news for the heat pumps.

I think load calc numbers based on Manual J are padded by 10- 15%. Then the fudge factors in the heat emitter output chart.

But nothing more frustrating for an HVAC troubleshooter than an undersized or under radiated building, so?

Early in the fin tube design days 200 SWT was common, so not much room for error to increase an underperforming job.

john_james

I think this is the formula. Could someone else verify. dT being the difference in average water vs room temperature.

50 * (dT / 40) ** 1.3


Most of the charts use a linear approximation, being
2 * (T - 95)

That linear approximation predicting zero output at 95F (35C), which you can tell is obviously wrong by standing next to a rad at that temperature.

So your average water temperature of 110F, in a 70F room (dT=40) gives 50Btu/h/sqft or 48kBtu/hr.
a 65F room would be 58Btu/h/sqft or 56kBtu/hr total.

96kBtu/hr would require 100Btu/h/sqft
100 = 50 * (dT / 40) ** 1.3
dT = 40 * 2**(1/1.3)
dT = 68F
T = 138F in 70F room, 133F in 65F room


Other things:
- Did you include boiler efficiency in your heat loss calculation? That could be 15-20%.
- Did you heat loss calculation already include a conservative 30% increase.
- The distribution pipes themselves can act as radiators. Are they insulated in the basement?
- Did the temperature stay at 0 for multiple consecutive days or just one day? If you have a mass brick building or other heavy constructions it can delay the effects.

Hot_water_fan

Remember, the BTU/ sqft EDR charts are published by the very same people who sell the sqft of EDR 

Charitably, they want to make sure you’re always warm. They also get paid based on how many lbs of cast iron they push. 

Love the fuel usage method because it avoids much inevitable guesswork. Let the meter do the work. 

LRCCBJ

jesmed1 said:

Design heating load at 0 degrees outdoor temp is 96,000 BTU/hr. This number is based on actual oil consumption vs. HDD records, and has been confirmed by boiler run times in zero degree weather.

Because these are cold start boilers that run about 45 minute cycles, that means on a zero degree day, the boilers run 45 minutes, starting with 65 degree water and ending with 140 degree water, for an average water temp of aound 100 degrees. Then the boilers idle for 90 minutes as the water and radiators cool off. So the average water temperature over several hours is 100 degrees or less.
somewhere in our radiator total BTU/hr output for a given water temperature, and I can't find it. Any ideas?

This is where you have an error in the calculations. The cold start boiler will climb to your desired 140 degree output temperature much faster than 45 minutes. I would suspect they would climb well above 110 degrees in less than 10 minutes. Additionally, with a 90 minute off time, the boiler will never cool down to 65 degrees. I would suspect that it has not cooled below 85 degrees in that period. So the average water temperature over the 45 minute period is most likely in the range of 130 degrees. You can verify the above by watching a cycle carefully and documenting temperature versus time.

To conclude that years of proper EDR documentation and carefully calculated Manual J data is wildly in error is not correct.

jesmed1

LRCCBJ said:

This is where you have an error in the calculations. The cold start boiler will climb to your desired 140 degree output temperature much faster than 45 minutes. I would suspect they would climb well above 110 degrees in less than 10 minutes. Additionally, with a 90 minute off time, the boiler will never cool down to 65 degrees. I would suspect that it has not cooled below 85 degrees in that period. So the average water temperature over the 45 minute period is most likely in the range of 130 degrees. You can verify the above by watching a cycle carefully and documenting temperature versus time.

To conclude that years of proper EDR documentation and carefully calculated Manual J data is wildly in error is not correct.

OK, thank you for thinking this through. Because we have so much thermal mass (140 gallons water = 1166 lbs, plus 4000 lbs of cast iron radiator, per 140MBH boiler), the supply water temp increases very slowly. But I have watched the temp rise vs. time over the years, and I can know how long the boiler has been running just by looking at the boiler temp gauge during a cycle. 120F means it's been running for about 20 minutes, 130 means 30 minutes, 40 means it's been running about 40 minutes.

So the time-average water temperature during a 40-minute run is about 120 degrees. And then there's a longer cooling period during which the average is definitely lower than 120. So I'm confident in saying that, on a zero-degree day, the average water temperature over a number of on-off cycles is still under 120 degrees. According to the radiator charts, that's 50 BTU/hr/sq ft, which for our total radiator EDR is only about half the rate at which the building is losing heat on a zero-degree day. So there's still a big 2x factor missing.

I'm not saying the radiator tables are wrong, but I am saying that there is still a multiple of 2 error somewhere that I cannot find.

jesmed1

Hot_water_fan said:

They also get paid based on how many lbs of cast iron they push.

Let's think this through. If I want to sell more radiators, then I should under-predict how many BTU's they radiate, because the customer has a heat loss number of, say, 100,000 BTU/hr that he wants to satisfy with X radiators. And the fewer BTU's each radiator gives off, the more radiators he needs to buy.

So the radiator seller would under-predict the BTU's per sq ft for a given water supply temperature. Let's say he knows the radiator will provide 100 BTU's per sq ft EDR at 120 degrees, but he advertises 50 BTU's per sq ft EDR at 120 degrees.

I'm not sure if that would be a good business strategy, but if that's what's happening, it could explain my observations here, because our radiators seem to be radiating at double the advertised BTU.

However, as @LRCCBJ says, I don't think it's possible that so many years of careful EDR observation are so wildly in error.

jesmed1

john_james said:

96kBtu/hr would require 100Btu/h/sqft
100 = 50 * (dT / 40) ** 1.3
dT = 40 * 2**(1/1.3)
dT = 68F
T = 138F in 70F room, 133F in 65F room

@john_james That's close to the radiator table which says 145F gives off 100 BTU/hr/sq ft, but it is 7-12 degrees lower, which is closer to my observed lower water temps. So it looks like your formula and calculations are correct.

To address your other points:

-Yes, I factored in the boiler measured 85% efficiency.

-The heat loss calculation has been done 4 different ways and all agree within 10%. But to some extent the building heat loss is irrelevant, because I know the actual BTU/hr output of the boilers, and this known BTU quantity is being radiated away by the radiators. The discrepancy is that the radiators are radiating these BTU's away at a much higher rate than the tables say they should for a given water temp.

-The basement pipes are not insulated, so they will add some radiation surface area. I've conservatively estimated their surface area at about 25% of the radiator EDR. So that will account for some error, but not a factor of 2.

-Re the building thermal mass and heat loss, again the building heat loss is somewhat irrelevant. What matters is how many BTUs/hr the boiler outputs, and how long it runs, both of which are knowns. That known BTU output is being rejected by the radiators and distribution pipes, at a rate which seems to be much higher than the radiator tables predict.

Jamie Hall

May I point out a logical flaw in the assumption that heating installers and engineers and suppliers will over design, so they get paid more? This may be true to a small extent -- but to a much greater extent, most engineers and other such folk will over design to varying degrees based on a simple observation: it is very rare for the client to get annoyed if the project works as intended, but they tend to get upset when the product doesn't.

How big the over design is varies widely. If the inevitable cascade of variation in a job results in mild annoyance, not all that much. If it results in someone dying, perhaps more...

john_james

jesmed1 said:

john_james said:

96kBtu/hr would require 100Btu/h/sqft
100 = 50 * (dT / 40) ** 1.3
dT = 40 * 2**(1/1.3)
dT = 68F
T = 138F in 70F room, 133F in 65F room

@john_james That's close to the radiator table which says 145F gives off 100 BTU/hr/sq ft, but it is 7-12 degrees lower, which is closer to my observed lower water temps. So it looks like your formula and calculations are correct.

To address your other points:

-Yes, I factored in the boiler measured 85% efficiency.

-The heat loss calculation has been done 4 different ways and all agree within 10%. But to some extent the building heat loss is irrelevant, because I know the actual BTU/hr output of the boilers, and this known BTU quantity is being radiated away by the radiators. The discrepancy is that the radiators are radiating these BTU's away at a much higher rate than the tables say they should for a given water temp.

-The basement pipes are not insulated, so they will add some radiation surface area. I've conservatively estimated their surface area at about 25% of the radiator EDR. So that will account for some error, but not a factor of 2.

-Re the building thermal mass and heat loss, again the building heat loss is somewhat irrelevant. What matters is how many BTUs/hr the boiler outputs, and how long it runs, both of which are knowns. That known BTU output is being rejected by the radiators and distribution pipes, at a rate which seems to be much higher than the radiator tables predict.

Yeah you're right, the heat loss should be irrelevant if you are going off the boiler output.

If you want a good estimate of heat loss from the pipes:

https://www.engineeringtoolbox.com/steel-pipes-heat-loss-d_53.html

Be careful, it defaults to metric and apply the correction factors at the bottom of the page. If your basement is 55F a 3" supply pipe at 145F could be losing up to 10kBtu/hr per 100ft.

Hot_water_fan

Ha @Jamie Hall nobody is dying if their system is only 1.4x oversized vs 2x. These are just normal people. They make mistakes and they also respond to the same incentives we all do. 

EBEBRATT-Ed

@jesmed1

Just wondering how you are figuring the boiler input/output. Taking the oil consumption and dividing it out by hours is one way.

Or go by nozzle size. I have in the past wired an hour timer (Grainger and others have them) in parallel with the burner motor to get actual run hours. Then knowing the nozzle size (and you have to factor in oil pump pressure if not 100psi) hours x firing rate x boiler efficiency would be the most accurate.

Also, when the boilers shut down does the circulator also stop. I have used a strap on aqustat to keep the circ on until the water falls to 120 to extract the heat from the boiler and piping and put it up into the
space. Your probably already at low water temp so that may not be of any use.

I also use that hour meter to determine an underground oil tank was leaking. The customer complained that her oil deliveries were higher than in the past. The hour meter calculation showed the oil actually burned and sticking the oil tank proved that that they were using more oil than that.

LRCCBJ

jesmed1 said:

LRCCBJ said:

This is where you have an error in the calculations. The cold start boiler will climb to your desired 140 degree output temperature much faster than 45 minutes. I would suspect they would climb well above 110 degrees in less than 10 minutes. Additionally, with a 90 minute off time, the boiler will never cool down to 65 degrees. I would suspect that it has not cooled below 85 degrees in that period. So the average water temperature over the 45 minute period is most likely in the range of 130 degrees. You can verify the above by watching a cycle carefully and documenting temperature versus time.

To conclude that years of proper EDR documentation and carefully calculated Manual J data is wildly in error is not correct.

OK, thank you for thinking this through. Because we have so much thermal mass (140 gallons water = 1166 lbs, plus 4000 lbs of cast iron radiator, per 140MBH boiler), the supply water temp increases very slowly. But I have watched the temp rise vs. time over the years, and I can know how long the boiler has been running just by looking at the boiler temp gauge during a cycle. 120F means it's been running for about 20 minutes, 130 means 30 minutes, 40 means it's been running about 40 minutes.

So the time-average water temperature during a 40-minute run is about 120 degrees. And then there's a longer cooling period during which the average is definitely lower than 120. So I'm confident in saying that, on a zero-degree day, the average water temperature over a number of on-off cycles is still under 120 degrees. According to the radiator charts, that's 50 BTU/hr/sq ft, which for our total radiator EDR is only about half the rate at which the building is losing heat on a zero-degree day. So there's still a big 2x factor missing.

I'm not saying the radiator tables are wrong, but I am saying that there is still a multiple of 2 error somewhere that I cannot find.

jesmed1 said:

LRCCBJ said:

This is where you have an error in the calculations. The cold start boiler will climb to your desired 140 degree output temperature much faster than 45 minutes. I would suspect they would climb well above 110 degrees in less than 10 minutes. Additionally, with a 90 minute off time, the boiler will never cool down to 65 degrees. I would suspect that it has not cooled below 85 degrees in that period. So the average water temperature over the 45 minute period is most likely in the range of 130 degrees. You can verify the above by watching a cycle carefully and documenting temperature versus time.

To conclude that years of proper EDR documentation and carefully calculated Manual J data is wildly in error is not correct.

OK, thank you for thinking this through. Because we have so much thermal mass (140 gallons water = 1166 lbs, plus 4000 lbs of cast iron radiator, per 140MBH boiler), the supply water temp increases very slowly. But I have watched the temp rise vs. time over the years, and I can know how long the boiler has been running just by looking at the boiler temp gauge during a cycle. 120F means it's been running for about 20 minutes, 130 means 30 minutes, 40 means it's been running about 40 minutes.

So the time-average water temperature during a 40-minute run is about 120 degrees. And then there's a longer cooling period during which the average is definitely lower than 120. So I'm confident in saying that, on a zero-degree day, the average water temperature over a number of on-off cycles is still under 120 degrees. According to the radiator charts, that's 50 BTU/hr/sq ft, which for our total radiator EDR is only about half the rate at which the building is losing heat on a zero-degree day. So there's still a big 2x factor missing.

I'm not saying the radiator tables are wrong, but I am saying that there is still a multiple of 2 error somewhere that I cannot find.

You have done your homework. I accept the conclusion that your AWT is somewhere near 120F.

You mentioned that your 96K heatloss at 0 degrees is based upon fuel consumption. What is generally missing from this calculation is the system efficiency. Most folks simply calculate the system efficiency as the energy provided by the fuel (140K BTU/gallon for oil) multiplied by the boiler's stated efficiency (say 82%). This provides their conclusion for the heatloss of the building when multiplied by the boiler operating time over a quantifiable period.

Let me give some anecdotal evidence how the system efficiency can be wildly different:

I had a house that utilized 132M BTU of oil over a calendar year. It never varied much over the course of 15 years. I finally decided that I would install a large HWH with a heat exchanger and see if I could heat the building (all CI) with the 142 degree output temperature. The results proved that I could be successful 95% of the time. If the outdoor temperature dropped below 10F, the building would fall slightly in temperature. This was because the HWH would shutdown at limit, eventually, because the CI could not accept the full output of the HWH (estimated to be 50K) over and extended run time (several hours).

The reason I mention this story is the fact that the total fuel consumed by the HWH over a calendar year was 77M BTU.

This is with a boiler that could manage 77% efficiency when measured and a HWH that certainly did no better than 64% efficiency.

The system losses in most buildings (and in every building with a CI boiler in an unheated basement) are astounding.

My personal belief is that the CI boiler dumps 10K per hour for every hour it runs and NONE of that energy is recovered by the building (the basement is unfinished and cooler than the first floor). Furthermore the "inefficient" HWH is fully wrapped (from the factory) with 2" of foam insulation.

In your situation, you might find that 20-30% of the fuel is simply wasted and your actual heatloss is significantly less than the calculated 96K.

jesmed1

@john_james Thanks for the pipe BTU tables. I'll factor those in and see what happens.

@EBEBRATT-Ed. We have 1.0 nozzles at 140 psi, so 1.18 gph input. I time boiler runs with a data logger set on the boiler near the flue pipe. The data logger records the temp spikes as temp vs time from the boiler runs. I have a phone app that downloads the data via Bluetooth and shows it on a graph. So I can see each boiler run as a temp spike, when it started, and when it peaked at boiler shutdown. That gives me boiler runtime with 1-minute accuracy, which is good enough.

I've collected hundreds of hours of runtime data over years, especially in previous years when we had problems not getting enough heat in upstairs units. The data loggers helped me identify and fix short cycling problems, and also to measure total run times for different outdoor temps.

That run time data has helped verify heat loss calcs, and ultimately led to the observation that kicked off this thread, ie that even on a design day, our avg water temps are nowhere near what the radiator tables say is needed.

jesmed1

@LRCCBJ Thank you, and there's a lot of food for thought in your post. I'm especially interested in your HWH experiment and your oil consumption drop from 132 million BTU to 77 million BTU. That is a massive 42% savings. We burn nearly $5k a year in oil, so a 42% savings would mean around a $2k savings per year for us, which would be significant.

We could do something similar even more effectively, because as I keep repeating, we only need average water temps below 120 to heat the entire building on a design day, where you needed 140+.

I actually looked into getting a giant ATW heat pump running a buffer tank heat exchanger tied into our existing cast iron radiator system, but the up front cost was too steep. But the technical aspect could have worked, because we don't need very hot water. We only need maybe 110-120 degree water at most.

Can you please explain your HWH setup in more detail? Because if we could do that here, I'd be very interested. If it's too detailed, maybe you could PM me.

Now, on to your points about (1) actual boiler efficiency and (2) actual building heat loss. I've seen arguments on both sides of the cast iron boiler efficiency question, and I haven't done enough research to know who's right. I am prepared to believe that our actual efficiency is less the 85% combustion efficiency measurement we just got done. How much less, and why, is the subject of much debate that's been covered elsewhere, including here:

https://forum.heatinghelp.com/discussion/162380/is-it-possible-to-test-a-boiler-efficiency/p1

I'm going to read that thread and see if I can understand @captainco 's argument that a CI boiler is really only about 65% efficient instead of 85%. Even in that thread, some pros disagreed with him.

As for the building heat loss, I calculated that manually as well, and got numbers in the 80,000 BTU/hr range. That's about 15% lower than the 96,000 BTU/hr number from fuel usage. But it's also based on unverified assumptions about construction materials and methods in this 1920's house, so I was reluctant to give it too much weight. Also, 80,000 BTU/hr divided by 4800 sq ft = 17 BTU/hr/sq ft. which is a rather shockingly low number for a 100-year-old house with many original double-hung windows (which have been professionally weatherstripped) and weighted flue dampers in the basement that flap in the breeze when the arctic winds blow, sucking warm air right up the chimney.

So I am actually more inclined to believe the 96,000 BTU/hr heat loss number from oil consumption, if only because that gives us 20 BTU/hr/sq foot, which seems more believable to me for this old house. From what I've read, 20 BTU/hr/sq ft is decent for new construction around here, and I still have a hard time believing we're as good as that.

In any case, I'm most interested in your HWH experiment and your proven efficiency gain, so I'd appreciate it if you could give me more details, maybe via PM.

Hot_water_fan

But it's also based on unverified assumptions about construction materials and methods in this 1920's house, so I was reluctant to give it too much weight. 

Bingo - unless you observe the construction and get a blower door, it’s a guess. And things change! A house can become leakier. 

What’s the exact brand of radiator you have?

jesmed1

Hot_water_fan said:

And things change! A house can become leakier. What’s the exact brand of radiator you have?

@Hot_water_fan LOL. Hopefully it's become less leaky with all the work I've done on it!

Here's one of our radiators. 9" deep, 3 column, marked "USRCORP."

EBEBRATT-Ed

@jesmed1
some of the difference between you fuel burned and the actual heat loss of the building is heat lost up the flue as you mentioned in your other post and also the "piping and pick up "factor for hot water usually 15%

jesmed1

EBEBRATT-Ed said:

@jesmed1
some of the difference between you fuel burned and the actual heat loss of the building is heat lost up the flue as you mentioned in your other post and also the "piping and pick up "factor for hot water usually 15%

Thanks, yes, I was ignoring that as "small potatoes" relative to the seemingly large discrepancy in water temperature, but I think I'm realizing that there are a number of "small potatoes" that may add up to bigger potatoes. Like the 7% latent heat loss I didn't know about, the pick-up factor which could be larger than 15% since we have so much large-diameter pipe in the basement, etc.

I'm going to try to add all those little potatoes up and see what happens.