Calculating basement/pickup losses
I’m trying to quantify the losses from my steam boiler, it’s in a cold basement, currently leaking steam up the chimney, and doesn’t have a powered flue damper. It’s been tested at 82.5% efficiency, it’s also being replaced in a couple weeks so while it’s cold I’ve been looking in to the duty cycles a bit.
Assuming the basement losses are completely lost, is it roughly the time it takes for the steam main vents to close?
So if it runs for 25 minutes, is off 120 minutes, and takes 7 minutes to get steam to the end of the mains, that’s a 28% loss factor at that temperature cycle. Actual BTUs/hr in to the living space would be 192,000 input * .825 * (25/120) * .28?
Comments
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The boiler is constantly losing energy to the environment. With the CI at 212F and the basement at 50F, the losses are significant. I did a calculation once for a HW boiler and the loss was about 8K. Your steam boiler could be twice this value considering its temperature and size.
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Just because the basement is out of sight doesn't mean that heat delivered to it is "lost". Far from it. It prevents heat from escaping down (which it otherwise would) from the first floor. Without it your first floor floors would be cold.
Unless the basement is very draughty, you are not losing heat from the boiler or the piping — it's just heating the basement.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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Unfortunately, incorrect.
Almost all the heat from the boiler goes right out of the basement through the cement block walls that are above ground and below the sill plate. With an R value of .8 it would much rather head outdoors than attempt to penetrate the first floor (probably an R value of 3).
Of course, YMMV if you have a fully insulated basement. Then some of it is recovered.
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I'd tend to agree with Jamie that due to the tendency of hot air to want to rise the ratio getting to your feet on the first floor might be higher than those R values. I know after insulating all my piping I noticed the difference in colder floors. Considering removing some of what I had put on years ago, at least on all the returns. Softwood also has an R value of only 1.5 and hardwood 0.5 and that is if it is solid.
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And you are assuming that all basements are cement block (one thickness) and elevated somewhat above the ground… which isn't true. Don't make assumptions. (The foundation walls for Cedric's home are about a foot clear of the ground — and between two and three feet thick, stone…). And the first floor is leaky…
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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Clearly, you have what I would refer to as a 1% building. Of course, for that building, you are correct.
One makes assumptions about everything since the data is not typically available.
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I did give the disclaimer of basement losses are lost, as my basement is block with 50% above grade and 8 decent sized windows.
Part of this exercise is to see how much my minisplit is contributing to my house load. When running with the split my boiler cycles are off for almost 3.5-4 hours, vs 2 hrs when it’s only the boiler at the same outdoor temp.0 -
That's only the heat lost from the piping when the boiler is off.
Do NOT oversize the boiler because of this.
How much radiation do you have installed?How long does the current boiler run on the coldest days? Does it build excessive pressure? (anything over 1/4 PSI in my opinion).
Is this natural gas or oil?
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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It's massively oversized at 192k input natural gas, 1968. It builds pressure with a setback of more than 1-2 degrees. We are ~ EDR of 310 now, replacement will be an EG-40 with vaporstat.
At -20F it was running a ~50% duty cycle, lol.
7 minutes to main vents to close on a 25 minute cycle.
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If you size it right you won't need a vaporstat I promise.
I'm using an EG-40 with 392sqft.
For you Id go with an EG-35.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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Pickup factor grossly overstated?
End of the day it's all based on the heatloss, I can't imagine there being much of a difference between the two sizes hooked up to the same system?
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The 30 and 35 are the same boiler with minor changes.
The 40 and 45 are also the same. Mine started as a 45 and I didn't like it. It behaves much much nicer as a 40 on my system because it never builds pressure. It's silent all of the time.
If I had your house id be tempted to try the EG30 but I feel the 35 is the safer bet.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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It's not based on heat loss, it's based on the amount of steam that your radiators can condense. And yes, pickup factor is grossly overstated
NJ Steam Homeowner.
Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
See my sight glass boiler videos: https://bit.ly/3sZW1el0 -
If you have an oversized radiator that heats halfway, or a rightsized radiator that heats fully across, isn't it fullfilling the same X BTUs/hr that your room is calling for?
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Yes, but that's not the question to ask.
If you have a boiler that makes X amount of steam per minute, and you have total radiation that can only condense 80% of that (for example), you will unnecessarily build steam pressure wasting fuel and causing issues with your system.
So you size a boiler with the home's total radiation as the primary input variable.
NJ Steam Homeowner.
Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
See my sight glass boiler videos: https://bit.ly/3sZW1el0 -
So you size a boiler with the home's total radiation as the primary input variable.
He makes an interesting point Paul. If he sizes the boiler to 80% of the radiation and the rads never completely fill (thereby never making any pressure to shut the boiler down) and the building has more than sufficient BTU's at design…………..
Dave has discussed this endlessly and has followed this approach on two pipe systems without any issues.
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That's fine, you can take advantage of the ridiculous pickup factor of 33% extra size in order to go to a smaller boiler, no problem there.
I thought he was saying there was no difference between hooking up two different sized boilers to the same sized system, including an oversized one.
NJ Steam Homeowner.
Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
See my sight glass boiler videos: https://bit.ly/3sZW1el0 -
I believe he was thinking that there is no good reason to fully fill an oversized radiator…………why not fill it half way and call it a day?
It goes contrary to the usual logic of the necessity to completely fill every radiator on every boiler cycle.
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You definitely don't have to explain it again, I have no problem undersizing a boiler compared to the industry norm of 33% oversized.
NJ Steam Homeowner.
Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
See my sight glass boiler videos: https://bit.ly/3sZW1el0 -
As long as you know the house... My house is a bit under radiated downstairs because of an added sunroom and some radiator swapping/eliminating done sometime in the past. I have to keep my kitchen radiator nearly filling every cycle to avoid the room just being cold even in normal winter temperatures.
There may also not be any insulation on mains or even some takeoffs in some houses. Then the pipes are no different than radiators in the EDR total except they may condense more if in cold drafty areas. I agree in most cases you should be able to go less than 33% but it would be better to see the house and better still to live in it before confidently suggesting someone go 0% or less.
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I would respectfully disagree with you. It doesn't matter if your house is under-radiated. The radiation that is in there IS WHAT IT IS and can only condense X amount of steam per minute. If the boiler is sized above that, you will just be building unnecessary wasteful pressure.
Please don't put words in my mouth, I have never suggested anyone go with 0% or less than 0% of pickup factor. I have only said that 33% is ridiculously, unnecessarily high for any home.
NJ Steam Homeowner.
Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
See my sight glass boiler videos: https://bit.ly/3sZW1el0 -
If the radiators can only dissipate X amount of heat at a given ambient temperature, how exactly does going beyond that with the boiler output increase their output? Installing a bigger boiler does not help with too little radiation unless you're attempting to build pressure hoping to run those radiators hotter.
It's my opinion that properly sizing a steam boiler is both art and science. I personally disagree with just going by the installed EDR and throwing an extra 33% on top of it, and then more often than not rounding up to the next bigger boiler because the closest one is only 25% over. That's why I asked the OP how the current boiler behaves etc.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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@ethicalpaul I was not commenting directly "at" you and I know we are generally on the same page on sizing and other matters. I eagerly read all your posts. My only generic point was that some homes balancing needs may be more difficult than others with a boiler that is just sized near 1:1 with the standing radiation and that piping losses can also vary significantly home to home. In one's own home you can get much more aggressive than in recommendations to another's.
I was curious to see what the piping losses indeed could be in my own house with a worst case assumption of uninsulated pipes (they aren't). So, I measured all the sizes and lengths of the mains (previously done) and all the takeoffs to the radiators (some lengths admittedly estimates) and came up with 151sqft of radiation. That would be 28% on top of my 531sqft of standing radiation. Curious to know what some of the other folks quantity of piping is relative to their radiators. I suspect many might indeed be less than mine.
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Your piping uninsulated would only be 28% over your installed radiation, and yet it is insulated so why use 33% even in your scenario?
Curious, what are your piping losses with the insulation? @KC_Jones could maybe help, I think he figured out the numbers per foot of piping with and without insulation.I'll get back to you with my numbers, I used to know them but need to do some digging. It wasn't terrible without insulation but with the 1" insulation it was something small like 3,000 btu/h.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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Again I am in total agreement that normally 33% is way too much so hopefully that is not being misinterpreted. Just there are some scenarios where closer may be more appropriate and we don't always know all the facts about any one given application.
Look forward to seeing yours numbers @ChrisJ and others!
There area other variables on supply piping like average ambient temperature where it resides vs the radiators that are in fully heated spaces. Most homes have some semblance of a basement where that is maybe only 10 degrees or so difference but others including some older commercial buildings where most of the piping is basically in crawl space.
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My basement runs in the high 50s when it's cold out.
My crawlspace(s) run mid 30s. I've actually had frost on a floor a few times. That scenario should have improved quite a bit since I did some changes to keep the space less drafty. All of these areas were much warmer before I insulated my steam piping.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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Thanks @dabrakeman I agree we are all on the same page 🙂
I do really hate supply pipes that are in cold spaces and agree that they can pull a lot of heat away from the steam. When I re-ran one of my upstair supplies due to a sag that was impossible to deal with in the basement, it felt SO GOOD to have that riser in the living space knowing that 1. it was losing way less heat vs being in the unconditioned drafty stud bay and 2. any heat that it did lose went into my living space.
My wife wasn't nearly as thrilled, but I found that all my upstairs risers in fact used to be in the living space but were moved to the exterior walls some decades ago (I could tell due to plugs in the first floor planks).
NJ Steam Homeowner.
Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
See my sight glass boiler videos: https://bit.ly/3sZW1el0 -
"Your piping uninsulated would only be 28% over your installed radiation, and yet it is insulated so why use 33% even in your scenario?"
I am also not saying that my situation would warrant a 33% pickup. I'd have probably gone with an EG-50 in my case but instead was stuck with a EG-65 before learning much about steam… . The 16% below the standard 33%PU sizing though would be on the cusp of what I would recommend to anyone else not knowing all the details of their system.
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.622 sq ft of EDR per foot of 2" main. And that is if it's uninsulated. If insulated, once the main is hot it's basically out of the equation. See screenshot below of a chart I made to visualize how much 2" main it would be if it was uninsulated and being used as radiation. I also have columns showing 1 1/2", 1 1/4" , and 1" pipe if anyone was interested.
Also, the EDR has nothing to do with initial heating of the main. The main heating is a function of the specific heat of steel so it's a different set of calculations. I haven't done it for a while so I'm rusty, anyone else is free to do it. What I do recall is it was minimal amount of energy to warm the mains and typically equated, time wise, to how long my main took to heat when completely cold.
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The only caution is that you need to make sure the radiators fill an equal amount at the same time otherwise a radiator can fill completely before another radiator fills and if you have intentionally undersized that second radiator might not be able to heat because the other radiators are consuming all of the output of the boiler. It is easer to balance this with 2 pipe than one pipe where the main venting and radiator vents are your only way to control balance.
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Keep in mind.
A totally closed radiator vent will cause a radiator to not heat at all, especially when pressures are very low. While a D will cause it to vent very fast. This means you've got everything from nothing to fast at your disposal. That's a lot of control.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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My bedroom radiators get hot late if at all by choice. As mentioned earlier the kitchen radiator goes quick, but again by choice. Both based on the comfort levels in the rooms. When weather gets really cold the cycles are longer and the bedroom radiators heat more sections. Works out very well. With an aggressively undersized boiler I'm not sure I would be able to set up this unique balance as easily without constantly fiddling with the vent rates throughout the house as the weather fluctuates.
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Why do you feel having a smaller boiler would change anything at all?
@KC_Jones Did you notice any difference in your balancing when you changed things? I certainly didn't going from an EG-45 to an EG-40. I didn't change any of my vents that I can recall.
Producing more steam than your radiators can condense isn't going to fill radiators any more than producing just enough to fill them. Let's be fair here, we're talking about properly sizing a boiler rather than oversizing it. You're not going to be lacking steam. No one is recommending undersizing anything.
Something else I can add to this is I have TRVs on 5 out of 10 radiators. Whether those 5 are completely off, or all 10 radiators are on everything works fine and stays balanced. There's no steam hogging and I've been running the system like this for many years now. It's consistent and predictable. I thought the TRVs would cause issues but they never did. I added two of them to hold back two grossly oversized radiators in bedrooms and then the other 3 are just to deal with heating from the sun, cooking etc.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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I changed nothing on the venting, and the balance was still fine.
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If you look at a heating cycle as a block of time more steam being produced will influence how much steam gets to a radiator in that block of time. It also does not require a higher pressure because that can to a degree be offset by faster venting. Condensation rates of course also will be way higher during system cold startup. Again, I have a rather peculiar balance setup because of the non original layout of the radiators combined with personal taste for temperature disparity within the house. All I am saying is with a barely large enough system for an evenly balanced system to fill that kitchen radiator in the same amount of time I currently do less steam will be going elsewhere.
Also whether radiators are on or off can indeed impact balance significantly at least in my case. There are two radiators on a 2nd floor riser to two bedrooms in my house. If one of those two radiators is shut off the other radiator gets much less steam during a cycle than it does when both are on. Been monitoring this for 22 years so pretty confident :)
To be fair it has mentioned numerous times by a few here that (paraphrasing) they are at least tempted to size only to the standing radiation with no PU since radiators are too large for the homes now anyway and never need to be filled… i.e. EG30 with 310sqft radiation. My only point from the beginning is that this may be appropriate for one who is steam savvy in their own home but be careful when recommending it to others.
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Of course one radiator will get less steam, you greatly reduced the amount of venting on that riser by turning off one of two radiators.
The solution is to vent the riser separate from the two radiators. Use a Gorton 6 on the riser and then a 4 or 5 on each radiator.
Single pipe 392sqft system with an EG-40 rated for 325sqft and it's silent and balanced at all times.
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Yes be careful, just like the contractors who put in a new boiler that is one size bigger while being totally ignorant that the existing one is already oversized. Definitely be careful.
I don't think anyone is telling people to ignore pick-up factor, but it seems like you keep thinking we are.
What I've seen is people advocating that homeowners be aware of the EDR of their system, then make a reasonable decision based on that.
NJ Steam Homeowner.
Free NJ and remote steam advice: https://heatinghelp.com/find-a-contractor/detail/new-jersey-steam-help/
See my sight glass boiler videos: https://bit.ly/3sZW1el1 -
Agree that would be better but right now I just have to adjust the Ventrite 1 on my bedroom radiator from 6 to 3 on the rare occasion that the other bedroom radiator is on, so have not ripped up the floor in the closet between them to evaluate putting in a vent there. Laziness mostly…
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You can put it before the radiator valve, don't need to get in to the floor.
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