New Gas (steam) Boiler Install Questions

PiperPete

Just curious before my boiler gets installed; I've got 2 questions:

1) Is there any way to determine if a particular size is too small after it's installed and put into service? Would a size too small affect the time it takes to heat the rooms? For example, my Weil-McClain would heat up to the desired temp. within 15 to 20 minutes of the thermostat calling for heat; Is that within "normal" performance? Is taking longer than 15 to 20 minutes considered a sign of an undersized boiler or some other issue?

2) And what about a boiler that is "oversized"? How does one know a boiler is oversized after it's in installed and put into service? Does it heat the space too quickly? Or are there other concerns with an oversized boiler?

Since my current boiler is considered "oversized" (according to 2 contractors) I'm more concerned about an undersized boiler install so question one is more important to me.

Thanks all.

mattmia2

Significantly too small and it won't heat all the radiators.(although many other problems can also cause this)

It is too big if the pressuretrol shuts the boiler off before the thermostat is satisfied. If the boiler perfectly matches the emitters connected to it, it will never build any pressure.

PiperPete

mattmia2 said:

Significantly too small and it won't heat all the radiators.(although many other problems can also cause this)

It is too big if the pressuretrol shuts the boiler off before the thermostat is satisfied. If the boiler perfectly matches the emitters connected to it, it will never build any pressure.

Thanks mattmia2:

So assuming it does heat all the radiators but takes longer than 15 to 20 minutes to satisfy the thermostat, would that be an indication the boiler is undersized or some other issue?

Jamie Hall

You have to remember that the while the boiler supplies heat to the radiators, it is the radiators that heat the room. As @mattmia2 said, if the boiler is significantly undersized it won't heat all the radiators. However, if it does heat all the radiators, it is at least sized adequately, though it may still be oversized.

That said, if all the radiators heat, how long it takes to satisfy the thermostat has nothing at all to do with the boiler size. That will be controlled entirely by the radiator size and the room heat demand.

KC_Jones

PiperPete said:

Significantly too small and it won't heat all the radiators.(although many other problems can also cause this) It is too big if the pressuretrol shuts the boiler off before the thermostat is satisfied. If the boiler perfectly matches the emitters connected to it, it will never build any pressure.

Thanks mattmia2: So assuming it does heat all the radiators but takes longer than 15 to 20 minutes to satisfy the thermostat, would that be an indication the boiler is undersized or some other issue?

You really need to get off the time thing, it’s essentially a meaningless metric.  The reality is the longer it takes the better for efficiency and comfort.  If you can satisfy the thermostat in 15 minutes when it’s really cold out, or close to design, then the system is oversized for the house, and the boiler was sized to that system.

I have a fairly rare properly sized steam system, so on the coldest days my rads stay fully hot for days on end in some cases.  Boiler running for 50 minutes out of 60.  This is when my house is the most comfortable. 

PiperPete

To KC_Jones:

You say: "You really need to get off the time thing, it’s essentially a meaningless metric."

Let me put the question this way:

First, I'm defining a cold-start as all radiators are cold when the boiler is initially turned on.

Let's say the boiler is to be replaced but currently it satisfies the thermostat in 15 minutes from a cold start.

Then when the boiler is replaced, it takes 1 hour to satisfy the thermostat (same temp setting as before) from a cold start.

You're saying that the timing is "essentially a meaningless metric".

As I view it, the new boiler has to run 45 minutes longer to meet the thermostat, so during that additional 45 minutes it's using more gas than the boiler it replaced.

So from a cost savings, where is the operating efficiency (not boiler efficiency) if it takes 45 more minutes to meet the thermostat?

From a convenience point, would anyone want to have to wait 1 hour to get up to temperature on a cold January day?

Now I do realize that if the boiler is kept on during cold Winter months, which is typical, it will take less time to satisfy the thermostat because the radiators will likely never be cold, hence the room temp. will be closer to the thermostat setting and so take less time to satisfy the thermostat.

Bottom line though, is there a metric for a residential setting that says to the effect that if the thermostat is not satisfied in a "reasonable" period then that needs to be looked into?

My inquiry really boils down to what is a "reasonable" period of time to wait in order to satisfy the thermostat?

Jamie Hall

Go back and reread my comment above. And then read it again. I said that assuming that all the radiators do get hot, then how long it takes for the house to meet the setpoint has nothing to do with how big or little the boiler is.

Where there is a variable which might have something to do with the boiler size is how long the boiler itself takes to heat up from a cold start -- a heavier boiler will take longer -- and how well insulated, if at all, the boiler piping and supply mains are. Uninsulated mains and piping will take considerably longer to supply heat to the radiators than insulated ones will.

The only useful metric on time is how long it takes for steam -- since that is what I think we are talking about -- to reach the radiators once steam is raised in the boiler, not from when the burner starts.

Now some folks might want to have heat appear in minutes from turning up the thermostat. That's fine, but for that you need forced hot air, not hot water or steam.

In contemplating time and nothing else, you are also not taking into account the firing rate of your boiler. Is the new boiler firing at the same rate as the old? Then yes, running longer will take more fuel. If not, then not necessarily.

ChrisJ

@Jamie Hall

All of my radiators can get fully hot.
But using the smaller boiler they obviously take longer to produce X amount of output so the house takes longer to heat than it did with the larger boiler.

To me this is a benefit because it's easier to control and makes things less noticeable 

PiperPete

To Jamie Hall:

I did read your comment that as long as all radiators get hot, meeting the setpoint has nothing to do with how big or how small the boiler is.

Understood.


So, I'll ask you to re-read what I asked at the bottom of my last post:

----
"Bottom line though, is there a metric for a residential setting that says to the effect that, if the thermostat is not satisfied in a "reasonable" period then that needs to be looked into.

"My inquiry really boils down to what is a "reasonable" period of time to wait in order to satisfy the thermostat?
----

There has to be a "reasonable" period of time between when the the thermostat is satisfied otherwise the point of using a thermostat would seem meaningless and could be replaced by a manual switch. If a boiler "A" takes 1 hour to meet the thermostat, then you'd have to set the thermostat 1 hour earlier to do so. If boiler "B" meets it within 15 ~ 20 minutes, then I'd say that's "reasonable".

Interestingly, there is a post on the topic from this forum:

Mad_dog provides his answer...

https://forum.heatinghelp.com/discussion/66850/how-long-should-it-take-for-a-steam-heat-boiler

To me, 20 minutes, worst-case seems like a "reasonable" expectation, though I'd prefer 15 minutes.

So to reiterate, this is a two-part question: I'm asking a) what is a "reasonable" amount of time - if there is such a thing - to meet the thermostat, and secondly, b) is there an industry metric on what is considered to be a "reasonable" amount of time to meet the thermostat..

Thanks!

mattmia2

A perfect system would never shut off, it would add just as much heat as the building is losing.

The amount of heat your system can output was set by the people who sized and installed the radiators around a century ago. Usually this is more than the amount of heat your house loses on the worst case day for a lot of reasons(usually fairly cold but not the coldest but very windy day is the worst case, infiltration makes a lot of heat loss).

By making the boiler a little bit smaller than the EDR of the system you can not completely fill the system with steam which will help a bit with short cycle times if the installed emitters are oversized.

Once the radiators are filled with steam they are the temp of steam and the output will be directly related to the EDR of the radiator. Once the boiler is big enough to produce enough steam to fill the entire system with steam the output of the emitters will be the same regardless of how much bigger than that the boiler is.

If the boiler is producing more steam than the system can consume it will produce pressure in the system. Water in the boiler under pressure has to be heated a bit hotter to boil so it reduces the amount of heat that transfers from the burner to the system a bit.

Eventually this pressure will build to a point where a vaporstat or pressuretrol shuts off the burner. The boiler will continue to steam from the residual heat until the system consumes enough steam that the pressure drops and fires the burner again. The ideal is that you don't produce more steam than is needed and the boiler never cycles off on pressure. If the boiler is significantly oversized this will happen every couple minutes until the thermostat is satisfied. If the boiler matches the system it will rarely if ever shut down on pressure.

How long it takes to satisfy the thermostat depends on how the radiators were sized 100 years ago, the current outdoor conditions, and what temp you want it at indoors. The longer that time is the more ven and comfortable the heat will be.

Note that every time the boiler cools down and has to heat back up to steaming there is heat lost to the basement and up the flue. Fewer cycles with a boiler firing at a lower rate use less fuel.

mattmia2

@hot_rod is there and idronics that covers building heat loss/gain? I din't see one unless it is in the one on heat transfer.

PiperPete

TO: mattmia2

Thanks for your very detailed explanation. It goes a long way to clarify what determines how long it takes to reach the set temperature.

Though I'm an electronics engineer, I am a total novice when it comes to hydronics and steam boilers: Math formulas don't intimidate me, so if you can suggest any formal book(s) on boiler operation for a newbie (if such books even exist) which covers theory with basic formulas, etc, I would be very interested in reviewing that.

Thanks again!

random12345

@PiperPete I get your concern, but the boiler/steam piping and thermostat are two different systems. Your chosen boiler IIRC is the CGSC50 rated at 354, your EDR is 316.67. So it's 11.8% oversized. There may or may not be cycling on pressure, but I would guess not. If you had gone with the SteamMax, it would have been rated at 321, which is basically spot on. Once the boiler turns on, the near boiler piping should start to get too hot to touch within a few minutes, and at that point you know steam is being generated. After that it probably shouldn't take more than 3-4 minutes to reach the main vents at the end of your steam main assuming the vents are large enough and pipes are insulated but it could take a few minutes longer if either of those things is not true. Just touch the main vent and time how long it takes to get too hot to hold once the near boiler piping is hot. Don't burn yourself. After that, depending on whether or not your radiator venting is balanced, the rads should start to get hot a few minutes thereafter. If any of them don't get hot at all, that's a problem. If it takes 15 minutes for any radiator to start to get hot, I would say that is also a problem, and the venting on that radiator needs to be adjusted. Venting is explained here:

https://heatinghelp.com/assets/documents/Balancing-Steam-Systems-Using-a-Vent-Capacity-Chart-1.pdf

The time it takes to satisfy the thermostat is a completely different question that depends on building total and room heat loss and radiator size and where the thermostat is located. Impossible to put a number on this. As long as all your radiators are hot all the way across in the time I outlined above, the system is working.

mattmia2

"We Got Steam Heat" is the homeowner level book written by @DanHolohan and "The Lost Art of Steam Heating" is the trade/engineer level book on steam systems.

Idronnics by Caleffi is a great series of articles that is essentially a hydronic heating textbook in a series of articles. I would recommend the one on heat transfer to understand more about how heat loss of the building and heating by the radiators works:
https://idronics.caleffi.com/magazine/23-heat-transfer-hydronic-systems

PiperPete

To mattmia2:

Thanks for the book suggestions, I will look them up on Amazon.


To random12345:

Thank you for the information and procedure to go through.
Yes, the CGS50 boiler is rated at 354, and my EDR calc (which I previously posted) is 316.7. What I can now say with some certainty is that my risers are not insulated, and though I can't know for sure, I suspect they are not insulated in the walls or pathways up to the 1st and 2nd flrs, so there's likely heat loss there. The there's infiltration of cold air from the outside in the Winter months because with a building like mine there was no additional insulation; it's brick walls, with space, then wood-lathing covered with plaster. The air between the walls serves as some insulation, but no doubt cold air gets in many ways, so that represents for heat loss. So I don't know if that additional 11.8% the boiler puts out helps with the unknown heat loss.

I also read from U.S.Boiler that boiler numbers are conservative and the number indicated by all boiler makers is actually 33% higher than indicated - that's quite a large difference - and is referred to as a "make-up" factor, to account for piping loss. Here's the link to that article:

https://www.usboiler.net/sizing-steam-boiler.html

In any event, I will have to go through the procedure you mention and see what it yields and perhaps post it here for further review.

Thanks !

Jamie Hall

To try and answer how long... there is another factor which hasn't been mentioned (that I've seen): how long to reach the thermostat setpoint, starting at what initial temperature? If you are holding a constant temperature on the thermostat, most thermostats will let the temperature drop a half a degree or so before turning on. Then how long the system will run to get the thermostat to turn off (typically half a degree above the setpoint) depends on how big the radiators are in relation to the current heatloss of the structure. If it's really cold out, and the radiation is closely sized to the heat loss, it may take quite a while (in fact, in the extreme case of the radiation ouput being equal to the heat loss, it never will shut off). On the other hand if it's warm out, so that the radiation is much oversized with relation to the heat loss, the system may call for heat for only 10 or 15 minutes and rest for an hour or more.

Now if you add in the possibility of turning the thermostat down -- a setback -- and then back up, it may take quite some time (my own boiler, Cedric, takes about 45 minutes to recover from a 2 degree setback on a 30 degree day, for instance, but on the same day, holding a constant temperature, he will only run about 10 minutes every hour or so.

An analogy might help. Consider your house to be a nice big capacitor. On one side, feeding it, you have a current limited power supply *your boiler) which also has a target turn on and turn off voltage (the thermostat). On the load side you have a variable resistance (your heat loss). Now let us suppose that your load current is very much less than the supply current. When the capacitor volage drops enough, the power supply turns on and, since it is pumping much more current in that the load is drawing, the capacitor will charge quickly to the turn off voltage. Now if the load draw is close to the limit of the power supply, it will take very much longer to charge the capacitor to the turn off voltage -- and if the load is greater than the power supply, it will never get there (note that if it is a resistive load, the current draw drops with voltage, so the system will stabilise at some lower voltage). Now if the capacitor starts at a significantly lower voltage, clearly it will take longer to reach the turnoff voltage.

Over simplified, but that may help?

Jamie Hall

Edit: the constant current source in the analogy up there is the installed radiation, not the boiler.

mattmia2

we have been trying to explain to you for 3 pages here that there is a 33% pickup factor baked in to the edr that boiler manufactures put on their rating plate and even for your uninsulated piping that is probably significantly more than the loss from your piping

btw, idronics is free to download

PiperPete

To mattmia2, Jamie Hall, random2345:

I can be a hard student, but I have a steel-trap mind... So I've been told.

However, after all this hydronics stuff, that steel-trap mind will likely turn to cast-iron and crack.

Seriously, though, I do appreciate the patience everyone has shown, and the information and comments provided. It would be great to take some courses on hydronics and sizing, etc. but I guess that's not something that's taught very much these days. Just a thought.

I just ordered the "We Got Steam Heat" from Amazon... Glad to hear idronics is free to download, I will check out the website tomorrow.

I will like not post here again until after the new boiler goes in starting on Monday and runs for a couple of days.

So, thanks again all, and have a great weekend!

ChrisJ

The DOE rating of your boiler should be it's actual output.  The EDR rating has the 33% BS in it while the DOE does not.

Ignore the sqft EDR rating and look at that.
If you take the EDR of your radiators and multiply it by 240 it gives you the BTU/h rating of them.

PiperPete

ChrisJ said:

The DOE rating of your boiler should be it's actual output.  The EDR rating has the 33% BS in it while the DOE does not.

Ignore the sqft EDR rating and look at that.
If you take the EDR of your radiators and multiply it by 240 it gives you the BTU/h rating of them.

To Chrisj:

Thanks for that input chrisj. Based on what you've provided here's what I come up with:

Some definitions:
- EDR = Equivalence of Direct Radiation, 1 EDR = 240 BTU/hr.
- MBH = 1,000 BTU/Hr. = 1 MBH
- BTU = British Thermal Unit

Ok, on page 1 of this thread I originally calculated the total EDR of my all radiators (1st and 2nd floors) and posted that, but it was incorrect because I was using a Columnar Radiator table.
After posting an image of one of my radiators (they are all the same except for height and number of sections) it was identified as a Tubular Radiator, and I recalculated all radiator EDR using the table corresponding to Tubular Radiators and that new table is also posted on page1 here.

One of the comments back on page 1 said the total EDR looked correct, presuming I counted the correctly.

So, prior to a final count of total EDR I double-checked my radiators for number of sections/height and recalculated EDR.

Also, as I noted in the revised table, for some radiators there were no exactly corresponding height in the table, so I rounded it up to the next highest radiator; For example, if my radiator measured 22", because there is no 22" in the table used matching the number of sections, I used the next taller radiator (by 1 inch),or 23". This would of course push up the total EDR but better slightly higher than under sizing the total EDR.

So, this recalculation resulted in my total EDR of 316.71 which I rounded up to 317 EDR.

Using your number 240 multiplied by the EDR to get BTU we have:

1 - EDR x 240 = BTU .... 317 x 240 = 76,080 BTU

I'm presuming that the 240 x EDR yields BTU/hr.

So it's = 76,080 BTU/hr

Now, and please correct me if this is in error, I am going to say that since there is energy loss between the input BTU and output BTU, the 76,080 BTU is what is required on the OUTPUT side of the boiler going to the emitters (Radiators).

2 - Looking at the specs table for the New Yorker boilers shows for the model CSG50:



The INPUT (Gas) MBH = 138 which is 1000 X 138 = 138,000 BTU (this corresponds with the BTU indicated in my contractors proposal), however, this is the INPUT BTU.

3 - The OUTPUT BTU (from the above chart) shows two numbers,

113 MBH (DOE Heating Capacity),
85 MBH (NET AHRI Steam)

In terms of BTU, these two numbers equate to 113,000 BTU/hr, and 85,000 BTU/hr, respectively.

The 113,000 BTU/hr. correlates with the stated maximum efficiency of 82.2 % in the chart above:

Output BTU/hr. (DOE Heating Capacity) = Input BTU/hr x Efficiency =

138,000 BTU/hr. x 0.822 = 113,436 BTU/hr. (the chart drops the 436 BTU/hr. and shows 113 MBH)

4 - However, the efficiency (boiler) is different when using the Net AHRI Steam Output number:

Efficiency = 85 MBH (Net AHRI Steam) / 138 MBH (Input GAS) = 0.616 (to 3 places) or 62 % (rounded up).

Efficiency (Net AHRI Steam) = 62 %

5 - Efficiency2 (Net AHRI Steam):

138,000 BTU/hr (input) x 0.62 = 85,560 BTU/hr.


6 - So, based on the above there are two efficiencies and OUTPUT BTU/hr. ratings:

a) Output BTU/hr (DOE Heating Capacity) = 113,00 BTU/hr.

b) Output BTU/hr (Net AHRI Steam) = 85.560 BTU/hr.


7 - Looking at #1 above which shows the energy required in BTU/hr. based on the EDR and using either the DOE Heating Capacity or the Net AHRI Steam, we have:

76,080 BTU/Hr. (EDR conversion to BTU/hr.)

The 76,080 BTU/H. number is less than either the Output BTU/hr (DOE Heating Capacity) of 113,000 BTU/hr. and less than the Output BTU/hr. (Net AHRI Steam) of 85.560 BTU/hr.

8 - So it would seem that the CSG50 is not undersized??? YES... NO... ???

If anyone feels this is not the case please provide an explanation.

Thanks again chrisj !

KC_Jones

The difference in those outputs has zero to do with efficiency.

Subtract 33% of the output as a “piping and pickup factor” for steam systems.

What Chris is saying is you have a gross output of 113,000 btu and you need 76,000

So 113-76=37
37/76=.486 or 47.6% pickup factor or excess capacity.

That is enough to support 247 feet of 2” main piping.  Even if you needed up to the rating of that boiler, 85k you would have enough pickup factor to support 187 feet of 2” piping.

What Chris is getting at is there are those of us that believe the manufacturers rating end up with an oversized boiler, in some cases grossly oversized.

If you were to step down to the next smaller boiler you’d have a 10% pickup which coincidentally is what Chris is running on his system with zero issues.  In fact I’d argue he may have one of the best running one pipe systems around.

10% in your case is enough for ~53 feet of 2” main piping.  And to be doubly clear, that’s uninsulated main piping.  If it’s insulated that number probably grows by a factor of 10 or more.

PiperPete

To: KC_Jones

When you say....

"That is enough to support 247 feet of 2” main piping. Even if you needed up to the rating of that boiler, 85k you would have enough pickup factor to support 187 feet of 2” piping."

I have no knowledge of how the 2" piping runs from the basement and up within the structure: The building is 25 feet wide x 75 feet in length x 2 stories high, with a basement. So presuming there are two 70 foot runs of 2" pipe, one for each floor, that's 140 feet, and presuming another 35 feet riser feed from basement to 2nd floor, that's a total of 175 feet - these number are all a guess.

So, this gets back to the question is the boiler undersized or not, which based on the the 113 MBU raw capacity (or the Net AHRI Steam) is more than enough to meet the 76,000 MBU.

So is that a YES or a NO for the CSG50 KC_Jones ?

KC_Jones

The 2” piping in a residential application is typically only what you see in the basement, basically you will be able to see it all, if the basement isn’t finished.  Everything running between floors is runouts for radiators and not mains.

The boiler you are getting is far from under sized and with the numbers I ran I even feel it’s more oversized than anything.  That said no contractor will size it down from what you are getting, well a couple might, but they are rare.

pecmsg

KC_Jones said:

The boiler you are getting is far from under sized and with the numbers I ran I even feel it’s more oversized than anything.  That said no contractor will size it down from what you are getting, well a couple might, but they are rare.

Doing it right is becoming rare. 

PiperPete

Th

KC_Jones said:

The 2” piping in a residential application is typically only what you see in the basement, basically you will be able to see it all, if the basement isn’t finished.  Everything running between floors is runouts for radiators and not mains.

The boiler you are getting is far from under sized and with the numbers I ran I even feel it’s more oversized than anything.  That said no contractor will size it down from what you are getting, well a couple might, but they are rare.

That makes me feel a bit better about the particular model.

I have no experience with boiler changeouts (this is not something one does on a regular basis, thank God) at least not for residential use. So I have no idea how the new boiler will perform, and more importantly how it will compare to the Weil-McClain with its 160,000 BTU raw output (it's 200,000 BTU/input). I'll know sometime Tuesday when the new boiler is fired up. It's going to be interesting.

Thanks KC_Jones

TonKa

PiperPete said:

b) is there an industry metric on what is considered to be a "reasonable" amount of time to meet the thermostat.. Thanks!

No, there is no standard I've ever come across. It seems like the industry answer, depending on who you talk to and what stage the project is in, is: somewhere between "long enough that the boiler doesn't kill itself by short cycling" and "as long as you're not cold, it should be forever".

It takes increasing levels of complexity to march toward the theoretical ideal of "forever". However, you can get far in the real world without ending up in a ditch with just a cheap thermostat and the expert opinions here. 🙂

PiperPete

TonKa said:

PiperPete said:

b) is there an industry metric on what is considered to be a "reasonable" amount of time to meet the thermostat..

Thanks!

No, there is no standard I've ever come across. It seems like the industry answer, depending on who you talk to and what stage the project is in, is: somewhere between "long enough that the boiler doesn't kill itself by short cycling" and "as long as you're not cold, it should be forever".

It takes increasing levels of complexity to march toward the theoretical ideal of "forever". However, you can get far in the real world without ending up in a ditch with just a cheap thermostat and the expert opinions here. 🙂

I'm quite surprised there's no general standard that addresses time-to-comfort level (which I guess can be different from reaching the thermostat temp) but I guess that's the way it is.

Thanks TonKa...