examining my heating system, possible answer to why my boiler runs at 200F

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Old 12-28-11, 08:23 AM
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Exclamation examining my heating system, possible answer to why my boiler runs at 200F

I moved into a new (to us) house a year and a half ago. I’ve been going thru the house, making improvements, learning things and educating myself. I came across this site and for a few weeks now I’ve been reading about the boilers, heat loss calculation, tendency to have a boiler oversized and so on.

So I decided to spend some time and do some calculations. Here are the results if anyone interested (geeky people like me will be ):

My boiler: Repco LA100C circa 1980 running at 200F (historical reason, haven’t touched it yet). Input BTUs is 100k, heating capacity is 79k.
Baseboard: Slant Fin 15
2 zones for each floor in my 2 story house on insulated not heated basement.

Adequate insulation in the attic (17” of fiberglass everywhere, 26” maybe 50%) and basement (9”). Attic and unfinished part of the basement (50% of the basement) is air-sealed. Next year I want to pull the trim off the windows and make sure it’s all tight.

No sure about insulation in the walls, so worst case scenario – no insulation.

I did a heat loss calculation and it came out 58.7K BTUs for the house, 31.6 for the 1st floor and 27 for the 2nd floor. For 79K heating capacity of the boiler, it’s about 40% oversized.

I decided to calculate the heating output of all my heating elements to see how much heat can be transferred. My boiler runs hot (200F) so I did the calculation for water being 180F and 160F at the elements. It came out as:

180F at 4GPM – 56.9k BTUs (1st floor – 29.29, 2nd floor – 27.6)
160F at 4GPM – 41.2k BTUs (1st floor – 29.22, 2nd floor – 20.94)

So at 180F the output of the heating elements matches the heat loss of the house on the design day almost perfectly! It also seems that I would need to add more heating elements if I run my boiler colder or I would have to crank up the aquastat higher on the coldest day. So now I wonder if the system was undersized when it comes to the number of heating elements and thus the decision was made to run it hotter. I “foiled” 53” of the heating element on the second floor to balance the room temperatures, so before the output was 2.5K more on the second floor. Second floor baseboards are all closed in all the rooms except the one that is the coldest, so that’s skews the numbers for the output on the second floor a lot.

Bottom line for my exercise is that I need a boiler that outputs not more than 70K of BTUs per hour. It took me probably 2-3 hours to do this exercise, but I’m happy that I did it. If anyone sees something wrong in my logic, please let me know!

Thanks.
 
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Old 12-28-11, 09:06 AM
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Hello Diver,
How old is the house? I'm wonderng about insulation in the walls. My guess is it is in there. Possibly not.....

Trying not to sound to cynical, but maybe it's 200 degrees cause the oil guy set it there.

One thing i would comment is the loss for the second floor seems high, in my house the second floor and third floors need a very small fraction of the heat the first floor needs.

I'd lower the temoerature of that boiler yesterday, if i was you.
You can always turn it back up next month, if it ever gets cold this winter.

Talk to the boiler tune up guy about downsizing the nozzle one or two sizes.

Peter
 
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Old 12-28-11, 09:33 AM
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PeterNH,

The house was built in 1984. I used a worst case scenario for the wall insulation, it might just be full of insulation as far as I know.. It just seemed to me that the house loses a lot of heat fast, but I'm coming from a brick condo where it would stay warm forever...

you're right, it might be set at 200f due to the oil guy, i doubt anyone did any calculation. plus i did a lot of winterizing on the house, so it might not need the 200 anyway.

as for the high loss of the second floor - the floors are the same size and judging by the numbers in heat loss calculator, the heat loss should be very similar. 1st floor has floor factor of 0.02 (not heated, insulated basement) and 0 for ceiling. 2nd floor has it reversed, so it should be same. 2nd floor has less loss since there fewer windows/doors.

i could import the heat loss express 2 data and include here, if you would like to take a look. i'm new at this, so it's possible i missed something. one thing that seems strange in HLExpress is that changing indoor temperate didn't change the heat loss numbers.

Talk to the boiler tune up guy about downsizing the nozzle one or two sizes.
i thought i would be the boiler tune up guy this year are there any numbers for nozzle sizes? like one size is about 5% output or something like that?
 
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Old 12-28-11, 09:36 AM
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oh, yeah, design temp is 0F (Massachusetts)
 
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Old 12-28-11, 09:44 AM
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I'd lower the temoerature of that boiler yesterday, if i was you.
i plan on doing some major cleaning up of the airspace around the heating elements on the first floor this weekend and move the temp down the same time. hopefully these two compensate each other
 
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Old 12-28-11, 10:25 AM
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i thought i would be the boiler tune up guy this year are there any numbers for nozzle sizes? like one size is about 5% output or something like that?
Umm, i know this is the do it yoursef forum..
but you are literally playing with fire here.
Unless you have specialized tune up tools and know how to use them , imo that is a very, very, very, bad idea.

no offense,
Peter
 
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Old 12-28-11, 10:34 AM
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Peter,

Maybe I'm confusing tuneup and cleanup here. Are both not recommended to be performed by not so professional public?
 
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Old 12-28-11, 10:35 AM
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as for the high loss of the second floor - the floors are the same size and judging by the numbers in heat loss calculator, the heat loss should be very similar. 1st floor has floor factor of 0.02 (not heated, insulated basement) and 0 for ceiling. 2nd floor has it reversed, so it should be same. 2nd floor has less loss since there fewer windows/doors.

i could import the heat loss express 2 data and include here, if you would like to take a look. i'm new at this, so it's possible i missed something. one thing that seems strange in HLExpress is that changing indoor temperate didn't change the heat loss numbers.
If changing the indoor temp didn't do anything, then i'd say the program is useless.
Look around for another program to try.
I'm pretty sure there is a heat gain from the ceiling/first floor to the the second floor.
If you hang out down the cellar for an evening or so, like tonight when it gets real cold, you can time the on time for the first and second floor zones. Also time the on time for the burner.
If you have a good outdoor thermometer record the outside temps every hour.
Put all the data together and you can start to get an idea of actual usages, instead of theorectical.

Peter
 
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Old 12-28-11, 10:38 AM
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Maybe I'm confusing tuneup and cleanup here. Are both not recommended to be performed by not so professional public?
Certainly not until you have watched a good pro do it a few times.
I'll let NJT chime in on the soot cleaning health issues among others.

Peter
 
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Old 12-28-11, 10:49 AM
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PeterNH,

Slant/Fin Heat Loss Express is the one tool recommended here. It seems that it's stuck with 70F for indoor temp, that suits my needs, i will double check on some of the online calculators to make sure i'm in the bulk park.

But even if I'm not, the length of the heating elements puts me at slightly less than 60K BTUs/h. Since it seems to be sufficient for heating, I would stick with this number. If actual heat loss is smaller, then i would be a bit oversized if sizing the boiler to the heating elements.

Sounds like i should defer at least the cleaning/tuning to a professional. At least for the first time. This is a long shot, but maybe someone know a reputable company/contractor in the southern Mass?
 
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Old 12-28-11, 11:35 AM
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The house was built in 1984
I'll bet a lot of beers, there is insulation in the walls of a 1984 built house.

Maybe try and re-do the heatloss calcs.

Peter
 
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Old 12-28-11, 11:41 AM
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Sorry Diver,
Nothing down south.
Up here near the border maybe.

If you are in Southern Ma. are you sure the design is zero?
Check out this chart:
Multiple_boiler Installation


Peter
 
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Old 12-28-11, 11:54 AM
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you're actually close enough to my location to do "lot of beer"

i redid the number implying 2" of insulation in the walls. here is the summary:

no insulation:

1st floor: 31.6K
2nd floor: 27K
Total: 58.7K

2" insulation:

1st floor: 23.7K
2nd floor: 18.5K
Total: 42.2K

i was looking at different boilers lately to make sure i know what i want so i'm not hard-pressed to choose one in the middle of the winter in case my old boiler quits on me...

i did my research and i think i want a simple cast iron atmospheric non condensing boiler. my current one vents into a chimney (i believe there is dedicated pipe for it and my DHW heater) and i don't want to make another service opening for direct or closed combustion boiler. i don't have a drain available either. the price difference between sophisticated and a simple boiler might have ROI time in a decade or even more ..

so I was looking at burnham es2 series and i was thinking es2-4 (input/output 105k/77k). but now if my more realistic heat loss is under 50, should i consider es2-3 (70k/51k)?? kinda scary since my current one is 100k/79k..
 
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Old 12-28-11, 12:00 PM
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If you are in Southern Ma. are you sure the design is zero?
Check out this chart:
Multiple_boiler Installation
i looked at this site: Outdoor Temperature and Relative Humidity - US Winter and Summer Conditions

and it puts Boston at 0. you site says Boston is 9. I'm in Mansfield, the closest on your list is Fall river and it's also 9.

with design temp at 9 and 2" of wall insulation puts my heat loss at 36.7 total and floors at 20.6 and 16.1.

a little bit more convincing from your part and you will make me believe that i don't need a boiler at all

how can i determine if my boiler short cycles? what is the general rule of thumb? not doing hi to low temp cycles while pump is still running?
 
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Old 12-28-11, 12:07 PM
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Wait a minute Diver.

Some things do not compute...

First, redo the heat loss with 3.5 inches, but increase the inflitration.
I don't know where you could buy 2 inches of insulation in '84 unless they tried to split the 3.5 inch stuff in half. Not realistic.

Second...
Water heater/chimney???
Do you have natural gas??
If so why even think for a second about oil?
 
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Old 12-28-11, 12:26 PM
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3.5" insulation, not weather-stripping (infiltration factor) results in 34.7K. at 9F design temp

i have natural gas, the only time oil came up was when you mentioned the oil guy:

Trying not to sound to cynical, but maybe it's 200 degrees cause the oil guy set it there
 
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Old 12-28-11, 01:40 PM
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You don't want to try and down-fire a gas boiler... I think the talk about 'nozzles' might have caused some cornfuzzlement. Oil burners use nozzles, Gas burners use 'orifices'.

With a gas system there should be no issue with 'soot'... the only thing you should see is some rust... and of course wear a decent filter mask... if you do see black soot, there's a problem and that would need to be looked at. I see no reason why you couldn't clean a gas boiler as long as you know how it comes apart and back together. Just use common sense...

It seems that it's stuck with 70F for indoor temp,
I just pulled my HLEx program up and changing the indoor temp does change the heat loss... I think you need to change each room though... if you try changing it at "JOBS / EDIT " it doesn't work... seems that parameter is only for the initial entry of a new job.
 
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Old 12-28-11, 02:12 PM
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NJTrooper,

you're right about the confusion! so it seems that i should be able to clean the gas fired boiler that i have after all. i will worry about it come spring and probably will come back for some advise here!

and you're also right about indoor design temperature in hle2 program - changing on the job level doesn't do anything but it does on individual room level!
 
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Old 12-28-11, 04:08 PM
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I would expect a house built in 1984 to have insulation in the walls.

Here is a good exercise for you to do when the temps really dip near design. When the night time temp gets between 0 and 10 degrees, go out and read your gas meter and note the time and temp. In the morning, head back out to the gas meter and give it a second read and note the time and temp. You should do this by 7 am. You don't want to much sun on your house for this. Do some subtraction and figure out how much gas you used. Convert your cf used to BTU's. Multiply this by the efficiency of your boiler. Probably some where between 80%-85%. Divide that number by the number of hours that have passed. Average your temperature readings and that is your heat loss per hour at that average temp.

For boiler sizing, you want to use the DOE output. Heat loss software has a margin built into it. You wouldn't want to size your boiler exactly to what you figured out by reading your gas meter though. Having some margin is a good thing.
 
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Old 12-28-11, 05:20 PM
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Re: cleaning a gas-fired boiler. No cleaining should be necessary. My boiler, a fire-tube unit, hasn't been cleaned in over 50 years - unless you include brushing out the tubes every couple of years to remove minor rust particles that have fallen down to the invert of the tubes.

As far as replacing a functioning boiler solely for fuel savings, I have not seen a situation that justified that with a reasonable economic payback period. Boiler salesmen are almost all the same, even if they are genuine repairmen that get a modest kickback. They will under-estimate the efficiency of your existing boiler, and over-estimate the efficiency of the new boiler they want to sell you.

Do your own payback analysis - don't trust a boiler salesman to do it for you. Start off, just for grins, by assuming the the replacement boiler consumes zero fuel. If the new boiler costs, say, $10,000 installed, and you now spend $1,500 per year for heating fuel (which I doubt), then the payback would be 10,000 / 1,500 = 6.7 years. Now, run the calculation again with whatever annual fuel cost you or the salesman projects with the replacement boiler.

Personally, before replacing a boiler just for fuel savings, I would want to expect a projected payback period of five years or less - unless you knew you were going to live in the house for a much longer period.
 

Last edited by gilmorrie; 12-28-11 at 05:48 PM.
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Old 12-28-11, 05:20 PM
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If you can do this calculation on a crystal clear, windy night, all the better!

1 CF of natgas is about 1030 BTU
 
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Old 12-29-11, 07:29 AM
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guys, thank you for your responses, i really appreciate it.

drooplug,

Here is a good exercise for you to do when the temps really dip near design
i will try to do it, but it might be awhile before we get to that point. i recorded some numbers for last few days and it seems that i consumed about 15k BTUs per hour for 24 hour period. the temps were ranging from around 20 to about 50 during day.

For boiler sizing, you want to use the DOE output. Heat loss software has a margin built into it. You wouldn't want to size your boiler exactly to what you figured out by reading your gas meter though. Having some margin is a good thing.
well, to be honest with you i decided to simply size to the size of my heating elements in my baseboards. at 180F degrees circulating thru the system my baseboards cannot possibly output more than 57K BTUs. at 160F it's about 42K BTUs. so 60K heating capacity boiler would be ideal. the Burnham ES2 boilers that I was looking at lately has one with heating capacity of 51k and another with 77K. i think 51 is a tad small. my current one is 79K heating capacity.

gilmorrie,

Re: cleaning a gas-fired boiler. No cleaining should be necessary. My boiler, a fire-tube unit, hasn't been cleaned in over 50 years - unless you include brushing out the tubes every couple of years to remove minor rust particles that have fallen down to the invert of the tubes.
the manual called for that kind of cleaning - remove the flute cover and brush the exchanger. i planned on doing that, but was concerned that the rust would fall on the orifices. so i was thinking removing them before brushing. should i not?

As far as replacing a functioning boiler solely for fuel savings, I have not seen a situation that justified that with a reasonable economic payback period.
i am NOT replacing my boiler. I'm educating myself on this subject and researching possible options if i'm faced with a situation when i need to replace it quick. i don't want to be caught off-guard. my intention is to get another 20 years out of my current boiler. i agree with you completely on your calculations. my gas bill in the winter ranges from $100 to $200. if i boost the efficiency from 79% that i have to 85% (atmospheric boiler), i would save $145 per heating season. if it costs me $6k to get a new boiler, then it would take me 40 years to break even!
 
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Old 12-29-11, 08:17 AM
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For boiler sizing, you want to use the DOE output. Heat loss software has a margin built into it. You wouldn't want to size your boiler exactly to what you figured out by reading your gas meter though. Having some margin is a good thing.
well, to be honest with you i decided to simply size to the size of my heating elements in my baseboards. at 180F degrees circulating thru the system my baseboards cannot possibly output more than 57K BTUs. at 160F it's about 42K BTUs. so 60K heating capacity boiler would be ideal. the Burnham ES2 boilers that I was looking at lately has one with heating capacity of 51k and another with 77K. i think 51 is a tad small. my current one is 79K heating capacity.

Hello Diver,
The DOE output of the ES2-3 is 59,000
Probably way more than you need, but it does match up well with your installed radiation.


sorry about the confusion over Oil vs Gas earlier.


Peter
 
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Old 12-29-11, 09:04 AM
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concerned that the rust would fall on the orifices. so i was thinking removing them before brushing. should i not?
I would remove the burner tubes if it's an easy enough matter to do so... some just lift up and out. You want to clean the burner tubes also, get the dust out from inside them. If they don't come out easily enough, then cover them with sheeting, but vacuum them off as well as you can after the fact.

The actual metered gas orifice is located on the manifold to which the burner tubes are inserted. While the holes on the burner tubes are 'orifices', they aren't THE orifices...
 
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Old 12-29-11, 09:28 AM
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PeterNH,

you're right! i was looking at I=B=R rating. so it looks like ES2-3 might just be right for me

funny thing is ES2-3 which is smaller than ES2-4 actually costs more. but it should save more on gas, and payback should be short
 
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Old 12-29-11, 09:33 AM
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NJTrooper,

I was worried that i would have to disconnect the gas pipe for that. if that's not the case, i will try to get them out. otherwise i will cover them up before cleaning!

thank you all for all your help!!
 
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Old 12-29-11, 10:54 AM
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i will try to do it, but it might be awhile before we get to that point. i recorded some numbers for last few days and it seems that i consumed about 15k BTUs per hour for 24 hour period. the temps were ranging from around 20 to about 50 during day.
i forgot to adjust for my boiler efficiency. so it's about 11.8k BTUs used for heating and 15K consumed.

however, the gas was used for cooking and DHW, so the actual number are even lower. i will try to get some overnight numbers ...
 
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Old 12-29-11, 03:18 PM
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i will try to do it, but it might be awhile before we get to that point. i recorded some numbers for last few days and it seems that i consumed about 15k BTUs per hour for 24 hour period. the temps were ranging from around 20 to about 50 during day.
You should do it at night. During the day introduces too many variables. You will have hot water usage and cooking gas to contend with. You also have the sun introducing solar gain. This will throw off the numbers.
 
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Old 12-29-11, 05:57 PM
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yeah, but at night i have a setback
 
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Old 12-31-11, 03:02 PM
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when a boiler gets replaced, what other parts usually get replaced the same time?

the circulating pump is part of the boiler, so it would get replaced. how about expansion tank? pressure regulator? if they are in good shape, i'd assume they could stay, but maybe it's common rule to have at least some of them replaced when boiler is replaced?
 
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