Gas Bills Don't Lie

Cliff Brady

Gas Bills Don't Lie

Gas how water heat 75 foot long single 3 inch main pipe loop with top and side gravity takeoffs to 11 radiators in 2 story 4 bedroom house.

Gas hot water heater, stove, and clothes dryer also used.

Slant-Fin heat calc said 100,000 to 110,000 BTU/Hr. After the fact, I took a closer look at the gas bills and made the table below. All meter readings are actuals not
estimates.

A text Table of the analysis is attached below.

Definitions:

Design Temp of -10 degrees therefore 75 degree days in a design day is used below.

Input BTU/HR at -10 = (((Therms/Degree Day)/75 degrees)/24 hours) * 101,000 BTUs/Therm

Adjusted Therms/Degree is an attempt to include only degree days that are below the WWSD (warm weather shut down) which in this example I use 60 degrees
so 65 - 60 = 5 degrees removed per day so
Adjusted Therms/Degree day = Therms/(Degree Days - (5 * # of days))



The old boiler looks about double the needed size but it is typical or on the small side for most of the similar circa 1905 homes around here.

Do you see any flaws in this analysis? Would you do the analysis any differently? Assuming no radical changes planned for the house does it really tell you what size boiler (condensing of course ;) ) the replacement should be?

I will post the boilers proposed by contractors and the actual job after some discussion from The wall. No prices of course.

This thread has some overtones to the thread posted today on "Seizing a Munchkin" sp.

I appreciate any input you may have as this could be a good way for home owners and contractors to at least get a reasonably sized boiler.

scrook_2

Therms...

A Therm is 100,000 BTU not 101,000 BTU (a small difference, but) Natural gas (primarily methane) is about 101,000 BTU/ hundred cubic feet, though it varies slightly from month to month as propane/nitrogen is blended in to meet peak demand w/o significantly changing the heating value), hence the practice of conversion of meter reading in CCF to Therms at the prevailing BTU content that month.

LEAD PIPE

Nice

I just got my bill today, 45% less gas used over last Dec. I am so happy with this Ultra.

Cliff Brady

So, how do the therms per degree day compare?

This will eliminate the vagaries of gas pricing and demand to see what the actual increase in efficiency is. W

Cliff Brady

You are right. The gas bill takes the BTUs per cubic

foot of gas into therms for me. Not much in terms of actual error.

Cliff Brady

Heat loss! Heat Loss! Heat Loss!

We hear that all the time around here, but what about current Heat Usage when replacing boilers in existing structures. Come on Pros, I would like to hear from you. Do you try to get a look at the gas bills to find the maximum size boiler needed, or is always room by room heat loss calcs? I know you guys aren't using the three finger method.

Do therms per degree day extrapolate well as temperatures approach design or do they get geometric?

Which do you trust more heat loss calcs or therm usage?

I have interest in this as I have friends looking to replace their boilers for various reasons so I would like to be confident in recommending to them that they figure out thier BTU per degree day usage before they accept any bids for oversized boilers.

LEAD PIPE

Cliff

I don't know about those calculations. you speak of, but I see on my bill that the Jan 04 reading 217.000 CCF vs 383.000 CCF on the Jan 03 reading. This is the first month that it was under 50% savings. This boiler was expensive and everyone told me I was nuts, my boiler was 30 years old but running fine. The Ultra should pay for itself in 3 years then its all gravey. If this boiler only lasts 10 years I will be happy with it. Like I said I don't know about calculating this or that but I know how much cheaper my gas bill is I can tell you that.

Steve Ebels

Heat loss vs. therm usage

The one major thing that a good heatloss calc will do for you is pinpoint which areas are high or low. This enables an astute technician/designer to place the correct amount of BTU's in a given area. This can't be accomplished by looking at overall therm usage. That would only give you the big picture.

As far as looking at one or the other, I always try to get some good info on fuel consumption when sizing a replacement as well as doing a heatloss.

Mark Wolff

?????????

If you really are that concerned with an oversized boiler, and having the right btu output (presumably for fuel savings) I can't figure out why you are even considering Slant Fin. Their technology is almost as old as your house.

Look to Burnham, Weil-McLain Ultra or the Munchin boilers for higher efficiency. Wring every last btu out of your boiler instead of shooting out your chimney.

Unknown

Mark

I think Cliff said he used the Slant Fin heatloss software , he did not specify which boiler he would use - only that it be condensing .

And as far as Slant Fin's technology being old , some who post here would beg to differ ( although I must admit I do not know if they make a condensing boiler ) . Noel , Steve , are you around ?

Mark Eatherton1

Cliff,

Boiler Pro posted this response not too long ago. I think it's what you're looking for. A "real time" heat loss calculation backed up by real numbers.

The only precaution I'd give would be to make sure that you back out any electrical consumption at 3,413 btu/kwh from the net calculations and add that to the base hourly output requirements.

Here's what BP had to say...

Date: December 24, 2003 11:01 AM
Author: Boilerpro (boilerpros@ insightbb dot com)
Subject: Method of madness


Funny how the word madness is often used in the same breath as my name! Hmmm, wonder if that means something?

Anyway, our local natural gas supplier prints out much of the necessary data on the fuel bill. I start with the degree day data for the month being analyzed. Typically, this is the degree days with a base of 65F. In other words, the degree days don't start adding up until the average daily temperature is below 65F. For older single family, detached homes with a interior comfort temperature of 70F, heating is not needed until the temperature drops below 65F average daily temp. This is also termed the building balance point. Internal gains from people, lighting, sunlight, etc. generate enough heat to keep the building warm above 65F outdoors. You take the total degree days for the month and divide them by the number of days included on the bill. This gives you the average daily temperature delta tee for the structure, assuming a building balance point of 65F.

1200 degree days 65 / 30 day billing period = 40F

Around here, this represents a pretty typical mid winter month. The average outdoor daily temp for this month would be 65F - 40F = 25F.

As an aside, the design temp for us is -5F or 70F delta tee. If the daily temp is typically 25F and design is -5F your typical load is:

40F / 70F = 57% of you peak load. If you add an IBR pickup factor of 15% to you heating load, you are now at only 50% of the boilers peak design output. Hence, the long standing support of modulating or step fired heating plant. For 90% of the heating season you are need at most 50 to 60 % of your design day capacity. Back to the subject.

Next I take the therms used and divide them by the number of days in the billing period. Then this number, representing the average therms used per day, is divided by 24 and converted to btu's per hour input.

400 therms monthly usage / 30 days = 13.3 therms per day

13.3 therms per day/ 24 hours = .556 therms per hour or 55,600 btu/hr input

Now you have the average btu/hr input for the month (55, 600) and the average delta tee (40F). Dividing 55,600 by 40 will give you the number of btu's needed per 1F delta tee

55,600/ 40F = 1,390 btu/hr input/ degree F

This gives a good starting point to fine tune the heat load.

You have to watch out for out loads running through the meter, like water heating, etc. If you look at summer monthly bills, and building usage remains the same throughout the year, this should give you an idea how many therms per month go to these other uses.

Now, some experience and intuition comes into play. First off, is the balance point for the structure you are analyzing really have a balance point of 65F? Most newer structures do not. They often have balance points between 55 and 60. Lets say its 60F instead of 65F. For every day of the month you have to substract 5 degree days. So for the month in question:

1200DD65 -(5F x 30) = 1050 DD60 or 35F delta T

Something else that effects this is if the temperature in the structure is also set back for long periods of time. So lets say its one of the churches I work with and they set the temp at 50F and only warm it up on Sundays. The average temp of the space is only roughly 55F instead of 70F, so the delta tee just dropped by 15 F.

35F delta T - 15F = 20F delta T

So let's take the 60F balance point and low thermostat setting into account. We now get:

55,600 btu/hr / (40F -5F - 15F) = 2780 btu/hr/F input

Now for a couple of tough ones, what is the actual efficiency of the boiler during the month in question and what is the air leakage rate of the structure? Without getting a handle on these, it's pretty hard to get a good number for the actual heat load.

A great big firetube boiler idling a 180F all month, even when no heat is needed, is going to have a huge stand by loss. A newer compact cast iron boiler or even more so a copper tube boiler, only firng on demand is certainly going to be more efficient. I'd expext the firetube boiler would see an efficiency of probably 55% in this application so....

2780 btu/hr input/ F x 55% = 1529 btu/hr /F actual heat load

Then you also need to look at infiltration. This 1529 btu/hr is the combined load due to all types of loss. Typical conductive losses are basically linear through the temperature ranges we design for. However, infiltration accelerates nonlinearly as the temperature difference increases between indoors and out. This 764btu/hr/F needs to be corrected to reflect this. In very leaky structures this can be very significant and much less so for tighter structures. For typical structures, when the raw load is calculated at a delta tee of about 25 to 30, I usually add about 15% to compensate for the added heat loss of increased infiltration. In our case the delta tee is a little low so we need to correct a little more for infiltration. So.....

1529btu/hr x 1.20 = 1834btu/hr

This 1834 btu/hr would be the same as the peak UA calculated from a detailed heat loss.

While this all may sound complicated and iffy, with the kind of experience and understanding you have, it can be quite accurate. Also, going through this really helps give you a "feel" for the structure and, as stated prevously, is a great starting point for sizing baseload boilers. In my opinion, this baseload is where the payback is for the investment in expensive, high efficiency equipment. No sense spending money on high efficiency equipment that almost never runs.

Hope this gives you something to "chew on"

Boilerpro

Mark Wolff

Oops

I misread his statement. As for Slant/Fin I just think they are a second tier boiler. If you look at their design, construction, efficiency. Yeah they will get a person by, but I wouldn't really try to put them in the same league as a top of the line boiler gas or fuel oil. And if the guy is that into doing accurate heat loss calculations, I figured he would probably want a top shelf high efficiency boiler too.

Cliff Brady

Sorry this post digressed

slamming a manufacturer's products. I appreciate Slant Fin's free heatloss software and their participation here at The Wall. Even if other data indicate a different total heat load than the software, it does give a nice relative heat loss per room or floor, and it is easy to use!

Cliff Brady

> Boiler Pro posted this response not too long ago.

> I think it's what you're looking for. A "real

> time" heat loss calculation backed up by real

> numbers.

>

> The only precaution I'd give would

> be to make sure that you back out any electrical

> consumption at 3,413 btu/kwh from the net

> calculations and add that to the base hourly

> output requirements.

>

> Here's what BP had to

> say...

>

> Date: December 24, 2003 11:01 AM

> Author: Boilerpro (boilerpros@ insightbb dot com)

> Subject: Method of madness

>

> Funny how the

> word madness is often used in the same breath as

> my name! Hmmm, wonder if that means something?

> Anyway, our local natural gas supplier prints out

> much of the necessary data on the fuel bill. I

> start with the degree day data for the month

> being analyzed. Typically, this is the degree

> days with a base of 65F. In other words, the

> degree days don't start adding up until the

> average daily temperature is below 65F. For older

> single family, detached homes with a interior

> comfort temperature of 70F, heating is not needed

> until the temperature drops below 65F average

> daily temp. This is also termed the building

> balance point. Internal gains from people,

> lighting, sunlight, etc. generate enough heat to

> keep the building warm above 65F outdoors. You

> take the total degree days for the month and

> divide them by the number of days included on the

> bill. This gives you the average daily

> temperature delta tee for the structure, assuming

> a building balance point of 65F.

>

> 1200 degree

> days 65 / 30 day billing period = 40F

>

> Around

> here, this represents a pretty typical mid winter

> month. The average outdoor daily temp for this

> month would be 65F - 40F = 25F.

>

> As an aside,

> the design temp for us is -5F or 70F delta tee.

> If the daily temp is typically 25F and design is

> -5F your typical load is:

>

> 40F / 70F = 57% of

> you peak load. If you add an IBR pickup factor of

> 15% to you heating load, you are now at only 50%

> of the boilers peak design output. Hence, the

> long standing support of modulating or step fired

> heating plant. For 90% of the heating season you

> are need at most 50 to 60 % of your design day

> capacity. Back to the subject.

>

> Next I take

> the therms used and divide them by the number of

> days in the billing period. Then this number,

> representing the average therms used per day, is

> divided by 24 and converted to btu's per hour

> input.

>

> 400 therms monthly usage / 30 days =

> 13.3 therms per day

>

> 13.3 therms per day/ 24

> hours = .556 therms per hour or 55,600 btu/hr

> input

>

> Now you have the average btu/hr input

> for the month (55, 600) and the average delta tee

> (40F). Dividing 55,600 by 40 will give you the

> number of btu's needed per 1F delta tee

> 55,600/ 40F = 1,390 btu/hr input/ degree F

> This gives a good starting point to fine tune the

> heat load.

>

> You have to watch out for out

> loads running through the meter, like water

> heating, etc. If you look at summer monthly

> bills, and building usage remains the same

> throughout the year, this should give you an idea

> how many therms per month go to these other uses.

> Now, some experience and intuition comes into

> play. First off, is the balance point for the

> structure you are analyzing really have a balance

> point of 65F? Most newer structures do not. They

> often have balance points between 55 and 60. Lets

> say its 60F instead of 65F. For every day of the

> month you have to substract 5 degree days. So for

> the month in question:

>

> 1200DD65 -(5F x 30) =

> 1050 DD60 or 35F delta T

>

> Something else that

> effects this is if the temperature in the

> structure is also set back for long periods of

> time. So lets say its one of the churches I work

> with and they set the temp at 50F and only warm

> it up on Sundays. The average temp of the space

> is only roughly 55F instead of 70F, so the delta

> tee just dropped by 15 F.

>

> 35F delta T - 15F =

> 20F delta T

>

> So let's take the 60F balance

> point and low thermostat setting into account. We

> now get:

>

> 55,600 btu/hr / (40F -5F - 15F) =

> 2780 btu/hr/F input

>

> Now for a couple of tough

> ones, what is the actual efficiency of the boiler

> during the month in question and what is the air

> leakage rate of the structure? Without getting a

> handle on these, it's pretty hard to get a good

> number for the actual heat load.

>

> A great big

> firetube boiler idling a 180F all month, even

> when no heat is needed, is going to have a huge

> stand by loss. A newer compact cast iron boiler

> or even more so a copper tube boiler, only firng

> on demand is certainly going to be more

> efficient. I'd expext the firetube boiler would

> see an efficiency of probably 55% in this

> application so....

>

> 2780 btu/hr input/ F x 55%

> = 1529 btu/hr /F actual heat load

>

> Then you

> also need to look at infiltration. This 1529

> btu/hr is the combined load due to all types of

> loss. Typical conductive losses are basically

> linear through the temperature ranges we design

> for. However, infiltration accelerates

> nonlinearly as the temperature difference

> increases between indoors and out. This

> 764btu/hr/F needs to be corrected to reflect

> this. In very leaky structures this can be very

> significant and much less so for tighter

> structures. For typical structures, when the raw

> load is calculated at a delta tee of about 25 to

> 30, I usually add about 15% to compensate for the

> added heat loss of increased infiltration. In our

> case the delta tee is a little low so we need to

> correct a little more for infiltration. So.....

> 1529btu/hr x 1.20 = 1834btu/hr

>

> This 1834

> btu/hr would be the same as the peak UA

> calculated from a detailed heat loss.

>

> While

> this all may sound complicated and iffy, with the

> kind of experience and understanding you have, it

> can be quite accurate. Also, going through this

> really helps give you a "feel" for the structure

> and, as stated prevously, is a great starting

> point for sizing baseload boilers. In my opinion,

> this baseload is where the payback is for the

> investment in expensive, high efficiency

> equipment. No sense spending money on high

> efficiency equipment that almost never runs.

> Hope this gives you something to "chew on"

> Boilerpro

Cliff Brady

Thanks Mark

Boiler Pro and I were thinking right along the same lines. The only thing that is not clear near the end his post he concludes with 1834 BTU/Hr/F, but what number for F he would use to extrapotate BTU/Hr at design? It is little confusing since he has already factored out a lot Fs already.

Would you agree that if the replacement boiler is direct vent then the infiltration factor could be lower?

Mark, is 3,413 btu/kwh below to compensate for waste heat from electrical appliances that may or may not be running? I forgot how btus and kwhs convert, so is this a one to one conversion or a factored conversion?

;The only precaution I'd give would be to make sure that ;you back out any electrical consumption at 3,413 btu/kwh ;from the net calculations and add that to the base hourly ;output requirements.

The main reason for replacing the 30 year old Weil McLain 175,000 boiler and water heater was to remove the chimney to make room for kitchen renovation.

Anyway, after getting a very large bid for Burnham Revolution RV5 130,000 input with a 53 Gallon indirect and a very reasonable bid for a New Yorker powervent 175,000 input with an 80 gallon indirect, I instead went with a Peerless Pinnacle 140 with a 40 gallon indirect. neither bidder did a heatloss calc or asked to look at my gas bills.

At my max heatloss calc of 110,000 btus/hr the PI-140 looks reasonable at 112,000 btu output at high temps, but my after the fact analysis of gas bills makes Munchkin/Pinnacle 80 look very reasonable, and a little cheaper.

Mark/Guy/Bill is there any chance of a Vision One retrofit for pre-925 board Munchkins? I think someone else dropped this question in the middle of a thread here before but never got an answer.

Anyway, by one of my calculations we should stay warm down to -68 degrees!

Mark Eatherton1

Cliff 2

Infiltration, in my experience, is the ONE factor that we have little to no control over that can KILL us when it gets cold outside. Even though you're direct venting, it still needs to be taken into consideration. If the period of time you were analyzing were relatively calm as it pertains to wind, you might short yourself BTU's when it gets cold AND windy outside. If the period of analysis was relatively windy, you probably don't need to plug anything else into the equation.

As for electrical consumption, yes, you are correct. I'm assuming 100% conversion from electric to heat, and theres no guarantee that those same lights/appliances would be on during the next cold snap. Especially if you're gone to Florida on vacation...

The KWH compensation would also neeed to be broken down into an hourly chunk just to keep things relative.

As for converting a pre 925 board boiler to a V1, no, it unfortunatley can not be done. However, with the modulation capabilites of the technology you're dealing with it will still be light years ahead of the conventional ON/OFF technology that currently is being used. You could make seasonal adjustemnts to the set point. 180 degree F water is not REQUIRED to make DHW, its just what is used in the ratings. The Germans don't allow much more than 160 degrees F for the production of hot water, and they don't smell that bad:-) In fact, I met Dr. Lou V from Buderus yesterday, and he smelled just fine!!

Speaking of Buderus, they are going to be bringing a WHOLE bunch of great things to the market in the next year, including their wall hung condensing boilers. FINALLY!

Lastly, the 1834 buth/deg F is his bottom line input requirement. In other words, if it were 64 degress F outside, his home would be using approximatley 1,834 btu's per hour. SO you then have to adjust the total boiler size based on your gut feeling as it pertains to the balance point and your maximum reasonable design exposure.

So, if the home were here in Denver, and our design temperature is 5 above zero, then you would take the 1834 and mulltiply it times 60 (65 minus 5) and that would be the required input at 80% efficiency to guarantee comfort. If you're using an appliance with a higher efficiency, you can reduce the input in a direct relationship to appliance efficiency. In your case, you'd be safe in reducing the load by 10%.

Hope this didn't confuse you too much. I'm going to write an Excel spread sheet to do the numbers crunching for me, and will share it when I'm done.

ME

Cliff Brady

Modulating on DHW now

with DHW at 130 feeding the Dishwasher and Washing Machine with a mixing valve at around 115 for the rest of the house. I experimented with 160 degree setpoint 30 degree differential and settled on 170 degree setpoint. At least I think it at 170 since that is what the supply reads going to the dhw tank. It definately modulates on the way to 170. It may be at 160 degrees but modulates up to 170 as the temperature increases. That little setpoint dial is hard to read.

Given that fast recovery is not an issue I could crank it down another 10 or 15 degrees but there has to a reasonable differential between the 130 degree Hot Water temp and The DHW Boiler supply temp. So long as the indirect can absorb the 46,000 btu minimum output of the PI-140, I'm happy. It will still probably run at full flame 98 percent of the time in heating mode.

To bad about the V1. Maybe a 925 board retrofit? There must be some different boiler components and cables on the V1 models or otherwise I would think it would be a plug and play operation. The Munchkin 925 Board manual shows 'M and 'M HA' with different part numbers fo burners and wiring harness. One would guess the 'M HA' models were for high altitude but I haven't heard of a high altitude model.

Thanks again Mark.

Mark Eatherton1

Cliff 3

You would have to change out a WHOLE bunch of stuff in order to retrofit the 925. More than you really want to tackle. The HA is a high altitude model for use with LP gas. Has a different type of ignition system to deal with the difference in fuel density.

ME