[jsbeckton]

So a few years ago we bought an old house and the inspector said that we should replace our forced hot water heat boiler because it was very old, old enough that he didn't see a date anywhere. Now while this is probably good advice I would feel better about replacing the unit (it gives us no maintanance problems) if I could calculate how much we would save per year by replacng it. In order to do that I need to know the efficiency, so I looked at the information plate on the unit (Weil-Mclain) and it said:

Input (BTU) 210,000
Output (BTU) 168,000

So I figure that I can calculate the efficienfy, 168/210=0.8 or 80%. Which is much better than I had expected so I thought I must be missing something.

That being said I found this page advertizing new boilers (I know this particular one is too small to use for my replacement):

http://www.homeperfect.com/weil-mcl...353030373032&gclid=CJbkh9OW77MCFcU-Mgod5DYA1Q

On this page they also show the BTU input and output as 105,000 and 80,000 respectivley, which I would think means 80/105=.76=76% but the page lists the efficiency as 95.3%?

What am I missing?

 

[techpappy]

Ya got me. Doesn't make sense..output should be much higher..unless theyt are stating minimums at worst case scenarios..system design wise...I would call the manufacturer rep directly to discuss...hopefully someone else will be able to explain

 

[danpik]

I believe that rating is for 100% fire rate. These are what are refered to as Modulating fire boilers. Once the boiler is up and running at temp the flame modulates back to as low as 20% fire. This is where the efficency comes from. I installed one of these at my father-in-laws house a couple years back. 2800 Sf house, ultra 80 boiler. Took the house from 1 zone to 3 zones and added a 50 gal "boilermate" water heater. Western NY winters and never had a cold day in the house. Also lowered his heating bill by almost 40%. Most of this was due to the way we zoned this house.

If you have one installed, make sure the installer knows how to do the install properly. These are not plumbed the same way as a conventional boiler. They need to have the "Boiler Loop" installed to prevent cold shocking the heat exchanger. This install requires a min of two circ pumps.

Pretty cool to watch the flame modulation guage as the unit is running.

 

[yuri]

So a few years ago we bought an old house and the inspector said that we should replace our forced hot water heat boiler because it was very old, old enough that he didn't see a date anywhere. Now while this is probably good advice I would feel better about replacing the unit (it gives us no maintanance problems) if I could calculate how much we would save per year by replacng it. In order to do that I need to know the efficiency, so I looked at the information plate on the unit (Weil-Mclain) and it said:

Input (BTU) 210,000
Output (BTU) 168,000

So I figure that I can calculate the efficienfy, 168/210=0.8 or 80%. Which is much better than I had expected so I thought I must be missing something.

That being said I found this page advertizing new boilers (I know this particular one is too small to use for my replacement):

http://www.homeperfect.com/weil-mcl...353030373032&gclid=CJbkh9OW77MCFcU-Mgod5DYA1Q

On this page they also show the BTU input and output as 105,000 and 80,000 respectivley, which I would think means 80/105=.76=76% but the page lists the efficiency as 95.3%?

What am I missing?

You are calculating/looking at Combustion efficiency which is the amount of heat you get from burning 1 cu.ft natural gas. That is not the same as "operating efficiency" AFUE google AFUE for more info. A sealed combustion boiler costs less to run as it takes no air from the house to feed the fire which is what your old one does. We use AFUE which is like the EnerGuide ratings/stickers on appliances to tell you how much it costs to run per day so you can compare the actual operating costs.

 

[danpik]

Smacks palm to forhead. Dooooh, sometimes the ole grey matter needs reminding.

 

[jsbeckton]

Ok, so what I am gathering is that these numbers can't be used to determine efficiency, I need to google the model and try to find the AFUE rating which I can then use to compare operating costs to a newer model. Right?

I just replaced the hot water heater a few months ago, too bad i didn't know I could have added a "boilermate" heater!

 

[danpik]

You can add one to any biler system. Most older boilers are so oversized that they will work fine...just need to add an additional zone. These newer ones have a domestic hot water priority feature that allows the boilermate to get the hot water over the other zones so the recovery is awesome.

You can always sell the current heater you have or hook it up as a backup. The nice thing about the boilermate heaters is they have no fire burning under them. I know of one in my buddies house that is going on 25 years old and never had a problem

 

[beenthere]

Unless your current boiler is a steam boiler, good chance its over sized for your home. A proper sized boiler will save you more money they just getting a new boiler of the same size.

The Weil McLain Ultra gas boiler is a mod con boiler, and an save you 30% or more on your heating bill.

 

[jsbeckton]

Ok, so I tried to look the model up and didn't come up with anything (Weil-McLain P-E-&, Series 3). Anybody have any info on this model? Guess this is a sign of how old it is. FYI, our house is about 2800 sqft not counting a full basement. How oversized is it?

Think I saw one site that said 75BTU/sqft which would put it at 210,000BTU which is what this one is. How oversized is that?

 

[jsbeckton]

Sorry, Model "P-E-7" not P-E-&

 

[NiNe O]

heat calcualtion required to determine the "exact" size for your home, anything short of that and it is a guess.

 

[beenthere]

Ok, so I tried to look the model up and didn't come up with anything (Weil-McLain P-E-&, Series 3). Anybody have any info on this model? Guess this is a sign of how old it is. FYI, our house is about 2800 sqft not counting a full basement. How oversized is it?

Think I saw one site that said 75BTU/sqft which would put it at 210,000BTU which is what this one is. How oversized is that?

Probably around 80,000BTUs, of course thats just a guess from my chair.

 

[danpik]

Think I saw one site that said 75BTU/sqft which would put it at 210,000BTU which is what this one is. How oversized is that?

Any good installer/salesman will do a proper heat load calculation on your house before they sell/install anything.

I do what we call "overbook" installs for a local company. If there is a large call for installs at my friends co. they call me to help out. I do about 15-20 installs durring the heating season. Mostly boiler replacements. I don't think in the 25+ years I have been doing this that I ever changed a heating plant "BTU for BTU" In my father-in-laws house, I went from a 175,000 BTU unit down to a 80,000 BTU unit. Granted, it went from a 80% to a 93+% which helped but the heat load calc came in right near 80,000. Probably the worst case I ever saw was a 250,000 BTU forced air unit in a well insulated 1500 SF house. I did not work the job, but from what I remember they also had something like 4 times the tons of cooling that was needed. The previous owner was one of those..."some is good, more is better, biggest is best" kind of people.

Ok, so I tried to look the model up and didn't come up with anything (Weil-McLain P-E-&, Series 3). Anybody have any info on this model? Guess this is a sign of how old it is.

If you can post a picture of it one of us here might be able to tell roughly the age. Might not be as old as you think. Aside from the lower efficiency, age is not a good reason to just change out a boiler. I changed out my 1959 boiler a few years back,not because it was old, but I needed to move it from the center of my basement and into a utility room I was building in the corner. this was done primarily because I needed to remove the chimney from the center of my house.

 

[jsbeckton]

Ok, contacted the manufactuer and they said that model was made between 1970-75 but that the don't have an efficiency information on units of that age. Can anybody venture a guess as to what it might be or give me a bounding value, say that it can't be more than 65% or something like that?

 

[NiNe O]

Someone not setting the gas pressure correctly would cause a swing of 10% or more in lost efficiency. You would need a team of engineers to figure that one out.

 

[jsbeckton]

I happen to have a Masters Degree in Mechanical Engineering so maybe its time ot break out the old Thermodynamic books!

Was hoping that some "seasoned" contractors would be able to save me some work (lazy).

So would the gas meter be a good enough gage (assuming nothing else is drawing gas) to determine my energy input (Qin) and the change in boiler water temp (before the pump turns on) be my delta Temperature? Guess I would need to know the volume of the boiler to determine the mass of water:

Heat Rate:

Qout=mCpDetaT
Qout=mass x heat coefficient x Change in Temperature

Thermal Efficiency:

n=Qout/Qin

Again, I would have to double check my equations but does this seem reasonable? Also, the boiler is stamped "Water = 146.1". Does this sound reasonable for the volume of water in the boiler or would this be the volume of the whole system or the max volume of the system?

 

[NiNe O]

Btu in from meter, ok.
Volume ummmm, shut off boiler and drain it? Fill it, heat it do your math.

 

[beenthere]

Ok, contacted the manufactuer and they said that model was made between 1970-75 but that the don't have an efficiency information on units of that age. Can anybody venture a guess as to what it might be or give me a bounding value, say that it can't be more than 65% or something like that?

80% Steady State Efficiency. 60 to 65% maybe 70%(with flue damper) Annual Fuel Utilization Efficiency.

 

[techpappy]

A boiler that old is likely giving combustion eff of 80% MAX then there is the AFUE as previously stated in a round about way..I would estimate ..best case scenario, providing the heat exchanger is squeaky clean..best overall efficiency at 60%..and as low as 50%...also depends on operating temp and flue gas temp..1/8 inch internal scaling or fireside sooting will cause noticeable increase in stack temp and loss of efficiency..I once tested an oil fired domestic boiler at 1000 deg F stack temp..finally talked the owner into going standard low eff gas and saved 60%. So, lots to consider..IMO you would save at least 40% by replacing with Hi Eff, condensing boiler..Note: run max 140 F ..and utilize indoor/outdoor control..most old radiators will provide adequate heat at peak temp of 140 F or less. Lower you can get away with the better. I would change it.

 

[jsbeckton]

Wow, if I am at mid 50's and paid about $2200 in gas last year (a relatively warm year with decent NG prices at that) I could save up to $800/yr by upgrading to a HE boiler at above 90% according to the DOE website. Maybe a bit more if my current boiler is oversized I guess. One other thing that I read was that I would have to have my old unlined flue lined to use a HE boiler due to more acidic gas.

So, I know I would need to get a few HVAC contractors out here for good estimates but any idea the range of cost I would be looking at to replace the current unit with a HE unit (90-95%) and have a liner installed in the flue? The boiler is in the basement of a 2 story house so it would be essentially 3 stories of lining.