Modcon vs CI Gas Usage - Baseboard Heat

David_16

I'm trying to keep it simple in this post.

I have options to install a 95% modcon and 84% CI at about the same cost. HW will be via indirect.

I have baseboard hot water heat with 2 zones (one zone fairly lightly used) and live on Long Island, NY. Design day temp is 15.

I understand that it's not an exact science, but assuming both units are properly sized, installed and programmed, what percentage gas savings would I expect to realize with the modcon? I know it won't condense a good portion of the time with baseboard, but I know the modulation factor should also make a difference.

I understand that I also have to factor in that the CI will likely last longer and cost less to maintain over time.

Jamie Hall

Well...your numbers are right there. The absolute maximum you could save would be the 11 % or so. That will assume that the mod/con is condensing all the time (which it won't be) and that both boilers are otherwise set up and operated optimally.

The modulation does make a difference -- but mostly so that the boiler can condense more of the time. Again, assuming that the mod/con is making use of all its features (particularly outdoor reset) and you don't do strange things with the thermostats. It will help some in reaching towards that 11 % -- but you won't get over that.

Hot_water_fan

I would add modulation helps unless the CI is also doing a good job thermally purging. A lot of new ones can do it, but it’s crucial to make sure leftover heat doesn’t remain in the boiler. Baseboard really isn’t a big deal in terms of return temperature. You’ll condense a ton. 

JMWHVAC

There is more to it than combustion test efficiency. Years ago we replaced an 81% efficient oil boiler with an 87% oil boiler. Also, old boiler had the old HW coil in it and new setup had an indirect water heater. The owner was very happy when he experienced 40% savings.

LRCCBJ

JMWHVAC said:

There is more to it than combustion test efficiency. Years ago we replaced an 81% efficient oil boiler with an 87% oil boiler. Also, old boiler had the old HW coil in it and new setup had an indirect water heater. The owner was very happy when he experienced 40% savings.

This is correct.

NONE of the combustion numbers relate to system efficiency. CI boilers will run much lower system efficiency due to the fact that you pay for that nice warm basement and almost all the energy goes right out through the foundation walls (above the grade) which, when typically uninsulated, have an R value of less than 1! It's similar to a large hole in your basement, 12" in height, and 80 feet in length (all around the basement).

Despite what claims are made, none of this energy is retained in the building unless, magically, the basement is warmer than the first floor (hot goes to cold).

I converted one house from a large CI boiler to a 75g Smith HWH. The combustion of the CI boiler was 78%. The combustion of the Smith HWH is estimated to be 69% (based upon their literature). The CI boiler routinely used 800 gallons of oil per year (112M BTU). The HWH (including some cooking gas) used 900 therms of gas per year (90M BTU). Clearly the "inefficient" HWH won this game.

There are some clear benefits to use a 75g well insulated HWH for both CH and DHW despite the lower combustion efficiency. The installed cost is roughly 50% of the cost of a modcon with indirect. Of course, this depends on the capability of the radiation to provide sufficient energy with the SWT at 140F.

David_16

Hot_water_fan said:

Baseboard really isn’t a big deal in terms of return temperature. You’ll condense a ton. 

Would you say that condensing 70% for baseboard on Long Island, NY is a conservative estimate?

Jamie Hall said:

Well...your numbers are right there. The absolute maximum you could save would be the 11 % or so. That will assume that the mod/con is condensing all the time (which it won't be) and that both boilers are otherwise set up and operated optimally.

The modulation does make a difference -- but mostly so that the boiler can condense more of the time. Again, assuming that the mod/con is making use of all its features (particularly outdoor reset) and you don't do strange things with the thermostats. It will help some in reaching towards that 11 % -- but you won't get over that.

This is helpful. I was under the impression that the modulation factor helps realize additional savings.

Are you saying that the absolute most the modcon could save me vs the CI would be 11% in gas costs (assuming everything is configured ideally)? If the modcon is condensing say only 70% of the time, then closer to 8%?

If I'm only going to save $150/year by going to the modcon, is that really even worth it considering that it may not last as long and probably will require more maintenance over time that will likely eat up that $150/year gas savings.

With the installed price being almost identical, this is what I'm struggling with here in my decision.

Hot_water_fan

Would you say that condensing 70% for baseboard on Long Island, NY is a conservative estimate?

Sounds about right. Widening the delta T would increase the % without any baseboard alterations. If the baseboard is already oversized (IE if heat loss can be met with under 180F AWT) then the % would be higher, if undersized, lower.

GroundUp

Jamie is sorely mistaken in his assertion. Combustion efficiency is only a small piece of the pie- the real savings come from modulation and lack of cycling. I've got quite a few systems that have reduced fuel usage by upward of 30% by doing nothing at all besides swapping a CI boiler for a mod/con with outdoor reset. Say it's a 70,000 BTU load at design temp, we can utilize an 80k mod/con that turns down to 8k and can run constantly on a 50 degree day rather than a 100k CI that fires for 2 minutes at a time when the load is only 8k/hr. Of course the actual numbers will be specific to your particular scenario and radiation, but there's almost zero chance that it's only 11% (or whatever the combustion efficiency spread may be). Something that does need to be considered is the lifespan and maintenance requirements of a mod/con which may end up costing more in the long run despite the fuel savings, so keep that in mind as well.

David_16

GroundUp said:

Jamie is sorely mistaken in his assertion. Combustion efficiency is only a small piece of the pie- the real savings come from modulation and lack of cycling. I've got quite a few systems that have reduced fuel usage by upward of 30% by doing nothing at all besides swapping a CI boiler for a mod/con with outdoor reset. Say it's a 70,000 BTU load at design temp, we can utilize an 80k mod/con that turns down to 8k and can run constantly on a 50 degree day rather than a 100k CI that fires for 2 minutes at a time when the load is only 8k/hr. Of course the actual numbers will be specific to your particular scenario and radiation, but there's almost zero chance that it's only 11% (or whatever the combustion efficiency spread may be). Something that does need to be considered is the lifespan and maintenance requirements of a mod/con which may end up costing more in the long run despite the fuel savings, so keep that in mind as well.

So much different information here. I had previously assumed what you said above was correct as it seems based on much anecdotal evidence that clearly a 95% modcon could save more than 11% in fuel costs over an 84% CI.

Your last sentence is where I'm at and why I started this. If I'm only going to save 8%/$150 (difference in AFUE and because it's not always condensing), I think I would go the CI route due to the lower cost of maintenance. If I could save 20%/$400, I'd probably go the modcon route as that difference probably more than offsets the higher cost of maintenance.

This is what I'm still trying to figure out.

Also, question about your example of modcon at 8K constantly running vs CI at 100K cycling, does that provide any different experience in the house? Would it feel like a more steady heat?

Hot_water_fan

@GroundUp I don’t think it’s fair to compare an old install to a brand new install. A new CI that thermally purges, has ODR, and isn’t wildly oversized shouldn’t be 30% behind a new modcon. I agree though that 30% vs an old boiler is possible. 

David_16

Hot_water_fan said:

@GroundUp I don’t think it’s fair to compare an old install to a brand new install. A new CI that thermally purges, has ODR, and isn’t wildly oversized shouldn’t be 30% behind a new modcon. I agree though that 30% vs an old boiler is possible. 

My options are Weil-McLain Eco Tec vs Weil-McLain CGa. I don't see anything about thermal purging for the CGa (or is that something that the installer pipes in?) and do I definitely want to push for an ODR? This installer came in with the Eco Tec which has the ODR, but I haven't asked him about the ODR for the CGa yet. More than one other company that I had out to quote CIs said ODR isn't particularly effective in this region and that they've had customers request they be taken out/disabled.

pedmec

you can't just use the price difference between a cast iron boiler and a mod/con boiler. There is way more to it than just the price of the boiler. When you install a mod/con the exhaust and air intake are all included in your install. When you install a cast iron everybody just thinks you dump the flue into the chimney and away you go. Total fiction. Where i am from you will need a chimney inspection to ensure it is safe and it can only be used as is if the new boiler is the same efficiency. And if it is deemed unsafe you will have to have a chimney liner install at an added cost. Then you need to make sure that you have enough air for combustion. Meaning wherever you install your boiler your mechanical room will need to be large enough to support combustion. You will need to meet the minimum room size requirements for proper combustion. if you don't meet those minimum requirements you will need to bring in outside air. most properties will not meet the requirement.

David_16

pedmec said:

you can't just use the price difference between a cast iron boiler and a mod/con boiler. There is way more to it than just the price of the boiler. When you install a mod/con the exhaust and air intake are all included in your install. When you install a cast iron everybody just thinks you dump the flue into the chimney and away you go. Total fiction. Where i am from you will need a chimney inspection to ensure it is safe and it can only be used as is if the new boiler is the same efficiency. And if it is deemed unsafe you will have to have a chimney liner install at an added cost. Then you need to make sure that you have enough air for combustion. Meaning wherever you install your boiler your mechanical room will need to be large enough to support combustion. You will need to meet the minimum room size requirements for proper combustion. if you don't meet those minimum requirements you will need to bring in outside air. most properties will not meet the requirement.

Chimney liner is already included in the CI cost that I have.  Combustion air I'm aware and have to ask about that tomorrow.  There's no extra air for my oil setup today, though that could be wrong.  One other installer said they could easily cut through the inside wall to the den to provide combustion air if required by the inspector. 

pecmsg

If you need combustion air get it from outside. Why waste the conditioned air?

David_16

pecmsg said:

If you need combustion air get it from outside. Why waste the conditioned air?

I assume it probably would be cheaper / easier to come through that wall than to go through an outside wall, but I still have to ask my particular installer what he would plan on doing and if that was included in his price or not. I will note a preference for outside air, if that's an option.

gyrfalcon

Outdoor reset is an option. 

David_16

gyrfalcon said:

Outdoor reset is an option. 

Yes but it is a worthwhile option in my region? Seems like more than one installer said it wasn't worth it for CI.  Not sure what the one I'm using feels yet since I was originally going to go the modcon route with him but may not do that anymore.

pecmsg

What’s your area?

David_16

pecmsg said:

What’s your area?

Long Island, NY

pecmsg

Yes outdoor reset is worth it. 

As is a heat pump. 

hot_rod

Some additional thoughts. I'd guess not many CI boilers ever run at the rated efficiencies. Certainly not zoned ones as the Cycle Efficiency is the determining factor. IF, and most are, the boiler is oversized then cycle efficiency goes down even more. We have done examples here where actual efficiency drops into the low 70% on zoned, oversized CI on fin tube systems.

Some suggestions, upgrade the envelop first. Even a weatherstrip upgrade can make a difference, as infiltration can rob a lot of your fuel $$

Next do a room by room heat load calc, followed by a fin tube assessment. How low of a SWT can you actually run will now become clear.

Next look up some 20 year weather data. How often are you at design, or below in your area? Probably 80% of the heating system you are below design. So 80% of the time the CI boiler, properly sized is oversized and cycle efficiency starts to chip away at the operating cost. Even on a single zone system!

The higher the temperature required at the fin tube the more loss through the wall to the outdoors. Fin running at 140 loses less through the wall build up, than a 180F system. A simple delta T formula.

So a mod con, properly sized, installed and set up, addresses all the efficiency robbing concerns.

It may modulate down to the lowest zone load. ODR keeps the SWT matching the heat load fairly accurately. Ramp delay, anti short cycling can be used if it is a micro-zoned system where small loads fall below the lowest turn down. These all come into play even if it never condenses!

Below is BIN data is for upstate NY, but I suspect the trends would be similar for L.I, as far as % of design. I believe 0 or 5 above is design in this upstate area.

If you can get SWT down around 150 or lower, design day, the mod cons will really sing fig 3-6. Mod con efficiency goes up as they run at low turn down, fig 3-31. Widen the operating delta to 30° to lower the return even more. It's the return to the boiler that dictates the condensing operation.

Also a slide from Viessmann training regarding reducing SWT and ODR usage. With a CI boiler you are limited on how aggressively you can set the ODR and protect the boiler from extended cold run time.

That leaves the question of maintenance cost, life expectancy. That will be debated till the end of time.

I started a file of mod con cleaning from IG, with poster permission. I've seen boilers that hadn't been serviced in 8 years looking very clean when opened. And boilers opened after one year 1/4 full of mouse turd deposits.
I feel intake air filter and proper burner set up the first year and a check after a year has a lot to do with the combustion side condition.

So it comes down to number crunching first, or talking with folks that have made the mod con transition on CI fin tube systems in your area, for some case study data

Daveinscranton

The information in the above slides is wonderful.  Perfect summary in words from Rod and accompanying graphics.

David_16

hot_rod said:

Next do a room by room heat load calc, followed by a fin tube assessment. How low of a SWT can you actually run will now become clear.

It may modulate down to the lowest zone load. ODR keeps the SWT matching the heat load fairly accurately. Ramp delay, anti short cycling can be used if it is a micro-zoned system where small loads fall below the lowest turn down. These all come into play even if it never condenses!

If you can get SWT down around 150 or lower, design day, the mod cons will really sing fig 3-6. Mod con efficiency goes up as they run at low turn down, fig 3-31. Widen the operating delta to 30° to lower the return even more. It's the return to the boiler that dictates the condensing operation.

That leaves the question of maintenance cost, life expectancy. That will be debated till the end of time.

So it comes down to number crunching first, or talking with folks that have made the mod con transition on CI fin tube systems in your area, for some case study data

This some great stuff and I appreciate the time to put this together! I'm still struggling with my decision here. When the modcon was $1000 less to install, it would have been a lot easier decision, but with the gas co rebate gone, it's a harder call.

I do have heating 2 zones, but 1 zone I have set nearly permanently to 63 degrees and it doesn't come on much at at all.

One concern regarding the modcon is that I know have 2 bedrooms with likely less than adequate baseboard so would lower temp water make things even worse in those rooms on a cold day? If the modcon, set to run efficiently, isn't going to properly heat those rooms, that's an issue. Sure, I can fix/add to the baseboard in those rooms or not have the water temp go so low, but then spending more $s.

What it really comes down to though is the cost of ownership vs the savings. I'll probably be in the house another 15-25 years, but I'm somewhat comfortable not considering the life expectancy of the unit itself because who really knows that. So then it's the cost of maintaining each system annually vs the oil savings. Let's say I'd spend $2000 in heating costs with a new gas CI and maybe modcon saves me another $250/year? I know it's just an estimate, but can't really figure out a way to come up with a real number. In all honesty, I'm definitely guilty of not always staying with a proper maintenance plan with other things so the idea of something that requires less maintenance appeals to me. I would say I have a very clean boiler room. Maybe with the modcon I have to have someone come every year at $350/visit (or can I get away with every other year or so service), but with the CI, maybe I would have someone come every 3 years at maybe $250/visit (since there are way more companies I could choose from to service the CI). That's $800 more servicing every 3 year period vs 750 in gas savings, pretty much a wash. Plus, I think I'm more likely to need a semi-costly repair with the modcon (like if a piece of electronics goes).

Am I somewhat on target here? If the annual gas savings could really be closer to $350 or more, that changes things a bit.

hot_rod

Yes you can be handicapped in boiler replacements. If one room is under radiated with the CI boiler running, even at 180, that is not the boilers fault. You decide if it is worth upgrading that room(s). Sometimes you can close down dampers on the warm rooms and push more heat into under radiated rooms, a balance attempt. Depending on how the loop is piped.

And you are correct with the two biggest unknowns, fuel costs going forward, and maintenance or repairs over the 15- 20 life expectancy.
I'm of the opinion 20 years is reasonable for a quality brand, properly installed and occasionally serviced mod con.

I think comfort level goes up with a properly dialed in mod con, running long efficient cycles and maintaining accurate room temperatures. If you can put a dollar amount on that?

Most often on a site named Heating Help, we see failed systems not so much the ones that work properly, efficiently and reliably for 15- 20 years

I think all CI boiler manuals suggest occasional, maybe yearly clean and checks, but I doubt that happens often unless you have a service contract. CI, being lower tech handle neglect or abuse much better.

Tough call, but you have the correct info needed to make the best decision, for your home.

A pic from Ted, a longtime Viessmann person.

David_16

hot_rod said:

Yes you can be handicapped in boiler replacements. If one room is under radiated with the CI boiler running, even at 180, that is not the boilers fault. You decide if it is worth upgrading that room(s). Sometimes you can close down dampers on the warm rooms and push more heat into under radiated rooms, a balance attempt. Depending on how the loop is piped.

I think all CI boiler manuals suggest occasional, maybe yearly clean and checks, but I doubt that happens often unless you have a service contract. CI, being lower tech handle neglect or abuse much better.

Tough call, but you have the correct info needed to make the best decision, for your home.

As far as the under radiated rooms, CI with no outdoor reset will always heat those rooms with 180 degree water and that will be (has been with current boiler) just fine enough. But if modcon tries to heat those rooms with 150 degree water, might those 2 rooms feel colder than the rest of the house?

And then one last go around on the annual maintenance. If I'm a lazy homeowner trying to save money but would like the system to last and have a clean boiler room, what kind of preventative maintenance is really needed for each? Do I really need someone to come look service the modcon annually or could I get away with every 2 or 3 years? For the CI, could I get away with someone coming every 3 or 4 years? If I can get a handle on this piece, I think that's the last part of the equation and then it's just making the call.

hot_rod

You design the system for the max. temperature at design condition, the coldest day of the season for example. Anytime you are below design, the boiler SWT can be reduced. The boiler ODR control does the calculation on this. Some boilers include a "boost" function. If the boiler SWT have not increased after a period of time it steps up the modulation rate to catch the load.

I'm on my 6th or 7th mod con in the various homes and buildings I have owned. Dating back to the MZ, Munchkin era of the 1980's. I have never done a yearly service on any of them. In one case I opened a Teledyne Laars Mascot 6 years after I installed it. Not proud of that

My thought is to open it for a clean and check after the first season. If it is clean inside like the one shown above, I would let it go 2 or 3 years and check it again.

Do you take your car or truck in for $$5000 mile interval service, as per some manufacturers requirement?

Usually a system with bad combustion, for whatever reason, shows up the first season. Some homeowners on this list do their own service, invest in a entry level combustion analyzer perhaps. It's not rocket science. Attend a factory or rep training on how to service your model. That is how we all learn to do a proper service and adjustment.

Pollen, dusty air, crappy LP, mis-adjusted burner, contaminated intake air from inside the building, recirculated exhaust are some of the reasons boilers combustion chambers fill with junk. In most cases this can be prevented.

David_16

hot_rod said:

You design the system for the max. temperature at design condition, the coldest day of the season for example. Anytime you are below design, the boiler SWT can be reduced. The boiler ODR control does the calculation on this. Some boilers include a "boost" function. If the boiler SWT have not increased after a period of time it steps up the modulation rate to catch the load.

I'm on my 6th or 7th mod con in the various homes and buildings I have owned. Dating back to the MZ, Munchkin era of the 1980's. I have never done a yearly service on any of them. In one case I opened a Teledyne Laars Mascot 6 years after I installed it. Not proud of that

My thought is to open it for a clean and check after the first season. If it is clean inside like the one shown above, I would let it go 2 or 3 years and check it again.

Do you take your car or truck in for $$5000 mile interval service, as per some manufacturers requirement?

Usually a system with bad combustion, for whatever reason, shows up the first season. Some homeowners on this list do their own service, invest in a entry level combustion analyzer perhaps. It's not rocket science. Attend a factory or rep training on how to service your model. That is how we all learn to do a proper service and adjustment.

Pollen, dusty air, crappy LP, mis-adjusted burner, contaminated intake air from inside the building, recirculated exhaust are some of the reasons boilers combustion chambers fill with junk. In most cases this can be prevented.

I will use every 2-3 year maintenance in my calculation then.

Ok, Weil McLain Eco Tec 110 with WM indirect it is. Done! I think it was just killing me that the $1100 rebate from the gas co that I could have received for an install a few days ago is now gone, but it's gone and there's nothing I can do about it and have to make the decision without considering that.

I think the installer may include the first year or 2 check up, which sounds like that would be helpful, but I'll have to confirm that. Currently, I have an oil boiler and I would say, even with that, the boiler room is very clean with good quality air. I even store an old computer in there.

You guys are great, thanks everyone!

hot_rod

There may be other incentives and rebates still available. Federal, State, local utilities, etc. If you have time to wade through all the options here.
wwwdsireusa.org

David_16

hot_rod said:

There may be other incentives and rebates still available. Federal, State, local utilities, etc. If you have time to wade through all the options here.
wwwdsireusa.org

I will review. Local gas co rebate of $1100 is gone, I've confirmed that through multiple channels. I should still qualify for $600 federal tax credit, which I had already included in my math. Will see if anything else might be available that I haven't yet uncovered.

David_16

Figured I'd circle back around here now that I have more data.

I had a Weil McLain Eco Tec 110 with Weil McLain indirect installed in late January. My first full month gas bill was $184. I don't have a great history of my previous oil usage, but there's no way I would have used less than 3.5 gallons per day with this year's Feb temps. I was locked in at $4/gallon so that's $420. Even if oil dropped to $3/gallon, that's still $315, but the 3.5 gallons per day is probably on the low end. I'd estimate over time, with fluctuations in oil pricing, I've got to be in the ballpark of 50% savings over oil.

Still no idea what I would have realized with a gas CI, but I bet not nearly as much. This boiler runs at about 60% when it's heating up and then around 20% to maintain. I probably rarely condensed in February.

Jamie Hall

Just one comment. On efficiency. I was -- very strictly -- comparing apples to apples. That is, a properly set up, controlled, and maintained, non-condensing boiler with an equally well set up, controlled, and maintained, condensing boiler. I was NOT trying to take into account vagaries in the rest of the system. In that circumstance the. non-condensing boiler -- or the condensing boiler operating above the condensing range -- should have a running efficiency of around 84%. Under the same conditions, assuming fully condensing (100 degrees or below stack temperature) the condensing boiler will reach a maximum efficiency of 96%.

There are a Lot of factors which can and will drive the overall yearly efficiency of either type of boiler well below those figures.

As it says in the advertising -- your mileage may vary.

LRCCBJ

The calculated combustion efficiency of the boiler itself is only one factor in the system efficiency. It completely neglects the benefits of modulation of a mod-con, completely neglects the benefits of reduced SWT and it absolutely neglects the massive energy that a CI boiler loses to the the typical basement.

To simply quote it repeatedly does the readers of this site a disservice as those numbers are not what occurs in the real world.

David_16

LRCCBJ said:

The calculated combustion efficiency of the boiler itself is only one factor in the system efficiency. It completely neglects the benefits of modulation of a mod-con, completely neglects the benefits of reduced SWT and it absolutely neglects the massive energy that a CI boiler loses to the the typical basement.

To simply quote it repeatedly does the readers of this site a disservice as those numbers are not what occurs in the real world.

I think this is exactly my case. If I went from oil CI to gas CI, maybe the gas CI is 5% more efficient than my old oil CI, plus the cost savings of gas vs oil and that's going to be pretty close to what savings I'd see. Modcon changes the equation completely and it seems as if I'm realizing around 50% savings.

LRCCBJ

David_16 said:

I think this is exactly my case. If I went from oil CI to gas CI, maybe the gas CI is 5% more efficient than my old oil CI, plus the cost savings of gas vs oil and that's going to be pretty close to what savings I'd see. Modcon changes the equation completely and it seems as if I'm realizing around 50% savings.

Back in 2015, I installed a mod-con for someone who had an old five section CI oil fired boiler with a tankless coil. They were going through $5K/year in oil. The mod-con reduced this to under $1500 at the time. Gas was significantly less costly than oil (50% from memory) and the mod-con system efficiency was 40% better than the oversized CI. They were astounded.

Hot_water_fan

The calculated combustion efficiency of the boiler itself is only one factor in the system efficiency. It completely neglects the benefits of modulation of a mod-con, completely neglects the benefits of reduced SWT and it absolutely neglects the massive energy that a CI boiler loses to the the typical basement.

To simply quote it repeatedly does the readers of this site a disservice as those numbers are not what occurs in the real world.

I hear you, but apples to apples should be modcon vs. a properly set up new CI. That new CI should be: 1. appropriately sized 2. include an ODR 3. use thermal purge 4. be combusting correctly, so the gap will close a bit. Not all the way, but should be closer to a modcon than an old CI.

Jamie Hall

LRCCBJ said:

David_16 said:

I think this is exactly my case. If I went from oil CI to gas CI, maybe the gas CI is 5% more efficient than my old oil CI, plus the cost savings of gas vs oil and that's going to be pretty close to what savings I'd see. Modcon changes the equation completely and it seems as if I'm realizing around 50% savings.

Back in 2015, I installed a mod-con for someone who had an old five section CI oil fired boiler with a tankless coil. They were going through $5K/year in oil. The mod-con reduced this to under $1500 at the time. Gas was significantly less costly than oil (50% from memory) and the mod-con system efficiency was 40% better than the oversized CI. They were astounded.

Oh whatever. Let's look at this example again. We have an old oil fired boiler, with unknown maintenance history and adjustment. And we replace it with a brand new gas fired mod/con. And gas is half as expensive as oil at the time. And the savings are attributed entirely to the wonders of the mod/con?

I'm sorry. I'm sure the mod/con did save money -- but to attribute that, even by implication -- solely to the mod/con is false. Half the savings were from the change in fuel. How much of the extra cost of running the old oil boiler was due to poor maintenance and adjustment? I can drop the efficiency of an oil -- or gas -- burner from 8% to 60% in ten minutes with a screw driver and a crescent wrench. And the customer would never be the wiser.

Years ago I worked at a gas station back when gas stations also did service. A neat trick I saw (I never did it!) was to loosen a spark pug wire while checking the oil. Then when the poor sap came back complaining o9f an misfire sell them a full scale tuneup.

If you are going to sell something, sell it honestly. Mod/cons are excellent in many applications, and can, properly installed and adjusted, save some energy. No question. But comparing the wonders of a new mod/con to an ancient CI...

LRCCBJ

Hot_water_fan said:

I hear you, but apples to apples should be modcon vs. a properly set up new CI. That new CI should be: 1. appropriately sized 2. include an ODR 3. use thermal purge 4. be combusting correctly, so the gap will close a bit. Not all the way, but should be closer to a modcon than an old CI.

Agreed.

However, the point is that you simply cannot compare the combustion efficiency of the mod-con to the combustion efficiency of a new, properly installed CI and make the conclusion that this will be the energy savings between the two choices. Some on this site perpetually wish to do that and come up with a result of not more than 11%. This is false.

The brand new CI still suffers from typically elevated SWT, still suffers from huge jacket losses to its environment, and still suffers from the inability to modulate. These variables will affect the overall system efficiency of the brand new CI and will absolutely change that 10% combustion number to a value that is over 20% every single time.

It is also disingenuous to make the conclusion that every single CI boiler that is replaced is running at 60% combustion efficiency. The writer has no idea what the combustion efficiency is and it could very well be 80%.