Please help me design a new heating system!

[Jadnashua]

None of the above:
- no tile on top of a hardwood; the hardwood changes shape too much with the seasons - the hardwood should come out entirely. You don't want to install tile on top of planks, either...you want a layer of plywood on top of them.
- unless you want the height, 1/2" cbu is a waste on the floor; 1/4" is fine
- a mudbed over wood needs to be nominally 1-1/4" thick...1/2" is WAY too thin

A membrane like Ditra is much easier to install than cbu and gives better isolation than cbu.

 

[Gnfanatic]

Jim, thats for the response I know I cannot put tild over the wood floor. Under the wood floor is a subfloor (obv). My subfloor consists of 3/4 thick plank wood (I am thinking oak). IF I put 1/2 cbu over that and then tile over that it would be leveled with the wood floors in the bedrooms. So mud is out of the question becuase 1/2-3/4 is to thin. My question to you is ditra seems to be a very thin/soft material. The site states that if you have a plank floor you need another layer of plywood over that then install ditra. Would it feel and be more solid if I use 1/2 cbu instead of 1/2 plywood?? I want to do this one and I truly appreciate you guys patience on this post.

thanks!!

 

[Sponsor]

 

[Jadnashua]

You don't want ANY hardwood in your subfloor with tile on top of it. CBU is not considered structural, it's quite brittle, so for practical purposes, on a floor, thickness doesn't matter or count for strength. It's only purpose is to provide a good substrate for tile. You need a layer of ply on top of planks, and I wouldn't risk it if they are hardwood. Softwood, okay. It's not a strength issue here (the hardwood is stronger), it is a seasonal movement issue - the hardwood just moves too much.

Plus, screwing or nailing cbu down where there's hardwood underneath will likely cause tenting and be a major pain to install. Remember, the goal is 100% support under the tile - the thinset under the CBU provides that if done properly, but you need to anchor it to the subfloor, and it would be really tough if there's hardwood under there, regardless of the fact that it moves too much.

If you need height, thicker cbu is okay, but additional ply adds strength. I'm a fan of Ditra - easy to cut, easy to carry, thinner, and provides more decoupling than cbu. if you haven't done it, the large quantity of screws (or nails if you want to use them on a subfloor) can be a major pain to get down. If you use nails, for a non-pro, since they don't get recessed like a screw, it's more of a pain to spread the thinset. With the screws, if you're off a little, the head can be high (if you use them, get the ones with the square drive head...less likely to strip the head when driving them in).

Don't obsess over trying to keep the levels between rooms exact...transitions are not a big deal if done right, and are easy between tile and hardwood.

 

[Gnfanatic]

Thanks Jim, my planks are def soft. I will use plywood instead of the cbu. I will order Ditra next week from tilexperts in NJ. Quick question for ya. 1/2 inch ply or 3/4?

 

[GrumpyPlumber]

I only skimmed this thread, so some details have likely gotten past me.

I saw mention of a budget of $6k, with a desire to install a Buderus.
The Buderus alone will cost about $3,500 for the GB 125 (most likey the model for a 1600 sq/ft home) alone.

Circ's, relays, copper tubing (required copper manifold with Buderus) and overall miscelleneous parts for radiant loops will as much as double that.

I also noticed the mention of Keyspan (now Nat'l grid, services MA, NY, NJ) it looks like you'd like to attempt to tackle this install yourself, Keyspan won't turn on the gas unless it's being done by a licensed plumber or gas fitter.

As for cost justification -
Your big savings will come from the simple coversion from oil to gas regardless how efficiant the boiler is, you'll likely save big.

A gallon of oil is the equivalence to 1.4 therms (CCF) of Nat. gas, at a current price of $1.80 per therm vs $4 a gallon of oil, do some math.
The gas equivalence is about $2.50.

The Burnham gets 85% as opposed to the Buderus's 95%, which is CONDITIONAL that the Buderus operate at a temperature of 140.
Standard baseboard heat would not have reasonable enough recovery at that temperature.

That 10% difference is looked at in terms of fractional...you'd have a tenth the efficiancy increase with a buderus over a Burnham SCG to justify a price difference from $900 to $3500...ONLY if you invest the added money for radiant floor heat and add heat exchangers with seperate circ's and the added manifolds.

Your $6k budget is shot, for stock alone.

I have to mention that I think you may be underestimating the value of the cost vs savings in this case, as well as the potential difficulty involved in the work.

You may want to call Keyspan (nat'l grid) before you make further plans on budget, I doubt they'll allow you to do this yourself without a licensed pro.

The heat portion of the job could theoretically be done by you, but the boiler, the gas and meter connection cannot be done by anyone aside from a licensed guy.

Also, be mindful that the MFG warranties are void when not installed by a professional.

 

[Gnfanatic]

Grumpyplumber, thansk for the excellent post. I am looking at the Weil-Mclain ultra series unit and a in-direct. I do know that Keyspan wants a lic plumber. My idea was to do all the work (raidiant,baseboards,elec,run all the lines etc) and get a lic plumber to connect gas and meter. I am single guy and make so much, I cant afford to hire a crew to do it.
"That 10% difference is looked at in terms of fractional...you'd have a tenth the efficiancy increase with a buderus over a Burnham SCG to justify a price difference from $900 to $3500...ONLY if you invest the added money for radiant floor heat and add heat exchangers with seperate circ's and the added manifolds".

Interesting stuff, so that 10% difference costs me an extra $3000. Sometimes i wonder if it is worth going for the ultra effecient units with such a small house? BTW, the baseboard's in the bedrooms are cast iron. I dont know wwhat temp they need to run at but I always ehard they are more effeient then the reg base board rads.
Grumpyplumber, what state are you located in that you know keyspan well?

thanks!

 

[GrumpyPlumber]

Gn, I'm Mass.
You NEED to call plumbers asap.
You've made an assumption that will likely land you disappointment.

I'll be honest, if you were to call me and say you'd done all the work & just want me to get the inspection..I probably wouldn't get back to you...most won't hold themselves liable for your work, nor risk being caught allowing someone else to work on their license.

In your situation, I'd go well out of my way to talk you out of anything extravagant with the budget you mentioned...the amount you save percentage wise is trivial when you do the real math in lieu of your circumstance.

A Buderus functions at 95+% efficient when run at 140 or less, you already mentioned you need to heat a portion of the home with radiators, so now you're running it at 160, which will still give you a slower recovery time.
You'll be running at about 90% to 92% efficient at that temperature.

Thats 5% better than the $900 boiler.

If your heat bill comes to $1200 a year, a 5% difference comes to $60.

The boiler, stock and labor your getting into will add thousands to your stock bill alone, not to mention the amount of work is substantial.

IF you had a gas bill of $5k per year, it might be worth the payoff...but I doubt you fit in that category, especially NOT with a $6k budget.

Also, missed this detail...you said you were converting from steam heat w/oil.

Is the current radiator system a one, or two pipe system?

If it's a one pipe, you are into major repiping, to the extent that a steam replacement with gas might be a better option price wise.

You really need to have the whole situation scoped by a pro.

My impression is that you're getting "swiss cheese" info...and interperetting a convenient outcome based on relatively few parameters...please think these things through before you dig a hole, talk to a pro and get some realistic idea's in real life.

 

[Gnfanatic]

grumpy. thanks again. I had a single pipe system with the radiators in the walls.The system was very old and there was no insualtion behind the rads (obv). So I removed the pipes and the rads, insulated the walls and closed the holes up. Yes, things are getting confusing on what path to take. I will call some plumbers during the week and make some appointments. I gaurantee I will have 10 diff designs, 10 diff amounts and all that good stuff. Looks like I am going to skip the exp boiler and go for Keyspans deal. I get 40% off at blackmans so that obv helps buying the stuff. I will see what the plumbers have to say. I still would rather do it myself.

 

[BigLou]

Grumpy,

gota disagree with your premise that a 10% gain in efficiency is a 10% savings. A HE boiler will modulate as well as operate at a higher efficiency. On a warm day(40 degrees) you not only get 95% efficiency if you set it up right but you avoid short cycling and only make the amount of BTU's you need. This is where the real savings come in If the unit is slightly undersized it will almost always operate at peak efficiency

Its a lot like how your driving habits can affect your fuel mileage

Most standard boiler efficiency ratings are overblown and in reality are in the high 70% range. as I recall they use a delta T of 40 degrees to rate that we both know thats not real world.

Whats a G125 ? I see a GB124 and thats not their high efficiency model.

I went from a standard oversized oil boiler using 1350 gallons/year to a GB142 and my gas bill for the year is a hell of a lot less then $1200 maybe $800 tops and my house is poorly insulated.

Too bad he got rid of his old radiators they would have worked perfectly with a new HE boiler run 110 degree water through them 24/7 and watch the savings pile up

I think before you tell some one they are only going to save $60 you should get your facts straight. The actually savings will be a lot more

Lou

 

[GrumpyPlumber]

Lou,
My facts were straight, read again..I wasn't comparing oil to gas in that 10% figure.
You didn't read it all.

Read it, I said switching to a gas boiler with the same efficiency as the old oil boiler will save him at least 30% off his fuel bill and his old oil burner is likely operating closer to the 70% mark. (Therm to BTU per gal comparison...read it)

The 10% figure was a rough figure ONLY comparing the two types of GAS boilers.

I have two individual customers from last summer that have given me copies of their gas bills since last summer and the previous year.

Both were gas before replaceing the boilers.

One was a Buderus, the other a Burnham SCG (85%)

The Burnham has saved my customer MORE money than the Buderus.

Why?

The Burnham customer has a massively larger bill, but more importantly the comparison is for a boiler that was literally falling apart.

His gas bill has come down 40% over the year, with no DHW.

The buderus customer has a newer home, heavily insulated and his old gas bill was about $1200 a year.
The boiler I replaced wasn't quite as old, he just wanted to decrease his "carbon footprint".

His gas bill has come out to 25% less over the year, with DHW.

These comparison were figured by THERM useage, NOT the actual bill, as gas prices have increased.

Your situation was unquestionably an old oil boiler burning at extemely low efficiency as well as being oversized ...you were basically heating the sky above.

Peeked on the Buderus site, and it appears the model #'s have changed.

I believe one of this sites moderators has a 125, maybe he'll correct me, but for the point it's splitting hairs.

Do a web search for the 125 and you'll see them on sale on auction sites.

You're right, he should NEVER have removed any piping, BIG mistake.

Your boiler running at 110 is definitely going to optimize it's performance, you're getting the full 95.9% efficiency, but at that temperature you're either already piped for radiant floor heat or you live in a southern state.

If you attempt to run a boiler at 110 for standard radiator or baseboard heat, you'll definitely get 95%, but you'll be running MUCH more frequently to try to heat your home as the boiler tries to keep up.

THIS is what I meant by "swiss cheese", you CANNOT run a boiler at 110 in the northern states and get reasonable recovery in the colder months on radiators.

That temp works on radiant floor with the larger area coverage.

Gn has radiators (some that he removed, unfortunately), he's in my area of the country where it gets very cold in the winter.
He has a budget of $6k and would have to add a fairly complicated heat exchanger set-up to get the floor temps down to 110-130 yet still be able to keep the existing radiators operating at a feasible temperature.

Lou, get your facts straight.

 

[NHmaster]

Let's try to clarify a couple things. You said the house had steam heat? so it's an older house I assume. Then you want to put radiant piping in a few rooms in conctrete so I am assuming that you are or have stripped the house down to the framing? And you have existing CI base in a couple bedrooms?

Lets start at the start so to speak. # 1, you are going to need a design professional to come out and heat loss the house first. This is vital, especially with radiant heat. As nice as radiant is ( I have it in my house) It does not react rapidly to tempreture changes and it can not supply the same btu\hr that baseboard and radiators can. I'm betting that if this is an old house, you will more than likley require supplimental heat in the radiant zone. Either baseboard or radiators or even toe space heaters.

#2 Balancing loop temperatures. The in pour radiant will take slightly higher temps than say an in slab loop would take, but still signifigantly lower that the Baseboard loops. That means primary secondary piping or hydronic separator ( I prefer) and either a tempering valve or an injection circulator for the radiant loop, along with the appropriate floor sensor. ( I like Tekmar )
Loop pipe sizing and spacing can only be done properly by designing from the heat loss\load calculations. 1/2" os normally used but occsionally 5/8 may be required.

#3 Cost. With a new boiler (anybodys) piping, valves, controls and misc. stuff you are looking at at least $ 7,500.00 for the materials alone and around 15 to 20 grand to have the system installed.

You are in Mass so Grumpy is correct, you can't get the sign off without a license. Pretty depressing Huh? If I were you, I'd drop the radiant idea. Put in a fairly high efficiency gas boiler (you pick- go on web-investigate) and put baseboard back in along with a boiler temp modulating control. (Tekmar) Radiant heat is not necessaraly more efficient, just more comfortable.

 

[BigLou]

Lou,
My facts were straight, read again..I wasn't comparing oil to gas in that 10% figure.
You didn't read it all.

Read it, I said switching to a gas boiler with the same efficiency as the old oil boiler will save him at least 30% off his fuel bill and his old oil burner is likely operating closer to the 70% mark. (Therm to BTU per gal comparison...read it)

The 10% figure was a rough figure ONLY comparing the two types of GAS boilers.

Grumpy I did read it and I disagee that a 10% increase in efficiency equates to a 10% decrease in fuel bills. If that is all you get you don't have the thing programmed correctly. I agree that gas is much less costly per BTU then oil also a lot cleaner and more reliable.

I have two individual customers from last summer that have given me copies of their gas bills since last summer and the previous year.

Both were gas before replaceing the boilers.

One was a Buderus, the other a Burnham SCG (85%)

The Burnham has saved my customer MORE money than the Buderus.

Why?

The Burnham customer has a massively larger bill, but more importantly the comparison is for a boiler that was literally falling apart.

His gas bill has come down 40% over the year, with no DHW.

The buderus customer has a newer home, heavily insulated and his old gas bill was about $1200 a year.
The boiler I replaced wasn't quite as old, he just wanted to decrease his "carbon footprint".

His gas bill has come out to 25% less over the year, with DHW.

These comparison were figured by THERM useage, NOT the actual bill, as gas prices have increased.

What kinda buderus ? I am talking about the GB142 capeable of 98% efficiency if set up right and allowed to modulate. Running almost all day at a low water temp if highly efficient. Modulating boilers are great for this sort of application as they can always raise the water temp as demand dictates.

Your situation was unquestionably an old oil boiler burning at extemely low efficiency as well as being oversized ...you were basically heating the sky above.

Old and oversized yes but not any more or less then anything else out there today. All non modulatiing boilers are oversized for the application 99% of the time

Peeked on the Buderus site, and it appears the model #'s have changed.

I believe one of this sites moderators has a 125, maybe he'll correct me, but for the point it's splitting hairs.

Do a web search for the 125 and you'll see them on sale on auction sites.

Model numbers do make a big difference, try ordering parts or supplying a customer with the wrong model number and see what happens. the GB124 is a standard replacement model, the GB142 is a modulating condensing model BIG DIFFERENCE. maybe we are comparing apples to oranges here .

You're right, he should NEVER have removed any piping, BIG mistake.

yes always get a good design in place before you do any demo saves a lot in the long run. My system was designed by a licensed plumber who also has a batchlors degree in Mechanical Engineering and is working on his PE stamp.

Your boiler running at 110 is definitely going to optimize it's performance, you're getting the full 95.9% efficiency, but at that temperature you're either already piped for radiant floor heat or you live in a southern state.

If you attempt to run a boiler at 110 for standard radiator or baseboard heat, you'll definitely get 95%, but you'll be running MUCH more frequently to try to heat your home as the boiler tries to keep up.

Ok perhaps I miss represented my self here and I want to say I am sorry. I can run 110 water but not all winter long and I don't live in a southern state. I do however manage to spend at least 80% of my running time in condensing mode. I can do this because I have way to much steel fin tube baseboards left over from the old oversized system. I do not have in floor radiant yet. Perhaps you are of the old school but with my HE systems long run times are not a problem they are desired for them. They respond to demand by increasing output temp not run time. This is where Mod/Con boilers justify thier cost. Making 85,000 BTU when the home only needs 35,000 is a waste talk about heating the sky.

THIS is what I meant by "swiss cheese", you CANNOT run a boiler at 110 in the northern states and get reasonable recovery in the colder months on radiators.

I agree with the swiss cheese info and that you can't always run 110 degree water but I would wager you could keep that radiator at 110 50% of the heating season and have a comfortable room . What does recovery have to do with it ????? comfort is attained by keeping the room a constant temp, not by letting it swing up a down. My buderus even has a setting for CONSTANT CIRCULATION.

That temp works on radiant floor with the larger area coverage.

Gn has radiators (some that he removed, unfortunately), he's in my area of the country where it gets very cold in the winter.
He has a budget of $6k and would have to add a fairly complicated heat exchanger set-up to get the floor temps down to 110-130 yet still be able to keep the existing radiators operating at a feasible temperature.

Lou, get your facts straight.

My facts are straight
We agree again that $6k is unrealistic unless he has a licensed plumber who will do it for free like I did. The mixing valve is close to a grand alone last time I checked, however if you make the whole house radiant one is not needed with new mod/con boiler because you can set the temp in the boiler to only be 130 degrees tops. Its also not nearly as cold around here as you make it sound. I live in western Massachusetts near springfield where do you live ? I want to say the average day time temp is like 35-40 degrees in the middle of winter. Its new worthy when we have more then five days in a row below freezing. I would still want heat at 35 but its not nearly the damnd on the 1-2 nites a year when it drops to 10 below. This is a common design temp around here that leads to the majority of the systems being oversized

I respect all your experience and knowledge but I think maybe you need to go back to school and learn the new way of things.

Lou

 

[NHmaster]

I guess we can all agree that this job can't be done for 6 grand, yes? So what's this poor fellow to do? His house is torn apart, It's August with September on his door step, he has no heat and only 6 grand in his pocket. In my opinion his only option is to put an non condensing high efficiency gas boiler in and run baseboard in the house. You can spend a whole lot of money chasing after the highest efficiency but you will pay a premium for every efficiency point gained. Most often to the point of no return. It makes no sense to spend 20 grand on a system that has a 20 year return. Who's to say the system will even be viable in 20 years?

 

[BigLou]

I guess we can all agree that this job can't be done for 6 grand, yes? So what's this poor fellow to do? His house is torn apart, It's August with September on his door step, he has no heat and only 6 grand in his pocket. In my opinion his only option is to put an non condensing high efficiency gas boiler in and run baseboard in the house. You can spend a whole lot of money chasing after the highest efficiency but you will pay a premium for every efficiency point gained. Most often to the point of no return. It makes no sense to spend 20 grand on a system that has a 20 year return. Who's to say the system will even be viable in 20 years?

I guess thats a good of a solution as any. But I still think he is better off with the best boiler he can afford even if its hooked up to baseboard Gas aint going to get any cheaper

Lou
PS
how did I get an avatar ?

 

[GrumpyPlumber]

Lou, yes, the Buderus can be set to operate conditionally for BTU output.
However, there is no "non-condensing" mode...it's always condensing.
If not, yer in deep doo-doo when the plastic exhaust pipe gets hit with it.

It modulates based on delta T & exterior temperature sensor.

READ your MFG manual, the efficiency may go up if you run the boiler to max at 110, but the boiler runs longer, that means it eats gas while running, thats not calculus there.
The in depth technique to adjusting the temperature is in the "hidden" control panel on that hard to see knob the displays the temp settings in BOLD type, real mechanical stuff there.

You stated you had been using over 1300 gallons of fuel oil and went to an $800 gas bill.

Add that up, a gallon of oil has the same BTU output of 1.4 therms, I think you maybe meant 1300 dollars(?)

1300 gallons would be a $5k+ fuel oil bill, a far stretch with a current gas bill of $800.

So, you're new Buderus is 7 times more efficient eh?
That means your oil boiler was operating at around 14% efficient...but then, my calculus is rusty, gotta grab a team of engineers for dat one.

I betcha you know how to tweak that bad larry to get the gas co to pay you back...huh?

All things aside, with you being the expert and me just grabbing at straws...I'd just like to get back to the purpose of my interjecture here:

well with only 6K that kinda limits you.
1)I think you should buy the highest efficiency boiler you can afford. I recomend buderus.
2) what kinda tank ? an inderect fired hotwater tank is a must
3) what exactly are you trying to do ? there is a lot more to it then just pick a size also concrete is the worst medium for radiant are you adding this in an addition ? how were the rooms heated before hand ? maybe forego the radiant now and buy a better boiler

Lou

I get silly there sometimes and recommend cheaper boilers when the budget is that low.
But, I apparently need some schoolin'.

I wonder at what point he realized he had the budget and built up the courage to rip out all those pesky radiators?

Oh, I guess it looks like Gn is in good hands here, maybe I oughtta just back out and let you do the advizin'...silly me, pardon the interuption.

Hope his wiring can handle the space heaters this winter.

See, you and I can chuckle at the funny repartoire, it's all in fun as we exchange snyde comments.

I am curious about how much chucklin' our friend is doing right now though.

 

[BigLou]

Grumpy,
I can see how you got your name, tell me where in MA you are and I will take you out for some coffee and try to put you in a better mood.

I stand by my statement that GN should do the best he can for the money what ever that may be.

Your wrong about the always in condensing mode sorry but unless you can explain to me how you are going to get a 45 degree change in temp when running at `180 its not condensing plain and simple. it has a max exhaust temp of 155 so how does it do that and have 135 degree water ?

you adjust the line that determines the temp on the AM10 module not the knob on the slide out control panel just so you know, you do have to take the cover off.

By my math the old unit was about 35-45% efficient due to lots and lots of short cycling. I know you may not understand this but short cycling is the enemy, on a 15 minute cycle I bet about 25% of the energy goes to heating up the system NOT HEATING YOUR HOME. sounds like a waste to me

I don't see the problem with it sipping gas for longer time periods its still more efficient the using lots and lots of gas for a 10-20 minute run time. I think you are just set in your ways and afraid of change

People like you who refuse to learn and change are why we can't move forward in this country. I know your a licensed plumber and I am not but that still does not mean your right. maybe its time to teach the old dog some new tricks

Sorry if i am sounding disrespectful and poking jabs at you. I do respect you for all you experience and knowledge and the coffee offer is for real. But just because you have been at this as long as I have been alive does not make you always right. If you have not been at this at least 27 years I appoligize for calling you old

Lou

 

[GrumpyPlumber]

Lou, you hook this fella up.

You offered the great advice on how $6k would do it.

Get him out of this jamb.

You can entice me into a really productive debate on why the Buderus condenses and why your a better thumb wrestler too while your at it.

Problem not resolved.

You gave him the go ahead with a $6k budget to buy a $3,500 boiler and install radiant.

He effectively proceeded to remove his current heating system & rip apart his home in full confidence.

Condensing, by the way, refers to the exhaust...the heat removed from the expelled gas is so great that it causes vaporized liquid to re-condense, you just made the argument.

Steam is created at 210...think, think hard.

Buderus's max temp is 196 for the DHW, by the way.

 

[GrumpyPlumber]

Grumpy,
I can see how you got your name, tell me where in MA you are and I will take you out for some coffee and try to put you in a better mood.

I stand by my statement that GN should do the best he can for the money what ever that may be.

Your wrong about the always in condensing mode sorry but unless you can explain to me how you are going to get a 45 degree change in temp when running at `180 its not condensing plain and simple. it has a max exhaust temp of 155 so how does it do that and have 135 degree water ?

you adjust the line that determines the temp on the AM10 module not the knob on the slide out control panel just so you know, you do have to take the cover off.

By my math the old unit was about 35-45% efficient due to lots and lots of short cycling. I know you may not understand this but short cycling is the enemy, on a 15 minute cycle I bet about 25% of the energy goes to heating up the system NOT HEATING YOUR HOME. sounds like a waste to me

I don't see the problem with it sipping gas for longer time periods its still more efficient the using lots and lots of gas for a 10-20 minute run time. I think you are just set in your ways and afraid of change

People like you who refuse to learn and change are why we can't move forward in this country. I know your a licensed plumber and I am not but that still does not mean your right. maybe its time to teach the old dog some new tricks

Sorry if i am sounding disrespectful and poking jabs at you. I do respect you for all you experience and knowledge and the coffee offer is for real. But just because you have been at this as long as I have been alive does not make you always right. If you have not been at this at least 27 years I appoligize for calling you old

Lou

Lou, I'll buy the coffee and you can throw it in my face if thats what it takes for you to see my point.

The guys home is in pieces, he has no heat, a short supply of money, and summer is almost over.

I understand the "feel good" intentions of helping someone out with your personal experience, but...what exactly did that do here?

 

[NHmaster]

There seems to be some confusion on the condensing issue. The Buderus gb series, the Baxi's and the Viessmanns are all condensing boilers. When the boiler is fired, reqardless of modulated input, the boiler condenses.

So what's the difference in AFUE? between that and a non condensing boiler, say the Weil McLain GV series? 95 afue vs 84 afue and a little more than a grand in cost. so for the extra thou you pick up about 11% afue. You also pick up some additional install costs. Is it worth the extra? Your call. For my money probably not. Though I like Buderus products I think the cast iron weil mclain gives you more bang for the buck in terms of service and longevity.

 

[GrumpyPlumber]

I recall my first conversation with the "boiler man" at the supply when I asked how the boiler could still condense at 180.
He made the point very simple with the 210/steam reverse effect.

Though you get less condensation at higher temps (and lower efficiency), it still condenses.