Analysis of my new Buderus boiler - seeking advice/feedback

DrewS

Hi All! First time poster here. I wanted to detail the experience I’ve had with my newly installed oil boiler, and get some of your expert insight on how I can optimize my system for further fuel efficiency. We moved away from a home that had gas heat, so I’m completely green when it comes to oil heating systems and could use a little advice.

To give you a bit of background, we recently moved into our new home last summer, in a town an hour southwest of Boston. The house has about ~2,500 sqft of living space. The previous boiler was a 35 year old Burnham V-14A, gross output 124,000 btu and net 107,000 btu. We have 4 zones (1 large zone, and 3 smaller zones). Our DHW is produced by a separate oil fired boiler (brand is Thermo-Flow, 30 gal, w/ a Beckett burner). Our oil tank is 330 gallons. Length of existing SlantFin baseboard is 163 feet. House is generally well insulated and air sealed (2x6 framing), but most of the windows are shot and are very drafty (looking to replace these soon).

When we bought the house, we knew more or less that the system was fully depreciated and on its last leg. Unfortunately for us, it was actually on its death bed. We found out early into this winter season that the heat exchanger was cracked and rotted out, and leaking out of the bottom of the system onto the basement floor (our home inspector did not catch it...rats!). Being that we were in a semi-heating emergency situation, we scrambled to pull together some quotes and get a replacement in ASAP before complete failure. As a result of not having the luxury of time to do a full heat loss analysis, I’m stuck with what I believe to be an oversized system (more on that in a bit). We ended up replacing the system with a Buderus G115ws/5 with a Logamatic R2107 control with outdoor reset. This system has a gross output of 136,000 btu and net 119,000 btu. So far everything has been working well. The burner is a Carlin EZ-1HP [based on spec sheet: firing at 1.16gph, head setting .75, pump pressure 185]. The system has 5-zone Taco ZVC405-4 relay, and a Grundfos Alpha 15-55F/LC variable speed circulator. We opted to not put in an in-direct DHW tank at the time due to budget constraints. Although we did have them install a stub out for a future indirect whenever the current tank decides to go.

I’ve done a lot of tweaking to the Logamatic settings to dial it in to the point that it barely keeps up with the heat load of our largest zone. Our installer wasn’t that knowledgeable with the Logamatic control, so it was ultimately up to me to figure that out (Buderus apparently does not provide over the phone technical support). These are the settings I’m am currently working with:

• Ref Temp: 168°
• Offset: +2°
• Heating Curves: 120° @ 50°, 149° @ 32°, 178° & 14°

So, we just had our first tank fill up today since the system was installed. Over 59 days, we went through 250.7 gallons of oil. Given that the burner operates on 1.16g/hr that puts us at around an average of 3.66 hours of burn a day using rough arithmetic. Are we getting good gas mileage on this thing or are we burning through way more oil than necessary? Is that hard to quantify if we have a separate appliance that also utilizes oil for DWH? Side note – The Logamatic still shows 0 for “Hours Run.” Any thoughts on why that meter is not working? Could it have been wired incorrectly?

Now – let’s talk boiler sizing. As it stands, I’m certain we have an oversized system and I’m sure y’all will concur. Having said that, we are planning to finish our attic in the next few years, which will add an additional 600 sqft to the load. Also, we plan on adding an indirect DHW tank down the road too. Will these additions add enough volume to system to offset the current oversized conditions? Is there a way to safely tweak the settings of the burner to downfire and generate longer burn times to curb short cycling? I’m interested to hear from you all now that I have given you the lay of the land.

General observation: Why is it that all of the HVAC pros we had come out to give us a quote recommended boilers around the same size as the one we had? Is it just pure laziness on their part to not do their due diligence with a thorough heat loss analysis to properly size the thing? Thanks in advance and apologies for the long winded post!

SuperTech

Downfiring is a possible option, but we would have to know some very important information. The combustion analysis numbers after start up. I hope you had your installer do that.

Most important thing to do to conserve oil is making sure that the home is sealed up well. Good insulation and windows are more important than anything you can do with tweaking the performance of the boiler.

I do think that an indirect tank would be more efficient than the direct fired water heater. Make sure they install a mixing valve on it.

Jellis

Yes sadly many contractors who replace boilers just look at the size of the existing boiler and if there are no obvious sizing complaints they replace it with a similar size.
I've encountered many reasons for this, it basically boils down to guys not taking enough time to do a heat loss calc and not wanting to be on the hook if they put in too small a unit.

DrewS

SuperTech said:

Downfiring is a possible option, but we would have to know some very important information. The combustion analysis numbers after start up. I hope you had your installer do that.



Most important thing to do to conserve oil is making sure that the home is sealed up well. Good insulation and windows are more important than anything you can do with tweaking the performance of the boiler.



I do think that an indirect tank would be more efficient than the direct fired water heater. Make sure they install a mixing valve on it.

RE: Combustion analysis: I'll have to comb through the paperwork packet I have from the contractor. If I can't find these details, can the Logamatic run these numbers? What metrics should I be honing in on? Thanks!

DrewS

Jellis said:

Yes sadly many contractors who replace boilers just look at the size of the existing boiler and if there are no obvious sizing complaints they replace it with a similar size.
I've encountered many reasons for this, it basically boils down to guys not taking enough time to do a heat loss calc and not wanting to be on the hook if they put in too small a unit.

Thank you. That was my gut instinct too. It all boils down to avoiding liability at the end of the day. I'm hoping that adding in the Logamatic and increasing the load via a new zone and in-direct DHW tank will help mitigate the negative impact of an oversized system.

Jamie Hall

On the windows. Be rather cautious on those. If they are good, original double hung windows, you will be much better off by having a good carpenter (or yourself, if you are handy and like carpentry) check their fit and adjustment, and then installing very good storm windows (I use windows by Innerglass --- www.stormwindows.com -- in restoration work, but you can also get high quality triple track windows if you need screens). Unless you get top of the line replacement windows, you will not get what you are looking for.

DrewS

Jamie Hall said:

On the windows. Be rather cautious on those. If they are good, original double hung windows, you will be much better off by having a good carpenter (or yourself, if you are handy and like carpentry) check their fit and adjustment, and then installing very good storm windows (I use windows by Innerglass --- www.stormwindows.com -- in restoration work, but you can also get high quality triple track windows if you need screens). Unless you get top of the line replacement windows, you will not get what you are looking for.

Thank you for the suggestion. They are all wood double-hung windows and are in rough shape. Most of them have cracking/broken/leaky jamb liners and sashes that are out of alignment or rotting. I can't lock the sashes on a good handful of them. We have been getting quotes on window replacements, and I have to say, are absolutely stunned by the prices we have been getting for wood aluminum clad replacements. I've been looking into sash replacement kits as well but I've heard if you're existing framing is not perfectly square that you'll run into performance issues.

EBEBRATT-Ed

@DrewS
" General observation: Why is it that all of the HVAC pros we had come out to give us a quote recommended boilers around the same size as the one we had? Is it just pure laziness on their part to not do their due diligence with a thorough heat loss analysis to properly size the thing? Thanks in advance and apologies for the long winded post!"

Yes it's oversized.

Most contractors don't want to do a heat loss without a commitment.

Here's the problem.

How long does it take to do a heat loss? Probably a good hour to measure up the house and poke around. This is in addition to looking at the old boiler and making a material list and figuring out any installation difficulties so they can estimate the job. So lets say at the job site for 2 hours + travel

Then to go back to his office, estimate the job, type up a proposal plug the heat loss estimate into a program come up with the answer select equipment etc etc.

So lets say 1 1/2 hours at the office.

Now he has 3 1/2 hours (pretty much half his day) into a job he may not get

Hi compitetion come to the house spends 20 min getting the size of the old boiler and looking around.

Goes back to his office and estimates, selects equipment and types a proposal in 3/4 of an hour so he has a little over an hour in it.

Then most (but not all) homeowners take the cheapest price.

Who gets the job?, Who gets most jobs?


Is it right? No but that's the way it is

HVACNUT

In the 2107, on the green terminal block (Brenner) , terminal 8 must jump to either 10 or 11, whichever is the load side powering the burner. That's the burner run time counter.
If a zone isn't what you think it should be then whip out the I&O and User manual's. There are a lot of parameters to go through. Too many to list here.
If you need manual's, I can upload them.

DrewS

HVACNUT said:

In the 2107, on the green terminal block (Brenner) , terminal 8 must jump to either 10 or 11, whichever is the load side powering the burner. That's the burner run time counter.

If a zone isn't what you think it should be then whip out the I&O and User manual's. There are a lot of parameters to go through. Too many to list here.

If you need manual's, I can upload them.

Thanks I'll take a look at that when I get home to see if it's wired correctly.

DrewS

EBEBRATT-Ed said:

@DrewS
" General observation: Why is it that all of the HVAC pros we had come out to give us a quote recommended boilers around the same size as the one we had? Is it just pure laziness on their part to not do their due diligence with a thorough heat loss analysis to properly size the thing? Thanks in advance and apologies for the long winded post!"

Yes it's oversized.

Most contractors don't want to do a heat loss without a commitment.

Here's the problem.

How long does it take to do a heat loss? Probably a good hour to measure up the house and poke around. This is in addition to looking at the old boiler and making a material list and figuring out any installation difficulties so they can estimate the job. So lets say at the job site for 2 hours + travel

Then to go back to his office, estimate the job, type up a proposal plug the heat loss estimate into a program come up with the answer select equipment etc etc.

So lets say 1 1/2 hours at the office.

Now he has 3 1/2 hours (pretty much half his day) into a job he may not get

Hi compitetion come to the house spends 20 min getting the size of the old boiler and looking around.

Goes back to his office and estimates, selects equipment and types a proposal in 3/4 of an hour so he has a little over an hour in it.

Then most (but not all) homeowners take the cheapest price.

Who gets the job?, Who gets most jobs?


Is it right? No but that's the way it is

Makes total sense from a time = money perspective. I also feel if I had done my own analysis, they'd reject it anyways as they wouldn't want to take on the onus of any fallout if mine was off/wrong. Ultimately, it sounds like I'm really at the mercy of the industry and that technicians who offer to do a heat loss analysis during the consultation are few and far between.

Either way, I'm stuck with the equipment I have now. How can I turn these lemons into lemonade? haha

Jamie Hall

Back to windows. Yes indeed. Good quality replacement windows are very expensive -- and in windows, you tend to get what you pay for. Lower grade windows will disappoint you -- badly.

It does sound as though your existing windows are in pretty tough shape, though. That said, however, unless the rough framing of the window (not the trim/parting strips/jambs etc.) is also damaged, a good carpenter can repair them. He or she can also repair the sashes (or if the rot is bad, even rebuild them). Perhaps I am a little overzealous on this -- but honestly, I and my carpenters have done a lot of windows, dating from 1750 to 1950, and we have yet to hit one which couldn't be repaired -- for less than a quality replacement window (I might add that if the have old glass -- prior to about 1900 -- they can't be replaced for any price and must be repaired... very carefully!, but that's another story).

STEVEusaPA

Why would you feel the boiler is oversized if it's barely keeping up with one (largest) zone?
Combining zones and TRV's might be the solution. Another option would be a buffer tank if it is in fact oversized.
Tightening up the house is necessary but would make it worse if the burner is short cycling.
As far as Heat Loss for oil fired equipment, I usually do a quick loss from my little app I made based on consumption.
Smaller houses, medium sized house with good insulation are always oversized for the smallest boiler.
Many of the oil-fired boilers come with multiple firing rates that will cover the range, and are the same price, so if necessary I'll price the larger boiler, which is usually not much different. After contract signed, I'll do a full heat loss.

DrewS

STEVEusaPA said:

Why would you feel the boiler is oversized if it's barely keeping up with one (largest) zone?
Combining zones and TRV's might be the solution. Another option would be a buffer tank if it is in fact oversized.
Tightening up the house is necessary but would make it worse if the burner is short cycling.
As far as Heat Loss for oil fired equipment, I usually do a quick loss from my little app I made based on consumption.
Smaller houses, medium sized house with good insulation are always oversized for the smallest boiler.
Many of the oil-fired boilers come with multiple firing rates that will cover the range, and are the same price, so if necessary I'll price the larger boiler, which is usually not much different. After contract signed, I'll do a full heat loss.

Thank you for the response. I feel it's oversized based on the average burn time (~3.5 - 8 minutes depending on the weather). The system is barely keeping up with the largest zone because I have, I think, effectively dialed in my outdoor reset and Logamatic control. Would the fact that I'll be adding an indirect DHW tank and another 600sqft heating zone make a big difference in burn performance?

STEVEusaPA

Ah, I see now.
Your additional load to the boiler may not help much. The DHW will run about 10 minutes to recharge, and another 600 sq feet on it's own zone will short cycle. Unless you switch your indirect to a reverse indirect and run all the zones off it, mixed down.
Then your boiler is basically recharging the tank only.
The downside is now your keeping all that water hot year round.
That's why I recommended combining zones and a separate buffer tank, so when your in WWSD, you're not keeping all that water hot.

DrewS

STEVEusaPA said:

Ah, I see now.
Your additional load to the boiler may not help much. The DHW will run about 10 minutes to recharge, and another 600 sq feet on it's own zone will short cycle. Unless you switch your indirect to a reverse indirect and run all the zones off it, mixed down.
Then your boiler is basically recharging the tank only.
The downside is now your keeping all that water hot year round.
That's why I recommended combining zones and a separate buffer tank, so when your in WWSD, you're not keeping all that water hot.

Thanks again! Maybe the ideal move then would be to tie the new living area to an existing zone. It would also require less intensive plumbing as I'd be connecting my piping from a nearby room instead of all the way from 3rd floor to basement through every wall. How much does a buffer tank cost roughly, and how big is it?

STEVEusaPA

Pricing is not allowed per site rules.
Size depends on which size you need, depending on wanting about a 10 minute run time on the smallest zone. The basically are the same footprint as a water heater.
Here's a wealth of free information to help you.
https://www.caleffi.com/usa/en-us/technical-magazine
I recommend this one specifically:
https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_17_na.pdf

BDR529

Logomatic, control heat curve yadda yadda yadda...

I've had them fail and the client didn't have the $$ to replace. So we ran it in manual with a relay for the domestic.

2 year review, little to no change of fuel consumption.

Ironman

163’ of BB is good for about 80k btus @170* AWT. 136k btu output, you’re almost twice the size you should be.

Unfortunately, you can NOT down fire a Buderus. Don’t let anyone try.

Combing as many zones as possible + a buffer tank and TRVs as Steve mentioned may be your best solution.

DrewS

> @Ironman said:
> 163’ of BB is good for about 80k btus @170* AWT. 136k btu output, you’re almost twice the size you should be.
>
> Unfortunately, you can NOT down fire a Buderus. Don’t let anyone try.
>
> Combing as many zones as possible + a buffer tank and TRVs as Steve mentioned may be your best solution.

When I add the 3rd floor I estimate that'll give me about another 25k btus of baseboard. Better but still not great. Regarding zones: Right now the house has two zones on the first floor. One big one consisting of the kitchen, living room, dining room, and foyer. The other is a much smaller zone for a den and in-law apartment. Second floor has two smaller zones. One for the master bedroom and one for the other two bedrooms. If I were to add conditioned space in my attic, what would be the most ideal zone configuration? Tie the first floor zones as one, and the second and third floors as one ?

I'm unfamiliar with TRVs. Do they need to be installed on every baseboard of just one per zone? My circulator does modulate the pump speed depending on how many zones are calling for heat for what it's worth.

Can you elaborate more on why downfiring a Buderus is a big no-no?

Thanks for the feedback!

Ironman

The Buderus block is already oversized compared to others. Down-firing can cause combustion issues as well as flue gas condensation. It can be up-fired 10%, but not down-fired.

Ironman

TRV = Thermostatic Radiator Valve. The placement of them would depend on the layout of your house and how the radiators are piped.

DrewS

> @HVACNUT said:
> In the 2107, on the green terminal block (Brenner) , terminal 8 must jump to either 10 or 11, whichever is the load side powering the burner. That's the burner run time counter.
> If a zone isn't what you think it should be then whip out the I&O and User manual's. There are a lot of parameters to go through. Too many to list here.
> If you need manual's, I can upload them.

Here's the current wiring, which looks identical to the diagram in the manual. So you're saying then jump 8 to 11 in this case?

HVACNUT

Yes. Terminal #11 should be 120v power to the burner. So put a jumper between #11 and #8.

DrewS

HVACNUT said:

Yes. Terminal #11 should be 120v power to the burner. So put a jumper between #11 and #8.

Thank you again. That did the trick!

HVACNUT

> @DrewS said:
> (Quote)
> Thank you again. That did the trick!

Happy to help. Now get to reading those manuals.
With a .85 nozzle at 185 psi, its firing 1.15 GPH input. That's a lot. You probably would've been fine with a 3 section. Read the material and tweak what you can.

DrewS

HVACNUT said:

> @DrewS said:

> (Quote)

> Thank you again. That did the trick!



Happy to help. Now get to reading those manuals.

With a .85 nozzle at 185 psi, its firing 1.15 GPH input. That's a lot. You probably would've been fine with a 3 section. Read the material and tweak what you can.

I agreed that it seems excessive. But as Ironman mentioned above, Buderus doesn't respond well to downfiring inherent to its design. Do you concur with that?

Pardon by ignorance, can you explain what a 3 section is? I've read through the manuals a few times to adjust the Logamatic. What section are you referring to as far as firing rates go?

Thanks!

HVACNUT

> @DrewS said:
> (Quote)
> I agreed that it seems excessive. But as Ironman mentioned above, Buderus doesn't respond well to downfiring inherent to its design. Do you concur with that?
>
> Pardon by ignorance, can you explain what a 3 section is? I've read through the manuals a few times to adjust the Logamatic. What section are you referring to as far as firing rates go?
>
> Thanks!

I wasn't suggesting you downfire it, just stating what the firing rate is. The boiler is currently firing at 1.15 GPH, or roughly 154K BTU input. A heat loss calculation would have been terrific.

You have the G115/5. 5 cast iron sections. The G115/3 probably would've been more than enough.

Can you post the specs that states a 1.15 GHP firing rate using the Carlin EZ 1 with the G115/5.
My lit may be old but it says 1.00 GPH max on a G115. Next you move up to the G215 that starts at 1.10 GPH.

gerrytheoilman

Get a heat loss on your house first. If your not keeping up in your room you may not have enough baseboard in the room for design temp set logamatic to service mode let it run high limit see if it heats fine. It does sound grossly oversized Ive seen a g115 4 section heat a mansion with hot water priority and Modine heaters in garage. It all comes down to the heat loss and the output of baseboard available. Pretty sad they didn't install a indirect to keep boiler running nice all year I would suspect a decent consumption from your oil fired water heater too, seems like a goofy setup not to bash the installer but they have high output indirects that have great recovery and literally are built for this system setup.

DrewS

HVACNUT said:

> @DrewS said:

> (Quote)

> I agreed that it seems excessive. But as Ironman mentioned above, Buderus doesn't respond well to downfiring inherent to its design. Do you concur with that?

>

> Pardon by ignorance, can you explain what a 3 section is? I've read through the manuals a few times to adjust the Logamatic. What section are you referring to as far as firing rates go?

>

> Thanks!



I wasn't suggesting you downfire it, just stating what the firing rate is. The boiler is currently firing at 1.15 GPH, or roughly 154K BTU input. A heat loss calculation would have been terrific.



You have the G115/5. 5 cast iron sections. The G115/3 probably would've been more than enough.



Can you post the specs that states a 1.15 GHP firing rate using the Carlin EZ 1 with the G115/5.

My lit may be old but it says 1.00 GPH max on a G115. Next you move up to the G215 that starts at 1.10 GPH.

Thanks I'll have to double check the spec on that again later today. It's possible I grabbed the G215 # instead of G115.

DrewS

gerrytheoilman said:

Get a heat loss on your house first. If your not keeping up in your room you may not have enough baseboard in the room for design temp set logamatic to service mode let it run high limit see if it heats fine. It does sound grossly oversized Ive seen a g115 4 section heat a mansion with hot water priority and Modine heaters in garage. It all comes down to the heat loss and the output of baseboard available. Pretty sad they didn't install a indirect to keep boiler running nice all year I would suspect a decent consumption from your oil fired water heater too, seems like a goofy setup not to bash the installer but they have high output indirects that have great recovery and literally are built for this system setup.

In their defense they did suggest a new indirect, but due to my own budget constraints I wasn't able to drop another few grand when I barely had the funds available to replace the boiler itself. I figure when I renovate my attic in a couple years will be the perfect opportunity to A) Run new baseboard and link up some of the micro-zones, Add an indirect, and C) Add a buffer tank to add more volume to the system and reduce short cycling.

DrewS

HVACNUT said:

> @DrewS said:

> (Quote)

> I agreed that it seems excessive. But as Ironman mentioned above, Buderus doesn't respond well to downfiring inherent to its design. Do you concur with that?

>

> Pardon by ignorance, can you explain what a 3 section is? I've read through the manuals a few times to adjust the Logamatic. What section are you referring to as far as firing rates go?

>

> Thanks!



I wasn't suggesting you downfire it, just stating what the firing rate is. The boiler is currently firing at 1.15 GPH, or roughly 154K BTU input. A heat loss calculation would have been terrific.



You have the G115/5. 5 cast iron sections. The G115/3 probably would've been more than enough.



Can you post the specs that states a 1.15 GHP firing rate using the Carlin EZ 1 with the G115/5.

My lit may be old but it says 1.00 GPH max on a G115. Next you move up to the G215 that starts at 1.10 GPH.

I found the Carlin burner spec sheet and compared it to the Buderus literature. Now I'm even more confused by the differing configuration. Buderus states that the firing rate should be 1.00gph, whereas Carlin lists the rate at 1.16gph, which is what my burner seems to be set up for at the moment. The sticker on the boiler also states that the max firing rate is 1.10gpf. Is there a good reason for this variance, or would it make sense to reach out to Carlin?

mattmia2

I'd go with the ratings plate. In the decades between when the manual was written and your unit was manufactured, what was actually being produced may have changed.