Burnham Alpine 150 ModCon likely oversized and not working at highest efficiency

[annelisemcl]

Let's start with me as the homeowner admitting I did everything wrong on this install 7 years ago. Back story: in 2010 bought a slab ranch house in SE PA (think suburb between Philly & Wilmington De) 3 bedroom, 2 bath at about 2100 sqft with cast iron baseboard heat all on 1 zone with separate electric DHW. Had an HVAC guy remove the old oil boiler to replace for a propane system (no gas line on the street & transferring my gas stove to this new to my family house). Without any heat loss calculation, the HVAC installer put in the Alpine 150 System (evidently oversized per reading threads here) AND he did not install the outside sensor AND I have been using a honeywell thermostat setting back about 5 degrees at night (60 degrees) verses the day when occupied temp of 65 degrees. I had the boiler serviced last year (delayed so long due to me not making it a priority and having a hard time getting any local techs who will work on Propane & the Alpine unit). (We converted the attached garage to a bedroom with a split system recommended by Dana & a bathroom with a ceiling radiant heater on thermostat aslo recommended by Dana here - thanks!)

I am obviously not utilizing this condensing efficient boiler to the max of its efficiency. I have a local tech who is listed on the US Boiler site scheduled to call to make an appointment with me to address a hard lockout code #27 (ignition failure) that I have been resetting. After reading some threads, these are my questions:

1. Should I get the outside temp sensor installed?
2. My set-back temp is & has been set to 187 degree (thus not running in the "max efficiency zone" near 120 degrees) and probably only cycles on 2-3 times a day total. I think pretty much the original installer left it at "factory settings". What would you recommend I ask the tech to test before setting the system to the most efficient use of this condensing boiler?
3. Currently there are hot & cold zones in my home due to previous owners removing or never tying in radiators AND we have a wood burning high efficiency soapstone stove that pretty much heats (and sometimes over heats our kitchen) and into our living room while the bedrooms are cooler (not necessarily a bad thing). What should I ask this tech as ideas to regulate/ balance out the heat?
4. Is there any hope for me to utilize the efficiency of this condensing boiler since it is so oversized?
5. Should my cast iron radiators never really get cold? If I let them cool down and then the system has to heat up to the 187 set-point (past efficiency) am I actually wearing the boiler down faster than multi-day short runs?

I am not DIYing this at all. This is way beyond my comprehension. Although late to the game, I want to work with a technician to get the most out of my boiler and to assure it lasts as long as possible while keeping my family and home comfortable. Please help and thanks in advance.
Ann Elise

 

[Dana]

Measure up the zone radiation on each zone, and list them. At minimum fire in condensing mode the ALP150 puts out about 28,500 BTU/hr (more than 3/4 of the heat load at my house at 0F), and if the zone radiation on each zone can't emit that much at condensing temps (boiler output of ~130F or lower) , it will cycle on and off during a call for heat from any one zone, how much it cycles matters. It's concievble that you don't have sufficient radiation in the whole house to deliver the 28.5K at condensing tempertures without cycling, but if there is enough thermal mass in the water it may not matter.

The napkin math on figuring it out lives here.

 

[Sponsor]

 

[annelisemcl]

Dana,
Thank you for replying. I was secretly hoping you would. I spoke with the local tech and I feel a bit better knowing he has a buderus modcon in his home and said we can definitely work to tweak our Alpine to attempt to get it into the max efficiency range if possible.

Now to the task you assigned me. I read your article (thanks). Honestly, much of it was over my head and brought to light how much I don't know because I don't have a heat loss calculation for my home nor a fuel use load analysis (our propane tank also is for cooking and clothes dryer). Some of the article information I do not understand. But here goes, my system is an existing 1950s closed loop 1 zone system. I measured and totaled ALL the cast iron baseboards in our home for a total of 155 feet. Here is where I start to get lost. You said the Alpine150 puts out 28,500 btu per hour in condensing range BUT I don't know how to calculate the needed btu's for my home to be comfortable because cast iron btus change based on the water temp flowing through the system. How do I calculate my homes needed btus? I don't understand how you determine the houses seasonal heat load. I know my "crappy" crystal replacement windows have a ufactor 0f 0.49 and I have been attempting to rudimentarily calculate a heat load based on the outside design temp of 13 degrees versus an indoor design temp of 70 degrees with a delta t of 57. But after this my eyes start to cross.

I'll keep plugging to get the numbers but I would appreciate any hints or tricks to get them figured out faster. (Just assume every post is ending with thank you, much thanks, thanks so much...)

 

[Mage182]

I have this boiler (although probably an older version of Sage than you have), and my house is smaller in square footage. I have cast iron baseboard throughout the house and DHW tank piped as a zone. I'll just make a list of notes.

• I don't have the DHW configured as priority. Everything can run at once if needed. Your DHW is separate so that probably doesn't matter.
• I set my high limits close to the minimum so the max fan RPM is low. This helps control cycling.
• I set my under/over setpoint temps to have a pretty wide range. I find that if some calls do bump off the max temp, the calls for heat end before the temp makes it back down to the minimum under and the boiler cycles again.
• Outdoor reset is set up. The system struggles the most when it's warm out. I'm installing a ductless system in the whole house to take care of heating during the 'shoulder' times of year.

Do you have the new Burnham zone control box? What I've read about it looks good and it makes the system as a whole smarter. My version of Sage doesn't support it, but if yours does it might be worth looking into.

If you're handy a lot of the sensors that go bad on these units (ignitors, water and flue temp sensors, etc) are easy to diagnose and the parts are relatively cheap on sites like SupplyHouse. I keep a small box of spare parts just in case.

 

[Dana]

Dana,
Thank you for replying. I was secretly hoping you would. I spoke with the local tech and I feel a bit better knowing he has a buderus modcon in his home and said we can definitely work to tweak our Alpine to attempt to get it into the max efficiency range if possible.

Now to the task you assigned me. I read your article (thanks). Honestly, much of it was over my head and brought to light how much I don't know because I don't have a heat loss calculation for my home nor a fuel use load analysis (our propane tank also is for cooking and clothes dryer). Some of the article information I do not understand. But here goes, my system is an existing 1950s closed loop 1 zone system. I measured and totaled ALL the cast iron baseboards in our home for a total of 155 feet. Here is where I start to get lost. You said the Alpine150 puts out 28,500 btu per hour in condensing range BUT I don't know how to calculate the needed btu's for my home to be comfortable because cast iron btus change based on the water temp flowing through the system. How do I calculate my homes needed btus? I don't understand how you determine the houses seasonal heat load. I know my "crappy" crystal replacement windows have a ufactor 0f 0.49 and I have been attempting to rudimentarily calculate a heat load based on the outside design temp of 13 degrees versus an indoor design temp of 70 degrees with a delta t of 57. But after this my eyes start to cross.

I'll keep plugging to get the numbers but I would appreciate any hints or tricks to get them figured out faster. (Just assume every post is ending with thank you, much thanks, thanks so much...)

To be clear, I'm assuming that is 155 square feet EDR (equivalent direct radiation, using the methods found here), rather than linear feet of diverse types of radiation or something else.

Assuming 155' EDR, at minimum modulation of 28,500 BTU/hr that becomes a ratio of 184 BTU/hr per square foot EDR. If you look at the nomograph on p.2 of that radiator sizing document you'll see that the radiators will emit that much only at an average water temperature of about 180F (which usually means a boiler output temperature of 190F, a return water temperature of 170F). If the boiler is set below that temperature there is more heat going into the radiators than is being emitted, which causes the boiler to cycle on/off.

To actually run at a bare 88-90% condensing efficiency the return water temperature needs to be about 125F, which happens when the boiler is putting out ~135F water, with an average water temperature of about 130F. Looking at that same nomograph at an AWT of 130F the radiators are emitting about 70BTU/hr per square foot EDR. So with 155' of rad you're looking at 70 x 155= 10,850 BTU/hr of heat being delivered to the house, but the boiler is putting about 28,500 BTU/hr into the system (at minimum fire). With 28,500 - 10,850= 17,650 BTU/hr of excess heat going into the water, the temperature rises, the boiler senses that it's temperature output is going higher than the set point (whether outdoor reset setpoint, or programmed fixed temperature), and it turns the burner off, then turns it back on after enough heat has been emitted by the radiators to cool the water back into range. So under those conditions during an extended call for heat from the thermostat the burner will cycle on/off, operating at a 10,850/28,500 (= 38%) duty cycle.

As long as there is enough water + iron thermal mass in those radiators and pipes to keep the burn times to at least ~3 minutes and off times of ~5 minutes (3/(3+5)= ~38%), there will be 7-8 burns per hour, which isn't great, but it's not terrible. When it's 10+ burns/hour and 2 minute burn times it's taking a toll on efficiency, and putting excessive wear & tear on the boiler.

So, to decide whether it's worth adding the outdoor reset sensor and programming the boiler to ramp the temperatures up or down as the outdoor temperature changes (aka "outdoor reset"), you need to do some experimenting. Program the output temperature to 125F, turn up the thermostat to 80F or something to ensure that it takes a long time for the house to come up to temperature. Then, using a stopwatch or a watch with a second hand, time the first 4-5 burn cycles, and off cycles, measured to the nearest 10 seconds. If it's looking like it'll be fewer than 10 total cycles per hour with the average burn time being 3 minutes or more it'll definitely be worth setting it up for outdoor reset.

Whether or not 155' EDR of radiator is enough to keep you warm at +13F even at the maximum output temperature of the boiler can be determined by fuel use. The error from other uses of propane such as hot water or cooking/laundry etc is offset by the error introduced by solar gain coming in your windows during daylight hours, and the overall magnitude of fuel use is small compared to what is used for heating during the winter months. So logging the exact fill-up dates and quantities, then downloading heating degree-day data from a nearby weather station (use base 65F data, which is the long standing standard for a 70F home) using 5th grade arithmetic you can calculate the gallons used per heating degree-day, then divide by 20 hours/day to come up with gallons per heating degree-hour. For purposes of illustration, let's assume that comes out to 0.0065 gallons per degree-hour.

Every gallon of propane has 91,600 BTU of source fuel energy. Assuming it was operating near the condensing zone most of the time, use 90% for the approximate efficiency, so out of each gallon you end up with 0.95 x 91,600 = ~87,000 BTU of heat going into house per gallon of fuel burned. So with 0.0065 gallons per degree-hour, that becomes 87,000 x 0.0065= 566 BTU per degree hour.

The presumptive heating/cooling balance point when using base 65F data is that there is zero heat needed when it's 65F outside. With a heating constant of 566 BTU per degree-hour, for every degree F below 65F would require putting that much heat into the house to keep it warm. If the the outside design temperature is 13F, that means you have 65F-13F= 52F heating degrees (not the 57F delta-T you would use for Manual-J or IBR type heat load calculations), and a design heat load of about 52F x 566BTU/F-hr= 29,432 BTU/hr.

With 155' EDR of radiator and a load of 29,492, which is a ratio of 29,492/155= 190 BTU per square foot EDR. If you refer to the nomograph in that radiator sizing document you'll see that you need an average water temp of about 195F for the radiators to emit that much. That would require an output temperature of about 205-210F, which is probably above the maximum operating temperature of the ALP150, so if it happens that those are the numbers, you'll either need more radiator, a different boiler, or fix up the house to lower the space heating load.

Assuming the walls and attic are already insulated, and all window are at least U0.6 or lower (a wood sashed single pane with a clear glass storm window is ~U0.5), blower door directed air sealing and insulating the foundation (in that order) are two of the biggest and most cost effective ways of reducing the space heating load.

 

[annelisemcl]

To be clear, I'm assuming that is 155 square feet EDR (equivalent direct radiation, using the methods found here), rather than linear feet of diverse types of radiation or something else.

SO, don't assume So, yeah the 155 was the total linear feet. I just googled search for my 9 inch tall cast iron baseboard and each linear foot is an equivalent 3.4 EDR so multiplying 155 x 3.4 gives me 527 sf EDR.

So plugging the correct number into your math gives me a 56 btu per sqft EDR giving me a water temp of 120-130 degrees (right in the sweet spot, correct?)

The local tech is coming tomorrow, so I'll see what comes of that.

 

[annelisemcl]

I have this boiler (although probably an older version of Sage than you have), and my house is smaller in square footage. I have cast iron baseboard throughout the house and DHW tank piped as a zone. I'll just make a list of notes.

• I don't have the DHW configured as priority. Everything can run at once if needed. Your DHW is separate so that probably doesn't matter.
• I set my high limits close to the minimum so the max fan RPM is low. This helps control cycling.
• I set my under/over setpoint temps to have a pretty wide range. I find that if some calls do bump off the max temp, the calls for heat end before the temp makes it back down to the minimum under and the boiler cycles again.
• Outdoor reset is set up. The system struggles the most when it's warm out. I'm installing a ductless system in the whole house to take care of heating during the 'shoulder' times of year.

Do you have the new Burnham zone control box? What I've read about it looks good and it makes the system as a whole smarter. My version of Sage doesn't support it, but if yours does it might be worth looking into.

If you're handy a lot of the sensors that go bad on these units (ignitors, water and flue temp sensors, etc) are easy to diagnose and the parts are relatively cheap on sites like SupplyHouse. I keep a small box of spare parts just in case.

Thanks so much, Mage182! I am handy when I am able to watch a pro video or live technician so I know what to do in the future. I appreciate all your suggestions. If my math is correct per Dana's response (but who knows because my garbage mistake equates to "garbage in, garbage out") it seems I may be in the perfect sweet spot to utilize this modcon boiler to its best efficiency. I am just frustrated with myself that it took me 7 years to really focus to get this operating correctly. And we do keep our home on the cooler side at an average of 65 degrees.

I will look into the Brunham zone control box (thanks!). Right now I have been getting a fault 27 (ignition failure) but I don't know if the ignitor is going bad or there is something else wrong.

 

[Dana]

The 9" cast iron is usually good for ~200 - 230 BTU/hr per linear foot at an AWT of 120F (well into the condensing zone), so with 155 linear (x 200 BTU/hr) it will handle 31,000 BTU/hr from the boiler without cycling AT ALL. With the thermal mass of it's water volume + cast iron it should be able to run 110F water without excessive cycling.

So you should be able to set this up with outdoor reset and start dialing in the curve parameters for maximal efficiency & comfort without short-cycling it into an early grave. Whether it's too much boiler for the LOAD remains to be seen, but with your radiation being oversized for the load won't affect efficiency much.

 

[annelisemcl]

Thanks, Dana! The tech was here today to first address the boiler's fault code issue. The US boiler rep thought it might by the control board (of course 7yr old so 2 years out of warranty) BUT suggested changing the high temp sensor first as that is a cheaper fix than a new board. I suggested to my husband if it is the board, that we buy a new board and switch it out ourselves but he has concerns. I was under the impression that a board replacement is relatively easy as a plug & play switch out. Any thoughts?

 

[Dana]

Board swaps are usually pretty straightforward, but I've never dealt with that on this boiler. It's a matter of how much you trust the tech's competence & diagnostic judgement.

 

[annelisemcl]

So, in advance of the rep returning to fix the fault that is causing my boiler to need a manual re-set or installing an outdoor reset, I started adjusting the temperature down in an attempt to have it run more efficiently as a condensing modulating boiler. I first reset my thermostat to not have large variating set-backs, (morning temp 65, sleeping temp 63) then I set the boiler's max temp to 135f to see if it could make the house comfortable.

here are my concerns happening thus far:
1. Even if the house thermostat shows the set temp of 65f the boiler will start running. Why?
2. This morning at 7:30am I awoke to the thermostat showing 61f at a 65f set temp. The boiler needed a re-set. I re-set and it took till noon for the house thermostat to reach 65f (and that is with our wood stove running at above 300f by 10am on the opposite side of the house). This means the boiler was running for 5 hours to reach temp. Am I spending more money on electricity while less money on fuel? Doesn't that negate the fuel savings?
3. With the boiler at a max temp of 135f, part of the run is outside the "max efficiency" zone. Should I setback the max temp to 120f? Will that cause it to run longer? How can I determine if it is short cycling if I am hearing the circulating pump constantly running? Is short cycling only when the burner is ignited and flaming and not the circulating pump?

The more I try to understand and work with this boiler to get it in the highest efficiency zone, the more confused I get. Is this partially due to me working without an outdoor reset installed yet AND the boiler faulting and needing manual resetting or is this just way over my head?

Thanks for any response to help me get a more basic understanding of this system. (I will say that others in the home have said the house has had a more even temp throughout the day instead of our past warm & cold periods. Also, I think 63f is too warm at night sleeping because we all have complained of being "too warm" at night under our quilts but I fear a setback of 60f [our standard sleeping temp] will take a really long time for the boiler at 120f to reach the morning work and school leaving 65f temp).

Feeling frazzled and very dumb, Ann

 

[Dana]

Setting the temperature higher will reduce the recovery ramp times, setting it lower will increase those times. To get the best efficiency out of these things it's better to NOT use overnight setbacks, since that increases the firing rate necessary to achieve reasonable temperature recovery times. Some boilers have a programmable "boost" function that can raise the output temperature if the thermostat hasn't been satisfied within a (user-programmable) length of time to allow overnight setbacks without ridiculously long recovery times.

Make the manual your bedtime story for the next week or so- a lot of this stuff will become clear after absorbing it.

Electricity has to be SUPER expensive to exceed the fuel cost savings, but it is still an important secondary operating cost that should be considered in every design. Most systems are over-pumped, and most are using lower efficiency pumps. With the high duty-cycle of the system pumps on condensing systems it's well worth using ECM drive pumps and "smart" pumps to minimize pumping power use. A dozen years ago the expense of the higher efficiency pumps was high enough to make it questionable to use them in low electricity pricing markets, but at current high efficiciency pump prices it's become a no-brainer- just do it.

If you're having to manually bump the temps up and down it's impossible to get it totally right, and if the boiler is suffering logic-board problems it only makes it more confusing.

You can never really tell the state of the burner by the circulation pumps. It can be short cycling like crazy even when the pumps are running continuously. Most condensing boilers are capable of displaying the burner information on the front panel, many will also log the numbers of burns, etc.

 

[annelisemcl]

So, tech was here and replaced the igniter switch and flame sensor and the high limit kit and cleaned the boiler. An outdoor reset has not been installed yet. My boiler is still showing an ope fault for the "auto reset high limit contact" and he is getting pricing to replace the entire control board (around $600) BUT I am thinking of holding off to see if the lockout needing reset is fixed without replacing the board.

I have set the high limit setpoint to 130F with a 5F above limit and a 20F below limit restart.

I was able to calculate my average run time and it is 22.34 minutes. Is that good or bad? My max fan speed is set to the factory setting (about 5000rpm) with a minimum of 300rpm. Is it better for efficiency for me to reduce my fan speed to below the factory setting?

At this time my 2 Taco circulating pumps are not controllable. When the time comes for replacement, I will look into the more efficient pumps you suggested, Dana. (My tech has a buderus modcon that he designed the system with the flat european style wall panels and the ECM drive pumps. Fortunately this indicates to me even if he is not familiar with the Alpine specifically, he is familiar with the modcon concept).

Dana, I am reading the manual frequently hoping it will sink into my thick skull. As always, I so appreciate your help and replies. I may be late to the game but I am trying to utilize this to max efficiency. And even with all my concerns regarding this Alpine Modcon, I count myself lucky to have such helpful pros to guide me along this very difficult learning curve. Thank you, Ann

 

[NY_Rob]

22min runtime is acceptable especially since you're running on a set SWT (Supply Water Temperature) vs. an ODR curve based on an outdoor sensor. Most agree that a 6min runtime is the minimum acceptable to not be considered short-cycling.
The trick will be getting decent run times when it's 50F outside and your heatloss is only 5K BTU's for the whole house. You will need an ODR sensor for that!

Don't mess with the inducer fan speed, that's reserved for special/unique install situations.

Once you get ECM pumps, don't worry about electricity costs... my Grundfos Alpha pushes water through three open zones at just 14 watts. Even if it's running 18hrs/day that's only 6 cents/day in electricity even at $$$ NY electrical rates.

Check your boiler manual for a "step modulation" feature, it slowly ramps up the BTU output to full over time vs. full fire rate after ignition. It can lengthen run times, and reduce stress on your heat exchanger.

See if you have a "heating capacity" type setting where you can limit the total output of your boiler to a % of it's max BTU output. That can also increase burn time and reduce stress on your boiler. FWIW- I run my 80K BTU mod-con at 50% max fire rate and it's still plenty of BTU's to heat my house.

 

[annelisemcl]

Thanks, Rob for the reply and information. I'll look into those items you mentioned.

I also forgot to mention, that I am asking my propane supplier to give me my past years fuel usage so I can guesstimate the propane being used pre and post resetting my max temp set rate from 186f to 130f. I also have to keep in mind we supplement with wood at about $250-$500 per season depending on if I am splitting my own or getting seasoned delivered. So on those 50F days, I can also build a fire to keep most of the living areas warm (the bedrooms are cooler but that is what thick fuzzy quilts are for anyway!

 

[Dana]

F0r low mass mod-cons like the Alpine even a 3 minute burn time is acceptable, as long as it's only a handful of burns per hour. A 22 minute average burn time at 130F-out, operating at or near the minimum firing rate is awesome for efficiency!

The dollar amount doesn't tell me the heat content of the wood, or the efficiency of your wood burner, so it's hard to make the adjustments /corrections to the fuel-use heat load calculation. But unless the propane supplier can give you exact fill-up dates and amounts (as opposed to an annual total) it's not going to be very accurate anyway. The key to bear in mind as the weather cools of is whether the water temperature needs to be bumped up to stay comfortable.

Some of the temperature numbers I've been throwing out earlier are more accurate for a typical for natural gas boiler, not propane. The dew point temp of propane exhaust is a bit higher than that for natural gas (due to the higher ratio of H2O to CO2 in the exhaust product), so you won't lose much efficiency if you have to bump the boiler temp to 140F to stay comfortable, whereas raising the temp that high would take a substantial bite out of condensing efficiency with a natural gas burner.

 

[annelisemcl]

So last night it was 19F here and the only person who said they were cold was my teen daughter sleeping under a lightweight quilt (and she just pulled on another blanket). I did hear the boiler cycling on during the night, maybe 1x an hour but the house felt comfortable. We did have the wood stove burning overnight too but that warmth minimally reaches the bedrooms across the ranch home. (The whole house thermostat is in the farthest bedroom, mine)

I will keep the higher (140f) set-point in mind, Dana if this lower can't seem to keep up with the colder overnight temps going forward until I install an outdoor rest sensor.

I did get the propane fill dates and amounts but the numbers are ALL over the place and I don't know if it was annual average winter temps OR usage of our wood stove or both. So it is really just supposition at this point. But at least I have a comparison for 2018 with the lower set point to compare when it was set to 187f max for all those other years.

As always, thanks for all the help. Better windows and more attic space insulation will help to tighten up our heat loss too. (Previous owner put in Crystal Builder grade double hung windows & they are awful!)

Ann

 

[Dana]

If you take an entire winter's fill ups and estimate the number of cords of wood you went through in that period (and of what species) we could still make a crude estimate of the load. But if the thermostat was being satisified overnight with 130F water when it was under <20F increasing the boiler's setpoint isn't going to make your daughter any warmer. The thermostat is in a remote room, a room that may have different amount of heat coming in from the wood stove, and/or a different ratio of room radiation to room heat load.

With a bit of analysis of the exterior walls/ceiling/floor/windows of that room it might be possible to lower the heat load sufficiently in that room to warm it up a few degrees. Also, if your radiators have been painted a metallic silvery or gold color (as many antique radiators have been), the low-emissivity paint is reducing the heat output by 15-20%. Painting over the l0w-E paint in the colder rooms with just about any other paint (any color) will measurably improve the amount of heat being emitted, improving the room to room temperature balance. But ONLY re-paint the radiators in the colder rooms- if all of the radiators are re-painted the room-to-room temperature balance will remain about the same.