Ultimate Oil Boiler w/water leaking from below - considering replacement

historicalwork

I've been finding this forum a great resource for information on oil-fired boilers. We have a Ultimate Engineering (Model K-6T) (IBR ~160BTH). From what I could research, I believe the boiler is about 30 years old. We've been in the house only a few years. It feeds hot water baseboard throughout the old house. The unit vents to the chimney. We have an electric hot water heater (in decent shape). Last week the boiler started leaking water from around the base.

The service guys tell me it's something rusted or broken through underneath and the recommendation is for replacement. I also took the covers off around the boiler myself to make sure I didn't see any obvious signs of something leaking around a fitting. It just seems to come from underneath - the unit is barely raised off the concrete floor - so there is no water to look under. The water pressure seems ok and it's otherwise still operating. We have rags around the boiler and it seems like there probably a cup of water coming out a few times a day.

Part of me wonders if there is anything more to do. But, from what I read, trying any further repair is probably not of value given age, condition, etc. I guess - despite what I know isn't much for anyone to react to, would that be the general approach in this situation. Meaning, skipping any possible attempt to repair and consider a new boiler? So far, based on what I read and given the recommendation from the service guys, we are thinking of a Buderus G215/4. The heat loss calcs they did suggest about 140 BTU. Based on rough calcs using stuff on the internet, that seems in the ball park. They are also suggesting a Carlin burner? From quick searching, Riello is most often recommended but I didn't see anything negative about Carlin.

I recognize my question is a bit open ended. I'm just trying to double check my general thinking before committing to purchases. We are getting three quotes from what we believe are reputable companies. In any event, the information here on this forum is very much appreciated! To get a sense of the general condition, I attached a picture from inside the front panel. It's not pretty!

icesailor

Well, a bigger POS you couldn't find. Maybe a Repco or some other offloaded brand. The leak is probably at the tankless heater coil. It might be worth trying to replace the gasket but the bolts are all rusted in place, and it is a dry base boiler. With the seals gone. Do you have any scorching around the jacket at the level of that box the boiler is sitting on?

The best resolution to your problem is to disconnect the piping from the boiler, raise it up, and slide a new boiler under it.

Buderus's are nice. If you find that you need to squeeze the Eagle a little harder, there are other boilers that some consider a better value for the cash strapped.

You can have ANYTHING you want. Just not EVERYTHING.

You might want a BMW X-3 for your next kiddie car. But settle for a cheaper X-1. Or maybe a Subaru Outback. Or a Honda CR-V.

Choices.

Thanks for posting the photo so we can get a good idea of what you are facing.

johnshears

Had you changed the boiler or replaced it ? Well, I think it also need regular maintenance so that it cannot get corroded. It need regular cleaning also.

icesailor

Those dry based oil boilers like that one usually have high excess air and high stack temperatures because the seal between the boiler block and the steep base box crumbles away and there isn't a practical way to seal them once they are built in the factory.

And that "H" control with the long capillary tube has surely failed. The tankless Coil was never connected. Many of us tighten down the flange bolts upon installation when new.

Must have been a low price quickie change. Preventative Maintenance wasn't included in the price. Nor was it offered as an extra.

billtwocase

Definitely an Ultimate boiler originally out of Natick Mass. I "used" to instal many of those, just didn't know they made a dry base boiler, or never looked into one. I think that coil is definitely not replaceable, and those bolts break easy enough when there is very little rust. Not a good cold start boiler, unless it is a block boiler. I will echo make sure a heat loss is done, and 3 pass is the way to go.

historicalwork

A quick thank you for all the feedback so far. I appreciate hearing a little bit about these boilers in terms of the type and quality. While there were a a lot of service tags hanging on one of the pipes when we got the place, it isn't clear how we'll the boiler was maintained in the past. I suppose it doesn't at this point. I've taken a stab some of the heat loss calculators I found online and my very, very rough calculations suggest about 135k btu. That seems to match up with one of the estimates I got where they measure the square footage and the length of baseboard heating, etc. I am still curious if anyone has any strong reaction about the Carline burners. Thanks again.

billtwocase

I think Ice likes Carlin. He may even be their poster child . I do on certain units

icesailor

I like whatever works. Carlin's and Riello's work nicely on ones that don't work nicely.

historicalwork

I wanted to see if I could gain some more knowledge on our boiler. To continue our story, I've had three contractors out with estimates. No decision has been made. Two of them seem to be basing things on the measurement of the existing baseboard throughout the house. At least I think so because I don't think any of them have gathered enough data for heat loss. The other gave a "rough" estimate and said they would do more sizing when we commit. I also didn't get an details on the boiler model. So I'm not thrilled with that approach. One of the first two brushed off the idea of an outdoor reset. The other, which estimated a buderus G115, didn't included it in the estimate. I'm still not clear from my reading if the cost of the logmatic control is worth it for my needs.

I did spend some time with the Slant Fin heat loss calculator. I doubt all my inputs are correct but I get about 133K btu/hr heat loss. We are in a ~ 100 old solid brick house with some replacement windows. We have about 3,500 sq ft (across four floors - attic and finished basement areas) that's heated. I'm trying to work on the air leaks when I can. I'm reading what I can on boiler sizing and learning how they get over sized. The label on our current boiler indicates a net IBR Rating of 160K Btuh and IBR firing rate of 1.65 GPH. But it also shows a "Recommended Economy Rating" of 108K Btuh and "Economy Firing Rate" of 1.10 GPH. I'm not sure I'm clear what that means. I should add it also has a Enertrol Model HWRO-SS. I traced a wire that goes outside to what looks like a temp prob. I can't find any instructions on the Enertrol. It's in Std mode now. It made me wonder how I know if it's even working - despite having the boiler serviced each year. I am assuming the water temp would be down on a warm day versus a very cold day. But I don't know how that would be measured in the system.

I'm going to get some rough numbers on how much oil we actually burned the last two winters. I saw a couple posts elsewhere giving some rough calculations to get another angle on how much heating was required. I guess none of this is rocket science - at least not at the harry home owner level. But I like the idea of understanding the basics of what goes into the decision, sizing, etc. I do take to heart what many say about worrying more about the contractor versus the specific boiler. I do like all I read on the Buderus. But that seems to limit me to a couple companies and they are the larger oil companies in our area. Some contractors say they install them if needed. But, to me, i have to think it's best to get someone that knows the product.

In any event, the current boiler continues it's slow trickle onto the floor but it's manageable and - so far - that's giving me a little time to do research and get a couple more estimates. I found one place slightly out of our area and the guy really seemed to know the buderus products. He said he would consider coming out despite the distance. He was very strong on the logmatic control and being very careful about correctly sizing the boiler. I hope that pans out. It such a big investment and you hate to make a mistake on the purchase.... thanks again.

historicalwork

Just a quick thank you for the quick reply. I'm reading through your posts again. We are in Virgina (northern). Your response gives me the confidence to pass on contractors not doing what's needed. On the burner, the last card left by the service guys seems to indicate the burner is at 1.1 gph. It's handwritten. I'll look again in the AM to see what details are shown in the beckett burner. Another point, the house has three zones - one for basement, one for 1st flr, and then (unfortunetly) one serving both the 2nd floor and finished attic area. However, related to sizing, it's rare we keep the basement area heat on above 55 degrees since we rarely use it - the basement is really three room areas and then a third area for the boiler, dryer/washer, etc. With that said, does one consider the fact that all three zones or all of the house would not be heated to 70? And thus we would have a slightly lower heat loss number?

icesailor

@historicalwork:

Some boilers by some oil boiler manufacturers (like Peerless WB's) come with multiple ratings for the same boiler. Depending which nozzle you choose to put in it. Other boiler manufacturers like Weil-McLain just have one maximum firing input. Astute installers down fire them for better efficiencies when possible.

No matter what you get, you need a accurate heat loss calculation done. The Slant-Fin is a very good heating program. You will easily get within effective hand grenade range. Much more accurate than the old pencil at arms length standing 100' from the house with the sun behind your back.

As one who has worked both sides, we get tired of tire kickers or people just shopping for the best (lowest) price. It takes hours of uncompensated time to do a heat loss and all the take-off's for a new heating system. Then, not get the job because some slug says to you "Whatever anyone says for a price, I'll do it for $300. less. guaranteed. Some of us resent figuring and pricing out our jobs for our competition. Or partnering with Internet Retailers or HD or Lowes.

Robert O'Brien

"We can reserve judgment until he arrives. It all depends if he is willing and able to perform a proper heatloss on the building."

Are you willing to pay for it?

icesailor

Dan wrote a column years ago. About a guy that offered "Free Estimates". The estimate for free was quoted at anything from $100 to $10,000. When the prospective client asked, he was told that that was for the "Free Estimate". A fixed price cost more because of the time involved in doing it properly. And if he got the job, the price for the fixed price would be included in the price if he got the job. That got the prospective customers attention. Because THAT guy put more skin into the game and the customer had a reason to remember what he was getting.

I think there was also an issue of giving out specifications and the customers passing out all the free information to prospective bidders and having all their work done for free.

Something about the stinginess of someone who pays for an Ice cream cone, isn't going to go out and share it with the world to find out some place to get a tastier or cheaper ice cream cone.

I wish I still had a copy of that article.

historicalwork

So much helpful information - I'll try to respond to each post.

Hatterasguy - thank you again. I appreciate the clarification around the boiler firing rate and the output. That makes sense. No, I can't recall over the last couple winters we've been here where we couldn't heat the house. I recall the boiler being on a lot more often but never ongoing, although I would be paying attention to it now. I'll check the charts for the design temps - with my limited knowledge, I see the option to enter the "Outdoor Temp" in the SlantFin program and I assume that is the design temp (e.g. 16)? Appreciate the input on the basement. One area I didn't know how to handle in the SlantFin program was our attic. Is is essentially a finished attic space (well insulated as it turns out) in the hip roof. Meaning, as I see it, there is no exterior wall area since even the knee wall built out from the roof. So, in the program, does that mean you enter no perimeter wall and only note the cold ceiling/roof? Not sure if that makes sense.

icesailer - I can totally understand your perspective on tire kickers. I work in a different industry but I'm sensetive to the time spent estimating and giving out information. It's a tough balance. I even put together a quick sketch of the house with room measurements and basement (pipe are with fins) measurements to save them time. And I'm not after the $300 as much as I am someone that instills as sense of confidence around the product, the care taken to size the unit, etc. I am so worred about shelling out X dollars and finding out it was done wrong. I'm trying to find area neighbors that have dealt with some of the companies to get feedback. And, I'll admit, I'm sure I'm over thinking it all. I've got another smaller contractor coming out today. We'll see what that yields.

Robert O'Brien - funny you say that, I was going to offer paying him for an hour or two of his time. But he emailed and was honest to say it's a bit far and their busy. I can respect that. He provided another reference and I'm following up on that.

If I could ask another loaded question, a few guys I call say they sell X boiler but say they install many others when needed. Say, for example, they sell Dunkirk but say they've done a few Buderus. They go on to say they are very experienced as mechanical / heating contractors and have enough experience with oil boilers / water heating systems to deal with most all manufactures. Is that a fair view of things? Meaning, does a contractor have to put in 100's of a certain brand to really install correctly? Or, can a competent contractor do the install of a brand they don't carry. If I guy picks up a Buderus G115 with the logmatic control and only put in two in a year, does that scream problem? Or is that too open ended of a question?

icesailor

@hatterasguy:
@historicalwork:

Knowing and understanding how heat loss programs work helps in their understanding.

In the case of a second floor room with a unconditioned but enclosed space above like an attic. Although it may be zero outside, and 70 degrees in the room being heated, the attic space is assumed to be 1/2 the difference (35 degrees) so when you do the ceiling loss calculation, you correct it to 35 degrees, or half the heat loss. Knee walls are the same. But cathedral ceilings and slanted ceilings next to knee walls and flat attic ceilings are treated as an outside exposure.

With the old gray H-22 heat loss guide, they used two methods. The Detailed method and the Modern Method. Both methods will give you close to the same results. There were more computations and measurements in the Detail method. The Slant/Fin program uses the "Modern Method". If you have it loaded into a Laptop computer, and you are experienced, you can walk through the average house and do the numbers in 1/2 an hour. If you are doing an addition to an existing system, you will know what each and every room has for emitters and how they relate. After a while, you get an understanding about what and how the old dead guys did it.

And when the customer sees you measuring and computing, and say to them, "Say, this living room is a little short on radiation compared to the other rooms. Is this room often cold?"

Why yes, it is. Don't think potential customers don't notice that you were the only one that took the time to go over the most important financial investment of their lives. Which no one else could be bothered doing.

Hatterasguy:

You have all your ducks. They can line up better.

icesailor

"" It's a heated "attic". You use the full 70 degrees. ""

If the space above is heated, you don't deduct heat loss in the room below. we're not talking about the same issue.

Steamhead

HistoricalWork- have you tried Dan Foley, of Foley Mechanical?

icesailor

"" He does not use a temperature of 35F as you have suggested. ""

Without getting snippy, if you knew how the program works, you would understood what I was saying.

Once again, all the tables are based on a 70 degree Delta T. -0'F outside and 70'F inside. Once ALL calculations are done, you correct for your local conditions. Because the program uses a 70 degree Delta T, and all data is based on it, if you have a room that has an exposed wall, the factor is 70. Because the OAT is calculated to be Zero, the inside at 70 degrees. If you have a room like an attic above or a knee wall beside, it is calculated that the inside temperature in the unconditioned space will be 1/2 the Delta T, or 35 degrees inside the unheated space. Air has an insulating/resistance value. That's why a window assembly with a single pane, double hung window with a storm window on it looses less heat than a double pane insulated glass window like Anderson Thermopane windows. Only when you add a third panel will the window loose less heat.

And you can't just take a wall unit with windows and give all windows the same factor. Because in an uninsulated wall, the window is more resistant to heat flow where the same wall, insulated, will allow more heat flow.

If the wall space lost 10,000 BTU's per hour, you would correct it to 5,000 BTU's per hour. If you need 10' of baseboard to cover the wall, you only need 5'.

That's where the 35 degrees came from.

If you get the H-22 IBR/AHRI heat loss guide book, and learn it, you will see that this is how the Slant/Fin program works. There are no shortcuts. You have to do the whole entire thing.

SWEI

Some heat loss programs don't allow you to adjust outdoor temps on a per-wall basis. For those, we just halve the wall or ceiling area as needed to make the numbers come out right.

icesailor

Well, like I said long ago on this. IBR does, ACCA Manual J ones don't because they are based on AC and the dropping OAT is a plus.

Almost any house I ever figured, wasn't a box. It was a cut-up pile of little boxes with roofs that had shed dormers on one side and dog house dormers on the other. Sometimes with 4 outside walls. I never had a cold one.

I DID spend a lot of money on ACCA Manual J based programs to try to get away from the H-22 guide. The IBR/Slant Fin program was proprietary to the Hydronics Institute. They wanted a piece of the action using their methods. Some employee developed a WIndows based version that was over $500 and difficult to use. With the collapse of the Hydronics Institute, Slant Fin must have bought the rights to the concept. I don't much care how anyone else does it. Or understands it. When I saw the duct board, round flex ducts AC guys started throwing all their AC systems with the side part of heating, I was appalled at the messes. Rooms that had all the ducting in unconditioned attic spaces that froze plumbing in the winter with summer time air outlet temperatures and summer temps perfect for the winter time.

Heating is heating, cooling is cooling.

historicalwork

I hope I haven't explained our situation in the wrong way. If it helps to clarify, our house is a typical four square style with a hip roof. The attic was finished w/ small windows in the dormers on three sides, a closet area on the other side, knee walls elsewhere, and it has two hot water registers for heat (pulled off the floor below). They left a small area at the very peak - there is an attic hatch that leaves maybe a pyramid shaped area about 8' x 8' and maybe 3' high at the peak of the hip roof. So, walking around in that finished attic area, you have an area in the middle that's flat (the unfinished attic above), some slanted / sloped areas that follow the roof, and then down to the knee walls. I hope that helps describe the situation. It occurs to me that in the heat loss program I should maybe consider the finished attic as another floor and then add in the smaller attic space above in the peak of the rook? I don't know if that changes anything in the discussion. I find the discussion of heat loss interesting and so I wanted to add what I could.

icesailor

All aircraft fly to a place that they can land at.

Its all semantics in this discussion.

I'm talking about splitting hairs. In practice, I always called rooms with unheated spaces over them as exposed and used the higher number as a fudge. Often the difference was equal to less than a foot of baseboard. Who's going to cut down baseboard. Just go to the next normal size.

To some of us, our main consideration was always an equal balance among different rooms. That when you went from one room to another, the temperature felt the same and there were no drafts.

If you are adding on to an existing structure with heat, never try to balance the new to the old. It won't work. Which you quickly find out when you do a complete heat loss on the old structure and compared installed radiation. Then, you wonder what the old dead guys were thinking.

historicalwork

@Steamhead - FYI I called Dan - thank you for the reference.

historicalwork

As a follow-up, following advice of many, we are looking at several estimates. I have what may be another difficult to answer question. Most all contractors have recommend replacement of things like the expansion tank, water feed valve, circulator pump, etc. Some have gone further to suggest replacing the existing zone controls - swap out three zone values, the wiring /transformers and replace it with circulator pumps that I assume are controlled through some new panel. In these cases, it is really a nearly 100% new install of all components. From what I can tell, our zone controls are a 20-30 years old - but I believe they are otherwise working. They each run to a small transformer (I assume for the voltage change). Part of me can see the value in renewing the entire system, but it comes at a cost (how much I can't really tell from estimates). Is there a true downside to installing a new boiler but leaving older type zone controls? Is this a matter of preference or is there a material impact on performance/efficiency? Or, just good practice?

Lastly, I went back in to check all my heat loss calcs. It still all a very, very rough estimate, but I think the estimate for heat loss may be closer to 120K btuh. But again, I feel like I had to make a lot of guesses and assumptions. I also went through the possible output of the baseboard and convectors in the house and came up with a number that is in the same neighborhood as the heat loss. I'm sure my numbers could easily be off +/- 15K buth. On a related note, if it would even matter, how does one factor in the heat given out by the boiler if it's within the basement area? Our basement has four rooms - three heated and one not. The one that isn't heated with baseboard has the boiler. Is that still considered a heated room for design purposes? Again, I know it's all about getting in the ballpark, but I'm just curious how one accounts for these things.

SWEI

Replacing bad zone valves with good ones is OK. Replacing zone valves with circulators in this day and age indicates that your contractor hasn't changed his way of thinking in about 15 years and probably isn't the best guy for the job.

icesailor

Replacing Zone valves with circulators:

X 10!!!!

Just one of those circulators would pump the whole house. And they want to use how many of them?

The contractor that gives you a quote for changing just the boiler, with a whole list of "additionals" with reasons to change them will be getting the job. And it won't be the one that wants to re-build the world.

In my experience.

Some old dead guy I used to pal around with always said. "You have to leave a little meat on the bone for both of us".

historicalwork

Thank you. I read through a bunch of zone valves vs circulators threads and I'm not sure I could tell which side wins. To make sure I'm not using the wrong words when it comes to "Valves" and "Circulators" I attached an over simplified schematic of how the pipes are with our system. The only obvious point I would make is that all contractors talked about that in a multiple zone valve / circulator scenario, they would move the circulator to the out or supply side.

icesailor

You have two 3/4" Taco zone valves and one 1" taco zone valve. And one Grundfos circulator.

20 years ago, there were some really bad zone valves out there. Not today. Zoned systems use less pipe, fittings and materials. Where I worked, if I wanted to do a 6 zone system with circulators, I wouldn't get the job. Someone would put in 6 zone valves and the circulator that comes with a package boiler.

We all like to do what we are comfortable doing, and charging accordingly. Unfortunately, some are uncomfortable paying those prices so someone else does the job.

heathead

I have a dumb question is natural Gas availvble?? You said Northern VA. Even if you have to pay and run a pipe a small distance it is worth every penny.

historicalwork

Thank you re valves/circulators. No, we are a little ways away and gas is not an option for us - it's not far but it would take $$$ to get it and it's well beyond reach. I wish it was an option!

SWEI

An ECM smart circ paired with your existing zones valves (assuming they are working) might work well for you.

icesailor

Hatterasguy said:

I was skeptical of zone valves 10 years ago when I put nine Honeywells 3/4" in my own house.

Failed two motors in 10 years.............no valves.

I'm a convert for sure. One Taco 007 flows more than I need.

I would have been skeptical too if I had used Honeywell's and they did that. Fortunately for me, I saw everyone else have problems with the Honeywell's so I stuck with my more expensive taco's. I still had a few in that had the green heads working. Others that had green heads that were replaced by Gold heads.

historicalwork

We are closing in on a decision w.r.t our boiler - slight delay to get estimates on the chimney lining - but I wanted to ask another heat loss / hot water baseboard question. I know based on all feedback that boiler sizing should be based on the heat loss and not the length of hot water (fin type) baseboard (we actually have both baseboard and then some fin type convectors).

Out of curiosity, is there ever a situation where the length of baseboard can impact the boiler sizing? I may not have grasped the details correctly but I had a contractor suggest that not considering the length of baseboard could impact sizing because the heat loss in the baseboard could return water at too low of a temperature and (if I understood the point) that the boiler needed to have the capacity to deal with heating it back up to the proper temperature. I may not have that right - but the point was that he felt the output or capacity of the baseboard was a factor.

As an exaggerated example, say you have a house where the combination of baseboard and convectors could could put out 150K BTUH but the heat loss calcs suggest a heat loss of 100K BTUH. If the boiler is closely sized to the 100K BTUH figure, can the fact that you have a system "taking out" another 50K BTUH create problems? To me, as others have stated, even sizing to the heat loss calcs suggest the potential for oversizing given things like heat loss is based on a design temperature or it's unlikely all zones will be called at the same time.

In our case, based on my rough calculations, I don't think we have such a large gap between building heat loss and capacity in the baseboard. But I was just interested in understanding if there is any value in the statements this contractor made. To top it off, this contract said - as a result of his statement on the baseboard - that a heat loss calc isn't needed.

icesailor

AS I understand the basics of boiler ratings, the IBR/AHRI part is based on a 20 degree Delta T and 15% allowed for piping and pick-up loss. As long as the boiler is sized to the heat loss of the building, your worry should never be an issue. That's what the rating covers. Your installer should understand that. For the sake of discussion, without playing "fun With Numbers", if you needed 100' of baseboard, and a 100,000 BTU boiler covered the heat loss, so you added 1,000' of baseboard, it doesn't matter because the boiler will only deliver however much energy is needed.

As far as the return temperatures of the 100 or 1,000 feet of baseboard is concerned, that's what zoning is for. To make the circuits smaller so the Delta T isn't too great.

Again, for the sake of discussion, if Slant Fin #30 baseboard says that 10' of #30 baseboard, with 180 degree water with 140 degree discharging air through the opening with the damper open will give off 6,000 BTU's per hour, it doesn't matter what the flow rate is. It is putting out the listed amount of heat. If the room needs 6,000 BTU's per hour when it is zero outside, the baseboard is doing its job. If the temperature goes up to 35 degrees, the baseboard still gives off 6,000 BTU's, but the room is only loosing 3,000 BTU's per hour.

Common sense Short Bus Math.

If you turn the thermostat to 70 degrees, and the room stays at 70 degrees, you will be very happy.

historicalwork

Another related question if I could. Based on a lot of reading and research, I am very inclined to go with the Buderus G115. However, after getting the contractor heat loss calcs (Manual J) and doing my own (slantfin and HVAC-CALC) I get roughly the same numbers - about 110K BTUH at the design temp (12 degrees for us) for our area and using 70 indoor.

The question relates to sizing up or down... the heat loss would put me between the G115WS/4 @ 95K BTU IBR and the G115WS/5 at 119K BTU IBR. If I went by gross output for the 4 section, the output is 109K BTU - that would seem close enough given our situation and assuming fudge factors in the heat loss calcs. As refereence, the boiler sits in one corner of a semi-finished finished basement (three rooms have baseboard but are rarely used so the heat is set down and the boiler is in an area with washer/dryer). The heat calcs assume the basement is heated, etc. The contractor suggests the 5 section to be safe. I could go with the 4 section but I would have to request it. I feel after all my reading (including this forum) that the 4 section would suffice.

Any general advice in this situation?

historicalwork

"BTW, your plumber doesn't understand hydronics in any way." - yeah, I opted not to go with that contractor! I appreciate the information. Like so many things in life, you wish you had more time to understand them and, because you don't, you grow to appreciate those in the trade with the needed expertise. But it's still nice to know enough to guide things to some degree. I feel like I'm almost home on this project - just deciding the up or down sizing question at this point (G115/4 vs G115/5).

historicalwork

Hatterusguy - in reviewing the Buderus literature, they indicate the 5 section is at 1.1 GPH - would that matter too much in your mind? Or am I splitting hairs between the two models? What frustrates me is our current boiler has a 1GPH nozzle. But then I read some info that indicates you have to look at both the GPH and the pressure on the burner? In my simple mind, if the current less efficient boiler is at 1 GPH and I'm replacing it with a more efficient boiler at 1.1 GPH, I'm going up in size. And I can't say we have had any problem heating the house over the last two winters. - even on the coldest days. Again, perhaps I'm worrying too much about subtle differences?

historicalwork

Yeah, and it's hard in my mind (given no experience) working with the various entries in the heat loss programs. For example, our house is solid brick with plaster, but I haven't come across any of the basic programs (even with HVAC CALC i purchased) that have the exact options for that wall type. And, for example, as described above, we have an attic with a somewhat irregular shape. So, I could see how the numbers could swing either way.

SWEI

When you did your heat loss calc, what did you use for your window U-values? If you picked something out of the software, it almost certainly assumes your windows are uncovered. How often are your windows uncovered on the coldest day of the year in the middle of the night?

historicalwork

I'm not sure if my response will make sense - but, in HVAC-CALC I simply chose the default values for construction - single pane glass w/no shading for the original windows and then double pane glass w/no shading for the crappy replacement windows. In the SlantFin program (using their terms) I selected a factor of .65 for the double panes and then 0.56 for the single panes with storm (most do have old storms and I put up a few home-made interior shrink film storms on the worst ones). In the trial of HeatCAD I used R1.1/U0.9 for single panes and R1.8/U0.57 for the double pan windows. And, to your point, we do have roll down shades in the bedrooms and curtains and curtains on most other rooms like in the family, dining, etc rooms.

SWEI

If you re-run your calcs using lower U-values to reflect the drawn shades, I suspect you may find that the 4-section boiler becomes a near-perfect fit. These calculations already include fudge factors for several areas.

If you employ ODR and constant circulation using the mixing valve suggested above, you can also eliminate the pickup factor assumed in those IBR numbers (which are based on a cold start configuration.) As long as the boiler is not in a very cold location, you pick the correct weather data (don't ignore wind conditions if those differ from the standard data) and don't employ deep setbacks, you can comfortably get by using the DOE numbers.

Remember that ASHRAE design conditions only happen 2.5% of the time on average. The rest of the time, the boiler is oversized for the task. When we have a job that's on the edge as far as sizing goes, we re-run the calcs for a series of different assumptions (raising and lowering the design temp outdoors and indoors, with and without thermal drapes or cellular shades, etc.) Are you willing to accept something like a 66°F indoor temp for 2-3 hours in the early morning two days a year in order to have a happier boiler and lower oil bills the entire rest of the season?