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Preparing ahead of time for a boiler replacement...

MTC Member Posts: 217
I've done a good bit of work on steam systems, but never replaced a boiler or anything like that, and done very little on hot water systems, but now I find myself owning a property with an aging HydroTherm boiler with CI radiators, just waiting for the problems to start, and want to already have a full plan for when it happens. Maybe I'll even get ambitious and just swap it out next summer if it makes it through this winter, who knows.

Anyway, I'm sure you're all sick of these types of questions, but I'd like to get your recommendations for new equipment, as well as some sizing stuff, etc.

House is about 1800 sq ft, about 100 years old, has had walls blown with cellulose and attic insulated pretty well, among other odds and ends attempts to seal things up. Piping is all nekked, but I'm in the process of putting together an order of 1" molded fiberglass for all the mains and larger risers, the 3/4" and some of the 1" pipes I just did with the self stick Home Cheapo pipe insulation. Should be sufficient, as I don't want my basement to be an icebox, so not looking for maximum heat retention, just good control.

I've only owned it since late March, but seems like the system was heating the place nicely, the old lady who lived on the first floor apparently kept it very warm. I've sealed it up better since then.

So, first thing I need to do is do a heat loss calculation, which I have to figure out how to do and then get it done (never had to do those before). I know the existing boiler (HydroTherm HC-125, 125k input, 100k output), is oversized now, and likely was before insulation values went up. Guessing I'll end up needing more like 80k output.

There are 2 mains, one longer and one shorter, both start as 2" and work their way down. I have approx:

42' of 2"

16' of 1.5"

40' of 1.25"

80' (?) of 1"

lots of 3/4" risers

Longest run is from basement floor in one corner to 2nd floor radiator, about 140' total loop.

Current pump (only one, no primary/secondary or anything like that on this system) is a Taco somethingerather with a 1/12 HP GE motor.

I plan to repipe according to Dan's piping recommendations in Classic Hydronics, currently pump is on return, comp tank off top of boiler with small auto-vent and no separator, unless its built into the boiler under the vent.

So, I'd like people's recommendations on:

Boiler brands

Mod/Con/ KISS

Air separators - types/brands, etc...

Dirt separators - worthwhile, esp in an old system like this? You pipe it on return near boiler, right?

My interest is to keep maintenance low, system longevity high, and costs (primarily long term costs, but upfront is always a concern as well) low. Not sure what balance to use of new tech bringing higher efficiency vs simple old setups that are a lot cheaper up front and tend to have less issues/last longer, but higher op costs...

I plan to own the building longer than this boiler will last, fwiw.

In the meantime, anyone have access to a service manual for the HC-125? I only see newer ones, all with a letter modifier, available online, but I might not be looking in the right places. I'd like to do the basics... clean the burners, exchanger, etc, on this one before winter. Will try to post a few pics of what I have soon.

Sorry for the book... I don't know how to be short-winded :-P


  • Rich_49
    Rich_49 Member Posts: 2,766
    edited September 2013

    I would suggest that you use what you have to your advantage .  I Would certainly stay away from a low mass heat source with small HX .  If you do go that way make sure you have a quality dirt elimination device , Caleffi SEP-4 would be a good choice .  I recommend an HTP Pioneer (PHR100or130-55) . Dirt elimination becomes less of a problem also with this equipment for obvious reasons . A quality air separator only would suffice . This unit has a 5" center tube and 2- 1 1/8" spiral tubes that make up the heat exchanger , no small channels that will require loads of maintenance and nothing to be compromised . No Primary / secondary required , ODR is a snap , really allows for the KISS method you are looking for . http://www.htproducts.com/literature/pioneerbrochure.pdf . Sounds to me as if the head losses will be minimal due to the pipe sizing , you only have to make sure that you overcome the highest head loss but be sure to pump adequate GPM . On a system such as yours , if it's 100K , 5 GPM would be good since the radiators will function real nice at a 40* Delta T , this should keep you condensing even at design day conditions . My personal choice for a pump would be a TACO 00 VDT (008-0013) or if head loss allows the Bumble Bee is best ( electrical savings also) , set whichever to 40* and you should be good to go . 

    The Pioneers cost in the middle range between cheap combis and higher end wall hungs , it is really versatile . Due to the materials used in construction it should last longer than many of your other choices , with a little maintenance quite possibly a couple decades , maybe longer .   Check it out and hope this was a help .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC
    Serving most of New Jersey, Eastern Pa .
    Consultation, Design & Installation anywhere
    Rich McGrath 732-581-3833
  • Paul Pollets
    Paul Pollets Member Posts: 3,656
    Having your cake and eating it...

    If you want to do this once, and addressing all of the concerns, then your system will have:

    1. a better modulating boiler; either a Viessmann Vitodens or Triangle Tube have a track record of reliability and service support.

    2. hydraulic separation (Low Loss Header or equivalent)

    3. Replacement of existing radiator valves with thermostatic radiator valves (TRV's)

    4. Using a variable speed pump on system (Grundfos Alpha or Taco Bumblebee)

    5. Add an Indirect DHW Tank to provide potable hot water

    6. Insulation of "near-boiler" piping

    7. Replacement of expansion tank with bladder type tank (Extrol 60 or 90) and installing the tank to allow "pumping away"

    8. Cleaning system with proper boiler chemicals on commissioning

    Missing any of these items will affect either performance or efficiency. Choosing the correct boiler is difficult, when you aren't involved in the trade. Be skeptical of glossy brochures. Mod-cons can be either good, better, best or not so good. A quality appliance installed incorrectly will not be good. There's no such thing as allowing budget to determine best practices. It costs what it costs to do it correctly.
  • MTC
    MTC Member Posts: 217
    Thanks guys, some followup questions...

    Will have to look into boilers more... looking at circulators a bit, and thinking about my system... Using the rule of thumb of 4 ft/head/100 ft piping +50% for fittings, etc, I would have about 8-9ft of head to get to furthest radiator (140ft x 6/100ft).

    I know the rule of thumb starting point for most systems is 20 Delta T, but also that some systems seem to run better on higher. An all CI radiator system you would say should be around 40? Can you give me a quick/easy explanation why (not arguing, just trying to learn)? In sizing, should I size things to handle more like 20 to be safe, then I can dial it in anywhere in that range if necessary? This seems to make a difference in the options for circulators.

    Haven't done heat loss calcs yet, but I'm thinking that with added insulation, the fact that the system seemed to be happy to overheat the space (due to high tstat setting) before that, etc, that my actual need will be more like 80k than the existing 100k btuh. So for 20DT, that would give about 8GPM, vs 4GPM for 40DT.

    The bumble bee curve shows that at max speed I'd get 6GPM at 9 ft head, which puts me right between those 2 flow requirements.

    I wrote down a stamping when I was looking at the boiler/etc - one of the flanges is stamped 110-338 on the circulator, so I guess this is an older Taco 110. Looking at specs on the new ones, they have a max head of 7.5, but flow of up to 33GPM. I don't really know what conclusions to draw from that, but the system seems to operate well with it from what I know. Can I assume from this that 7.5 ft of head would be more than sufficient? The bumble bee that you both seem to like would give me almost 8GPM at that head.

    Also, is there any merit to the thought that higher pressure pumping helps balance out a system like mine, where there are no zones or anything - enough pressure forces water to get to the higher resistance radiators? Would a smart pump/higher DT w/ lower flow rate possibly create balance problems that didn't exist with my old on/off pump?

    As for dirt/air separation, the Caleffi you mention Rich is a hydraulic separator, right? I'm not sure I understand the purpose/benefit of these in general, but particularly on a system w/o multiple pumps. Is this something I need? Any thoughts about the Spirovent separators (sep air and dirt ones) or any other brands, if I don't need the hydraulic separator? The boiler you recommend Rich also claims to have built-in air and dirt separators - are these reliable, or is it recommended to put in external ones as well?

    As for TRVs, having managed a number of steam heated apartment buildings, using TRVs in some cases, and not in others, I'm not sure that I'm a big fan for this application. In a private residence, they're great - allows you to balance the system just how you want it. In apartments, I've found that every single TRV was turned to 5 (max on the Danfoss' we used), even if it was uncomfortably hot in the unit. This screwed with the balance of the rest of the system. Most times I found it better to take out the TRVs and put in fixed vents of the appropriate size to get the balance I wanted, and not give the tenants any control over it. I assume that they'd function somewhat similarly on a hot water system, but I'm not sure.

    Insulation is a given - I'm in process of getting all the mains insulated before winter. This will include near boiler piping, and then i'll have to redo the insulation on the near boiler piping i guess when the new boiler goes in, but it will all definitely be insulated.

    Are indirect water heaters really that big of a cost savings? I've been wondering about that for a while. I can definitely see how they would work well in the heating season, but does running a boiler all summer to provide DHW really pay off?

    Existing tank is a bladder type, i'd replace it with a new Extrol regardless. On a system this small, wouldn't a 30 be sufficient? Certainly seems like a 90 would be massively overkill, but maybe a 60 due to the high water content compared to today's systems of similar btu usage, but a lot less water?
  • MTC
    MTC Member Posts: 217
    edited September 2013
    Some pics of existing boiler

    if that's helpful in any way.

    Also, I labeled the pics backwards for some stupid reason... the diagram is correct, but the pictures the supply and return labels are reversed, fwiw. Didn't seem worth redoing it...

    Also, fwiw, I didn't think of it until I was sketching out that rough diagram, but there are 2 baseboard heaters in the house. The far right of the sketch is in a later addition, they piped to a BR rad, then in series to a bath baseboard, and a baseboard in the storage room under the addition. They were having trouble with the pipes freezing under the bath, so they added heat here. I've had the plumbing and insulation redone since then, so was thinking of modifying this slightly, leaving them piped in series (not ideal, but seems to be working and they're in right order of priority), but adding a jumper between supply and return of the basement heater with a valve in it... this way you could close the valve and get full heat to basement rad, open it and essentially bypass it, or leave it in the middle somewhere and get partial heat, as needed. Any thoughts about that?
  • MTC
    MTC Member Posts: 217
    Relief valve blowing on heat up

    Hey all,

    I've been busy with other work on the property, so set aside my replacement planning for a bit. In the meantime, I've taken apart the old boiler and cleaned the burners and as much of the heat exchanging surfaces as I could get to. Burners were caked in rust, but the exchange surfaces were surprisingly clean. Anyway, I've also insulated all the basement piping with 1" fiberglass on everything 1" and larger, and Home Cheapo stuff on the little 3/4" lines. Don't want to overdue the insulating, as there is no real heat source in the basement.

    Anyway, fired up the boiler a few days ago for the first time this season, all seemed good. When I went back into basement later, the relief valve had been blowing. It def never blew before heating cycles started, and doesn't seem to continuously blow. I haven't stayed around to watch exactly when it goes yet, but will try to do that today. I just turned the system off temporarily so that it wouldn't keep doing that until I could work on it.

    I'm thinking the relief valve is operating ok, as it only blows under certain conditions, unless they can get "off" as they age and blow at lower pressures. Nothing has changed from last year (other than cleaning and insulating), when system was running fine. So is my water feeder pumping in too much pressure? The insulation adding enough extra heat to boiler to blow pressure valve? Valve just faulty? Bladder tank failed?

    Boiler is set up all wrong, hoping to avoid messing with it much until I redo the whole system... Got pump on return pumping directly into the boiler with auto feed right next to it, and the bladder tank, auto air vent, and relief valve are mounted on top of boiler. Thats pretty much it, its an old school boiler without much on it.

    Other caveat, there are NO valves on this thing. No valves for the pump, none to isolate the boiler or controls, most of the radiators don't even have them. Again, I plan to add valves to isolate the pump, boiler, etc when I redo the system, but for the meantime, is draining the whole system the only way to work on this stuff? I really hate to introduce all that new water to such an old system any more than I absolutely have to. I guess if it comes down to draining the thing for this, I should just put in a main valve on supply and return sides so that I don't have to drain whole system again to replace boiler etc in future.

    I don't trust the guage on there, as it is quite old, but will try to see if it gives me any kind of readings on cycles today.

    Thanks for any help you can give. I need to get this thing back up and running for the winter, then can start planning my full replacement for over the summer sometime. If anyone has any more input on the books of info/questions I posted in above posts as well, that would be appreciated, but not as urgent. Thanks!
  • MTC
    MTC Member Posts: 217
    Update after some fiddling today...

    So I discovered today that my 100k btu output boiler has been operating for who knows how long on an Extrol 15 (or an older equivalent). It should be at least a 30, if not 60. I can't figure how the system survived all this time on that small of a tank..

    I replaced the temp/pressure gauge. I had it out of the boiler and it was reading 14PSI, so it was def not trustworthy.

    Was going to replace relief valve, but couldn't get the old one to budge, and with new pressure gauge installed, determined that it is in fact blowing right at 30PSI and resealing once pressure drops. For now I'll leave well enough alone, but have a new one on hand if it comes to it.

    Not sure if fill valve is working totally properly or not yet, it seemed to be filling up to its set pressure reasonably well and staying there, but I wasn't patient enough to watch it too long, wanted to start fixing things. So I got the system filled and bled all the rads, and then turned off the infeed water for now. System still blowing the pressure valve. It couldn't get the water over 110 degrees from cold before taking pressure from around 15 to 30 PSI.

    So, next order of business is a new tank. On my 125k input, 100k output boiler, should I go with the Extrol 30 or bump up to the 60 to be safe? One caveat that makes me consider keeping it to the 30 is its mounted horizontally, so bigger is more stress on fittings/tank/etc. When I get around to doing full boiler replacement, I'll move it up vertical under an air separator, and would like to use the same tank, but in the meantime, would a 60 be too heavy to mount horizontal? Would it be overkill for the size of my system?
  • MTC
    MTC Member Posts: 217
    One more question...

    So I"m a steam guy more than water (by experience, not necessarily preference). I'm not used to working on these systems full of water where opening the system is such a hassle.

    Anyway, I was quite surprised today to find that only minimal water drained when removing some of the boiler components. Can someone explain how that works, when there are no valves to stop the flow? Is it simply the difficulty entrance for air to replace the water that makes 2 stories of full radiators above me not come rushing out the relief valve when its open, or the gauge fitting w/ the gauge removed? Does the pump impeller help resist the flow required?

    It was a pleasant surprise, and after I was done and bled all the radiators, even more pleasant to find almost no air their either (and they'd probably not be bled in at least a couple years).
  • Steamfitter66
    Steamfitter66 Member Posts: 117
    Start with heating load calculation

    Not a rule of thumb calculation....your actual heating load will probably be less than 60k, Your piping loss at required flow will be less than 2' head.

    If its a rental than KISS rules.

    If its your residence then Triangle Tube makes a very good mod con with good support.

    As far as water not draining it could be the magical effect of the cohesive property of water combined with a cold system that due to temp and barometric pressure was under the perfect amount of vacuum to hold the water in place...ie you got lucky.
  • MTC
    MTC Member Posts: 217
    edited November 2013
    Thanks steamfitter

    for the reply. I need to figure out how to go about a heat loss calculation, never done one before, as I've mostly done repair work on steam systems, not new systems. Will start to work on that.

    Wow, less than 2' head? Is that just b/c of the very large piping? Using the quick rule (6' head per 100' of longest run), i get about 8-9', but that's probably based on more modern lower volume systems?

    This is a rental, 2 units with shared heating system where I pay the gas bill. So I don't want headaches and complications, but efficiency is good, as it keeps my long term operating costs down. Some of the simple boilers claim 84% AFUE, is it really going to save me that much in a smaller system like this to go up to the mod/con route? Enough to pay for the huge price bump?

    Also, is there value in running a simple boiler with an ECM circulator, or do you kind of need them both to add much value? Some of the pumps like the BumbleBee aren't all that giant of a price increase... if they improve efficiency, would probably pay for themselves quickly. And if you're right about having 2' or less of head, it would be way more than enough for my system's needs. Or do you think stick with a simple single speed circulator here as well?

    Any good resources to help an experienced contractor, but newb to load calcs, perform a load calculation? I just found SlantFin's app for Android phones, gonna give that a try... seems decent, but any better suggestions are welcome.
  • MTC
    MTC Member Posts: 217
    Heating Load Calc

    So I used SlantFin's Android app load calculator today at the building... not too bad, though I have nothing to compare it to. Steamfitter was right on the money, my number came out to just under 60k BTU based on 5 degree design day and 70 degree heating. I found a range of 5 to 11 for Pittsburgh design day temps, so went with lowest, and I plan to heat to 68, but gave a little room for cushion. The program didn't let me change the system temp from 180 degrees... my system currently doesn't ever seem to reach 180 degrees, but that may partially be b/c it is oversized and shuts down before it can get there. Or the high volume of water just makes it take a lot longer to get there... or both. Do I need to make any adjustments to the calculation to account for this, or is it good as is?

    I also had to make some educated guesses about some of the infiltration, insulation levels, etc. I've done substantial work to the place, so I've seen enough to have some confidence in my guesses, but can't be positive about some things. I tried to be a tad conservative when I didn't know for sure.

    Also installed an Extrol 30 equivalent today. System still gets up to 30PSI after running a good while, but it definitely took a lot longer to get there, and system got up to about 150 degrees instead of not even 110 like before. This was with reducing valve open, which is still a questionmark... maybe its leaking through a bit. Will run the system for a good long time again with the valve closed and see if its any different, just didn't have time to do that today.

    Any thoughts about a good boiler/circulator combo for this system? I won't be doing the boiler until at least next summer hopefully. I have only owned this building since spring, and would like to see how it does fuel usage-wise with the current setup, after sealing up the building and insulating the basement piping, etc. Then I can be a little more confident in whether or not the mod/con route is worth the cost, or if fuel bills are likely to be low enough to not justify it...

    Smart circulator (BumbleBee) with a "dumb" boiler any good?
  • never

    Never have a furance company do the boiler replacment.. same goes for plumbers... btw, I'm a plumber with hydronic heating experinces
  • Steamfitter66
    Steamfitter66 Member Posts: 117
    sorry I lost track of this post.

    It sounds like you have air in the system if its taking longer to warm up.

    As far as boiler sizing water temp is only relevant if piping is running through unconditioned space.

    Your lower water temp is because of oversized radiation and thats good. Cast iron radiators where sized for 140* water on gravity systems.

    I would Install a Triangle Tube prestige boiler with direct piping and a grundfos Alpha set on the low speed and check DT. If you install a mod con you need a combustion analyzer.
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