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Replacement System Design - Feedback Requested

skybolt_1 Member Posts: 16
First of all I'd like to give a huge THANK YOU to all of the contributors on this forum (and to the Holohans for founding and hosting it) for all of the many insights that you've given me in the lead-up to this post, and hopefully have gotten me 99% of the way to my answers from all of the content that I've read through here in the past couple of months.

I have a failed Burnham V73 105 MBH with a 1993 date code on it (big crack in the center section of the heat exchanger) in a 1977 single family gambrel located in Groton, MA. The house has 1,992 total square feet of heated space with 768 square feet of finished (but unheated) basement. There are three heating zones with standard 3/4" copper fin tube loops in the home, with the following measurements:

- 301" of finned tubing, 1479" total tubing length (including elbows/45's equivalent lengths), 16,120 BTUs/Hr
First Floor
- 408" of finned tubing, 1700" total tubing length (including elbows/45's equivalent lengths), 35,762 BTUs/Hr
Second Floor
- 472" of finned tubing, 1773" total tubing length (including elbows/45's equivalent lengths), 14,778 BTUs/Hr

All BTU's per hour are based on the SlantFin Heat Loss Calculator web tool, using U-Factor of .07 for the exterior walls, .15 for the unconditioned basement ceiling / first floor floor and .65 for the double-paned windows, and .05 for the top floor ceiling. 70 degree / 1 degree based on location.

The current heating system is set up badly, really poor piping layout and set up to "pump towards" on the return on all three loops, with dedicated circulators on each. Chimney was lined with stainless 3 years ago when I first moved in. I am looking at the Burnham MPO-IQ84, the Burnham V8H3W, and the Weil-McLain WGO-2 as replacements, given that I've seen / heard significant short cycling with the V73 in my time here and with a total BTU/Hr of 66,660 max I really don't need much boiler even if I end up adding a zone for hot water or the basement (or both) in the future. Plus, we supplement with wood heat throughout most of the really cold heating season.

Attached is my current system replacement design. I'm moving from three circulators to one Delta P unit controlled with zone valves and incorporating a boiler protection bypass controlled by a Caleffi ThermoProtec valve. Interested to hear the community's feedback in terms of whether this is a reasonable design given the above scenario.

Thanks in advance!


    EBEBRATT-Ed Member Posts: 14,505
    My only question is what is the pipe at the top of the supply coming out of the boiler? A manual vent?

    If you heat loss is right you should be fine
  • skybolt_1
    skybolt_1 Member Posts: 16
    Yes, that is the manual vent, same as shown here on page 50 of "Pumping Away" used for the initial air purge.

    Hard to tell whether the heat loss is "right" (can't see the insulation job behind the sheetrock), but I spent the better part of a Saturday doing all the measurements and plugging it into the SlantFin app and got the 66,660 value. Given that the Burnham 105 MBH would short cycle pretty badly my gut tells me that number is a lot closer to reality than 105,000.
    EBEBRATT-Ed Member Posts: 14,505

    Sometimes you can take some electrical outlet covers off and get a look inside the wall.

    Or cut a small hole in an outside wall under the kitchen sink, or in a closet.......somewhere it won't be noticed and cover it up with a blank electrical box cover and a couple of plastic anchors

    Just as a rough check I came up with 98 feet of finned baseboard based on your measurements. @600btu/foot=98 x 600= about 59,000 btu/hr so it looks like your ok if your baseboard measurements are good and it heats ok now.

    That would make your old boiler short cycle
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,375
    edited June 2019
    If you're going with the MPO, good choice, you don't need 1 1/2" anywhere, just bush it down at the boiler.

    I also don't like the way the bypass and thermostatic valve for boiler protection is drawn.

    I'd put the dirt mag after the water feed so you can catch any fresh water sediment.

    You're missing a ball valve, or the proper Webstone combo valve which should be placed to the left of the tee where the expansion tank connects to the main supply.

    Also, isolation valves around the circulator, Webstone expansion tank valve above the tank where the water feed connects to the system.

    Your new boiler will also short cycle except during your colder days. May need a small buffer.

    To the pros, will the delta P circulator play well with a mixing valve for boiler protection?

    How much oil did you burn last year? We'll run it through the @Robert O'Brien spreadsheet/calculator for a quick guess, but I think you're on the right track.
    Keep in mind the MPO 84 & 115 are the same boiler except for basically nozzle/pump pressure, and baffle placement. So if for some odd reason you needed more btu's you could set it up for more btu's.

    You also will need to probably line the chimney for the 5" flue pipe, or go with a Riello BF and shoot it thru the wall (if possible).
    I'd stick with the chimney if you can control the draft, which will need at least a draft regulator or a "Neutral Pressure Point Adjuster" as taught to my by world famous oil burner superstar George Lanthier in his books, Advanced Residential Oilburners, and Riello OIL Handbook.

    Page 24-25

    Edit: I'd also pipe in for an indirect, which you can add when whatever you are using for domestic hot water fails, no need to upsize the boiler.
    An indirect and that boiler will definitely be cheaper to operate than an electric water heater, unless your electric rates are very low.

    Please don't let anyone talk you into the Weil McClain. Any triple pass boiler is so easy to clean over a pin boiler.

    Another option is always an Energy Kinetics:
  • skybolt_1
    skybolt_1 Member Posts: 16
    @EBEBRATT-Ed - Thanks for the tips. I've actually had some exterior walls off to replace siding / sheathing in the past so I am reasonably sure that all my insulation is R13 when it was new but I live in the woods and the previous owners had a lot of issues w/ rodents... so that R13 is probably more like an R10 or so depending on where you look. Thank you for double-checking my numbers!

    @STEVEusaPA Great catches - I went through and added the valves and moved the Dirtmag. Attached is my V2 diagram. After looking at it again today I am guessing that when you said you "don't like the way the bypass and thermostatic valve for boiler protection is drawn" you were referring to the fact that it appears to be a tee on the pressure side of the pump? I adjusted the drawing a bit to show the bypass is a branch off of the main supply line. Let me know if that's what you were referring to.

    Regarding oil consumption - I've burned approximately 575 +-25 gallons between 6/7/2018 and 6/18/2019. I wasn't aware that the MPO-IQ84 and 115 were the same unit w/ different burner and baffle settings, that's really good to hear / know!

    Chimney was lined with either a 6" stainless liner right after I moved into the house about 3 years ago. Looking at the MPO I&O manual it states that both the IQ84 and IQ115 require a minimum 6" round chimney, so I I should be OK? Or are you recommending 5" for a different reason? I already have a new Field Controls barometric damper on it with the V73 today, but not a draft regulator as described in that guide... are there benefits of one over the other?

    Regarding indirect water heater, yes, that is definitely on my list of potential future upgrades, depending on where the budget shakes out to I may bump it up and do it all in one shot.

    Also did a bunch of reading on pin type vs. triple pass and after having cleaned the V73 a couple of times, you don't need to sell me on the benefits of "easier to clean". What a PITA that was... Definitely going with the triple pass.
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,375
    575 Gallons seems light and puts you @ 30K BTU's.

    I only mentioned 5" because that's what comes out of an MPO, so 6" is fine-you'll probably have too much draft anyways.
    The one you have may be fine, but when adjusting that burner on that boiler, you'll need to be able to get the draft down to almost 0 at the rear measuring port, and +.02 (can't remember the specs off the top of my head) over the fire.
    On mine I went with 2 dampers, still had too much draft and eliminated the dampers and went with the "Neutral Pressure Point Adjuster".

    Also, without a buffer, outdoor reset will probably increase short cycling.
  • skybolt_1
    skybolt_1 Member Posts: 16
    @STEVEusaPA, I suspect why that is light is that we supplemented with wood pretty extensively, just short of 2 cords worth in a FireplaceX catalytic stove. I will read up on the Neutral Pressure Point Adjuster.

    Regarding a buffer, I would love to incorporate one into the design, but I am quite space constrained in the boiler room which doubles as a workshop, and already has my oil tank, water softener system, and water heater in it. I am not sure that I can cram a 50-gallon buffer tank, which looks like the minimum I'd need to get to 10 minute runtimes from the Boiler Buddy calculator, in there as well... but I will see what I can do. Wondering if perhaps omitting the outdoor reset may be worthwhile if it is going to increase short cycling.
    HVACNUT Member Posts: 5,469
    FWIW, my '72 built house had R7 in the walls. And aluminum wiring. I gutted everything and put in new R15 and copper wiring. That was in '03. Knowing what I know now about air sealing, I want to kick myself even though it passed inspection.
    A blower door test and a smoke gun will show you where you need to button up. Every little bit helps.