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Retrofit/upgrade suggestions

Hi everyone,

We bought a 2400 sqft house (in Michigan, built in 1925) a year and a half ago, and have been steadily upgrading the energy use of the house.  We've added attic insulation, blown cellulose in the walls, foam in the rim joists, insulated the 1/2 above ground basement walls, and worked on some air sealing with a blower door test (we're still not good, but not awful).  We have lots of old windows that I'm in the process of rehabbing, but that's going to be a lifetime job.

The house has an old boiler that's working fine (no CO, 77% combustion efficiency), so I don't know if I can ever make a rational financial decision to upgrade to a modern boiler.  However, there are a few things I'd like to change and I hoped I could get some input.

Some stats- boiler is 225 kBtu input, 180 kBtu output.  I think it used to be gravity fed (old expansion tank in attic and 3" mains in the basement), but it's been retrofited with a 1/6 hp circulator and one input and one output.  It's all on one zone with one thermostat, and there aren't any thermostatic valves or outdoor reset.  Each radiator has a unique branch off the mains and unique return to the master return.  I calculated the EDR of all the radiators in the house, and I got 75k on the main floor and 53k on the second floor.

I haven't calculated the heat load of the house, but I can if that makes a big difference.  The house is comfortable and uniformly heated, but there are two main things I want to change-

The pipes in the basement are about a foot below the ceiling.  I'd like to eventually finish the basement, so I'd like to replace everything with a manifold and Al-Pex in the homerun configuration.  I also want to replace my circulating pump, since it uses a lot of electricity. 

Without changing the boiler, does it make sense to go to a ECM Grundfos Alpha, add thermostatic valves, and seriously reduce the water volume by running everything in 3/4 or 5/8" Pex?  I'm pretty sure the boiler is oversized, so would a bypass, outdoor reset, or ??? help?

Finally, the additional complication is would any of your suggestions change if I ever want to swap in a mod/con boiler with indirect hot water?

Thanks for your advice. 


  • Fred RappuhnFred Rappuhn Member Posts: 93
    intrested in the replys

    I am very interested in your replies, I am in a very similar boat. I can tell you one thing, If you remove the large pipes and repipe you will see a change in your basement heat.  Those pipes are a major heat emitter, been there, done it.
  • IronmanIronman Member Posts: 3,420

    Why would you want to keep the old boiler? Is it gas or oil fired?
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • MichaelSMichaelS Member Posts: 8
    edited March 2013

    Becauset the current gas-fired boiler works fine, and the efficiency gain I'd get from a new boiler would never pay back the costs of a new unit.
  • SWEISWEI Member Posts: 7,356

    At 75 BTUs per square foot, that boiler is massively oversized.  Start with a heat loss calc to see what you really need.  A buffer tank (electric tank water heater is the least expensive route) and ODR could help a lot.

    How much do you spend on fuel per year, and again -- what kind of fuel is it?
  • MichaelSMichaelS Member Posts: 8
    edited March 2013

    Natural gas.  Total gas bill for last year was just under $1350, and that's before the wall, rim joist, and basement insulation.  My gas bills since then have been 10-20% lower.

    Electricity is just under $.14/kWh.

    I'll do the heat load calc this weekend...

  • IronmanIronman Member Posts: 3,420
    40% not Enough

    That's the minimum we've seen with a properly sized and installed mod/con on a gravity conversion.

    The cast iron beast will eventually go out anyway, then you'll have to upgrade But, you'll have lost the $$ you could have saved during that time.

    Don't confuse combustion efficiency with operating efficiency or system efficiency. What you have now would have done well to hit 55 - 60% operating efficiency the day it came out of the crate.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • MichaelSMichaelS Member Posts: 8

    Assuming 1k yearly cost of fuel, even if I save 50% I'm still looking at a payback time way over 10 years. I'd love to do it and probably will when I have an extra 10k, but that's not now.

    The pipe replacement is to add headroom to the basement for when I finish it. I know I can drop my electricity consumption by going to an ECM pump, so I was wondering if there were other similar measures that would pay off. I suppose things that would help me avoid short cycling would be good too.
  • IronmanIronman Member Posts: 3,420
    Short Cycling...

    May become an issue if you replace the large pipes. Now, the volume of water they hold acts as a buffer. Take that away and the boiler will definitely cycle more which will reduce efficiency and maybe balance and comfort as well.

    You'll need to get rid of the expansion tank in the attic and install a diaphragm tank and an MBR. Check the second floor rads for orifice plates and remove them if present. A manifold with flow setters is highly recommended.

    Here's a very helpful article by Dan:
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • SWEISWEI Member Posts: 7,356
    heat loss calc

    is your first step, especially now that you have done a few envelope upgrades.  Are there plans for more of those?
  • MichaelSMichaelS Member Posts: 8
    expansion tank

    The old expansion tank had been replaced by a diaphram tank sometime in the past.  I was just guessing that it used to be gravity (and maybe not steam), by the tank and the large pipes.  I'd seen that article and that led me to think that it was gravity.

    I haven't looked to see if there are restrictor plates upstairs, but those radiators get plenty warm.  There isn't a bypass on the boiler right now- just a big circulator on the return side.

    Sorry, what is a MBR?
  • MichaelSMichaelS Member Posts: 8

    Other than better air sealing in the attic and around the outside of the house when I paint this spring, no.  There are aluminum storms and I'm not replacing windows.
  • MichaelSMichaelS Member Posts: 8
    Heat loss calc

    I did the heat loss calculation, and got 65 kBtu/hr design for a design temp of 0 degrees.  No idea if this is reasonable (seems low but I have no reference point)- 2400 sq feet (40x25 with 9 and 8.25 foot ceilings), about 1 air exchange per hour, 500 sq feet of windows, r-13 in the walls and r-39 in the attic, basement walls 42" above grade and insulated to R-10...
  • SWEISWEI Member Posts: 7,356
    37 BTU/sq ft

    Sounds about right for what you you described.   If that's accurate, your current boiler is twice as big as it needs to be to heat your home on the coldest ay of the year.

    I'd probably be looking at a Lochinvar WHN-085 for that job...
  • MichaelSMichaelS Member Posts: 8

    Thanks for the suggestion, but I'm more interested in finding out if there's anything I can do to my existing system to make it run more a new pump or ODR or a bypass.
  • SWEISWEI Member Posts: 7,356
    edited March 2013
    buffer tank and ODR

    will reduce the short cycling.

    Did you use 170 BTU/sq ft for your EDR calculation?  If so, you should have measured 753 square feet, which can deliver the 65k output you need on a design day using roughly 140F water.  Any time the outdoor temp is higher, you would need cooler water to prevent overshoot.

    Adding basic ODR control to the existing boiler would not help much since the highest temperature you need is at the low limit of what can be delivered safely by a conventional boiler.

    If I were asked to upgrade your system, I would install an ODR-controlled mixing valve (Taco iSeries-R is usually the least expensive answer there) on the system side of tank-type electric water heater used as a buffer with an ECM system circ on constant circulation.  Then set the boiler aquastat to to keep the buffer tank at 150-160F.  The cost of all this will probably come to about half that of a new mod/con boiler.

    Given the age and efficiency and oversizing of your existing boiler I'd take another hard look at ROI (and probably end up recommending the mod/con.)
  • MichaelSMichaelS Member Posts: 8

    Yes, I used 170 Btu/hr EDR.  I calculated 445 sq ft EDR for the main floor and 312 sq ft EDR for the upstairs.

    Thanks for the info- makes sense.  I guess I should save up and wait for the boiler to die.  If I understand it correctly, reducing the water in the pipes by replumbing in pex would just increase the short cycling and hasten it's demise.

    As for a new ECM pump, is there anything wrong with doing this?  I think it could be carried over and used in the new system.  I'd definitely save a lot of electricity.
  • ivanatorivanator Member Posts: 39
    We're where you are, kinda

    We have an 1888 house in Minneapolis. Also rehabbing the windows. You'll tighten things up quite a bit rehabbing the windows. Our heating costs will be $4,000+ this year.

    Running pex-al-pex off a manifold to your cast iron radiators will work with any future improvements. I ran pex with a manifold for first floor rads last Fall, and plan to do the same for second and third floor this year. I did a room-by-room heat loss and concluded I only needed 1/2 inch pex-al-pex. And we have some big rooms (16x16 with 10 ft ceilings).

    We are undertaking weatherization retrofits like insulation and tightening the envelope this year, then ditching our boiler for a high efficiency unit.

    If you are seriously going to consider replacing your boiler in the future, I would find a way to make that happen sooner than later. If you wait 5 years, all that money you spent on running that old boiler for those 5 years is gone up your chimney. It could have gone toward a new boiler, offsetting some of the costs.

    I know there's only so much money to go around, and like us, you probably have many projects and you want to spread your money around a bit.

    I concluded I could spend one dollar now, or spend that

    same dollar down the road in higher heating costs - it's the same

    dollar. We plan to be here beyond the payback period, but I also

    consider it a home improvement if we were to sell ("new mechanicals!" as

    the realtors like to say).

    In Minneapolis, we are obligated to bring in an inspector when selling a house. They're tagging old boilers for inspections quite a bit and there is some liability for any company coming in to inspect the boiler. They have to fill out a form saying they inspected it, and it passed and submit it to the city.

    If you plan on flipping the house and will only be there a few years, then have you considered a new cast iron boiler? Much, much cheaper.

    Or maybe you could find someone to put in a cheaper mod-con (Munchkin?) and do the near-boiler piping, and leave you to connect your manifolds and run your pex.

    Based on my own experience, I wouldn't spend any money on your current system unless those components would also be part of any future, optimally designed system.
  • SWEISWEI Member Posts: 7,356
    edited March 2013
    when to buy, and what

    A less expensive mod/con will quite likely cost more to install, given the requirement for primary/secondary piping and two circulators.  It will come with higher maintenance costs and bigger electric bills.

    With those wonderful oversized cast-iron radiators, you can run a higher ∆T and direct pump a firetube boiler which should be condensing the entire season.  Ironman is probably right with that 40% fuel savings estimate for a properly sized, installed, and commissioned TT PST or Lochinvar WHN boiler.   Factor in historically low interest rates, a few percent per year rise in NG costs, and you may like the payback.  Borrowing money from a bank, a 401(k) or some utility program could make a lot of sense if you plan on keeping the house for awhile.

    If plan to follow this route, and not modify the piping too much, an ECM circulator may make sense at this time, since a fire-tube mod/con will not have much more HX head than the old CI boiler.  If you do this, be prepared to purge and flush several times, add water treatment and a Caleffi DirtMag to protect the new circ.
  • IronmanIronman Member Posts: 3,420

    Micro Bubble Resorber: like SpiroVent, etc.
    Bob Boan

    You can choose to do what you want, but you cannot choose the consequences.
  • JohnHenryJohnHenry Member Posts: 70
    another thing to consider

    I just went through all that on my house. Had the original 1931 coal fired boiler that had been converted to run on oil in 1941.

    I tried to sell the house a couple years back and the old boiler and asbestos wrapped gravity pipes hanging down a foot from the basement ceiling were total deal breakers. I didn't get a single offer. It's a really nice house, too. Originally built by Bill Boeing. Yes, the founder of the Boeing airplane company.

    One must remember that the number of people willing to buy a house that old in spite of it's charm is pretty low and the number of people willing to buy one with the old gravity set-up still in place is absolutely minuscule. Consider yourself one in a million.

    I'd consider it a "hedge" to change it out to a more modern system. You never know if/when you're going to have to get out from a place in a hurry. Having the old system in there can make it nearly impossible.

    Also, the modern system will just plain work better. A lot less expansion and contraction noises. Almost no temperature swings etc. For me, it was almost worth it for that alone.

    Just my 2 cents.
    The bitterness of poor quality remains long after the sweetness of low price is forgotten.
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