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Community and Q&A

Keep The Cast Iron Boiler, or Install/Wait for Better Tech?

Rory | Posted in Energy Efficiency and Durability on

Hi all,
I’m new here and new to green building. I’m currently trying to find the best balance (probably like most of us) between greening my home and cost effectiveness, at the same time as learning what goes into making a home a home. A lot of the language is new to me, so feel free to ask me to clarify.

I just bought a 120 year old house in central Ontario, Canada. The house is 2500 sq ft, and heated with radiant heating from a 20 year old cast iron boiler. 107000 BTU, 82% AFUE. Haven’t had a winter in this house yet, but seems like at least 2/3rds of the house is insulated, and my guess is renovations happened here in 98. Some walls facing the outside still have the original plaster on them, so interested in seeing how they fare during the winter. Windows are 100 yrs old and new, high efficiency ones will be installed in January.

There’s a duct system installed, but it’s AC only and starts in the attic and goes down to the main floor. I checked if a cold air heat pump would work in my home, but numerous HVAC sales guys highly recommended I didn’t use for a heat pump system for a number of reasons.

My main question is then: do I keep the cast iron boiler and wait for better tech down the road, like hydrogen boilers, an air to water boilers, or some better and different technology to heat/cool my home? Or is it worth my while to switch to a condensing boiler right away? I’m noticing that Europe is way ahead of us, but Canada really lags in terms of cleaner and cheaper to run technology.


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  1. paul_wiedefeld | | #1

    Why exactly were heat pumps discouraged? A heat pump is the green option. A condensing boiler is only marginally greener than what you already have.

    The existing system is hot water and what kind of emitters?

    1. Rory | | #2

      Good to know a condensing boiler has only marginal benefits compared to what I've got. The emitters are mostly original cast iron rads on the first and second floor. Our kitchen has in floor rads, and the 3rd floor attic master bedroom has a newer baseboard rad.

      An air to water heat pump was discouraged by two HVAC techs because I was told that they don't yet exist in Canada, and I can't find much info on them either. But the HVAC tech said they might be showing up in a couple of years.

      An air source heat pump is discouraged because my duct system, which is only AC, is set up in a crawlspace around an attic cathedral ceiling bedroom (so horizontal AHU setup, if that makes a difference). That crawlspace is mostly insulated towards the roof and the bedroom, no more than R20-30 with white and pink fibreglass (I can share pics if that helps) and isn't heated. As well, the registers are all ceiling mounted (except for the master) and the ground floor has 12 foot ceilings. They said that the heat won't penetrate enough to the ground floor and would avoid the basement altogether. My wife refuses to have ductless heat pumps installed.

      I'd personally prefer a heat pump. They're affordable for me through government grants. But the setup is really focused around gas in this house. I want to change that, but need to manage cost as well.

      1. paul_wiedefeld | | #3

        Ha surprisingly, I think several of the air-to-water manufacturers are based in Canada. They are definitely less common though.

        The cheapest solution would be to replace the AC with a heat pump whenever the time comes, which might not cost a penny more than replacing the AC with another AC-only unit. Air-to-water would work as well - you may have to keep the boiler in a supporting role, but not a big deal.

        Use this to find the heat loss: You might be able to get the previous usage or wait a few months and get November and December's gas usage. You'll need the heat loss to reassure contractors the heat pump will be big enough to cover the load.

        1. DC_Contrarian | | #7

          Here's why I don't think a heat pump is practical. I don't know where in Ontario the OP is located, and I don't have Canadian data handy, but let's take Buffalo, NY, as someplace nearby. According to my chart the heating design temperature is 7F and the cooling design temperature is 84F.

          Let's say the ductwork is sized to keep the interior at 74F on the design day, or 10F below ambient. Let's also say the cooling air is at 49F, or 25F below interior. To keep the interior at 70F with the same airflow when it's 7F outside -- 63F above ambient -- you'd need air at 157F above interior, or 227F. That might present comfort issues.

          If the ducts were properly sized for cooling only they're way undersized for heating in this climate.

          1. Rory | | #9

            Fully agree with you, DC. Buffalo is a good example of where I am. I'm just 4 hours north of there, but we have similar climates. A heat pump could work in our area, but it gets damn cold, averaging 7F like you said.

            If our duct system was designed from the ground up, from our basement to the attic, a heat pump would be perfect. But whoever renovated this house, and those afterwards, didn't think that over and kept the house designed around hydronic heating.

      2. DC_Contrarian | | #8

        Arctic heat pumps are based in Manitoba:

        1. Rory | | #10

          They look great. Wish they had air-to-water heat pumps that went up to 100,000 BTU though. But I need a hybrid water heater and they're priced way better than many others.

          1. paul_wiedefeld | | #12

            You can team them together to get higher capacities. But first track the gas usage and figure out the real heat loss.

  2. steve41 | | #4


    We were in the same boat ~8 years ago when we bought a ~120yr old house, zone 6. The old oil boiler seemed to be on it's last legs and I was planning to rip everything out and do it "right". Ultimately, we decided to just live in the house for a few years to see what we like and what we don't like about the HVAC, and everything else. Interestingly what we were originally planning, and what we ended up deciding to do, were drastically different. With a little time and more familiarity with the house, and a better understanding of how we live in it, our plans evolved. So that would be my suggestion: Live in your new house for a year or two.

    Also, this delay will provide you with research time. Best of luck.

    1. Rory | | #6

      So funny you mention this. My wife just said the same thing to me last night as she tried to slow me down from all my 'obsessive' research.
      It helps to hear it again. Besides getting the windows done cause they're painted shut and very old, and maybe some insulation and other small tweaks, I'm starting to think you and my wife are right.

  3. walta100 | | #5

    From a dollars and cents point of view replacing the boiler that is likely to remain serviceable for another 20 years is a very poor choice as you are unlikely to live long enough to recover the installation cost in fuel saving. Note this same argument applies the window replacement plan likely another poor choice in dollar terms.

    I tend to agree that an air to air heat pump with equipment and ductwork in the attic is also a poor option and that air to water HPs are finicky over priced unicorns and best avoided until they become mainstream.

    Note hydrogen much like electricity is not a fuel but more of an intermediate energy transfer device. There are no hydrogen fields, mines or wells virtually all of it is produced with massive amounts of other types energy being expended.

    Form my point of view the most ungreen thing someone can do is to discard still useable items on a whim well before it is necessary.

    I say spend your efforts on the unsexy work of sealing where the air is leaking in and out of your house and adding insulation. Note these two items are not without risk in the heat and air leaks may well be drying out water that has been leaking since the building was new and mold and rot could become a problem.

    Has the house been blower door tested?


    1. Rory | | #11

      Thanks for the info, Walta. I've been convinced by you, and others, that removing that boiler for anything less than a heat pump or more efficient device makes no sense. Really glad I came across this community.

      I've had a chance to dive deeper and found Air-To-Water HP from Noraire and MBtek, but I'll see if anyone knows how to install systems like those. Otherwise, I'll at the minimum get a heat pump water heater to replace my 20 yr old gas water heater.

      Our house has been blower tested and our 100 year old, painted shut windows failed, as did a number of other spots. Doesn't seem like the old owners did much regarding air sealing, so i'll need to take care of that before winter hits and it should hopefully help a lot.

      For insulation, the attic has R20-30 (pink fibreglass), so I'll need to check if it's worth improving with spray foam insulation.

  4. walta100 | | #13

    What ACH50 number did the blower door test give you?

    I think a blower door test is useful to understand how leaky your house is. No doubt a 120-year-old house is very leaky You need to fix the leaks the blower helps you identify and retest hopefully you will get a lower number If you can get a number under 2.5 ACH50 that would be very impressive.

    This is called blower door directed air sealing the work is not complex it is time consuming and sometimes frustrating in that you fix several leaks and the number can remain unchanged. If you are willing to do the work it is only a matter of caulking up the gaps. If you tape a box fan into any window and use the smoke from incense sticks to find the leaks.

    It seems lots of people see the use of spray foam as the mark of quality work. I don’t I see large amounts of spray foam at the mark of laziness by someone with little regard for the cost. Yes, sometimes it is the only real option. Spray foaming the roof and conditioning the attic is only a marginal improvement over the truly bad idea of HVAC equipment in an attic. Seems like a creative person could avoided the bad idea somehow.

    In terms of dollars, it is very hard to justify an existing R30 attic as the amount of fuel saved is pretty small. If you are closer to R20 it may become viable if the plan is to stay for many years.


    1. Rory | | #15

      Not sure if this is ACH50, but my report tells me air leakage at 50 pascals is 8.4 air changes/hour. Sounds like my house is swiss cheese.

      Thanks for the tip. I'll probably be spending a few weekends caulking and weather stripping everywhere. My basement is fully unfinished, so I wouldn't be surprised if that's a big portion of the problem, and I'll need to air seal the basement from the rest of the house.

      I appreciate the advice on my attic. I'll need to check in on how thick the fiberglass is up there.

      1. DC_Contrarian | | #17

        ACH50 is air changes per hour at 50 pascal, so that's exactly the number you want to be looking at. I'd say 8.4 isn't terrible but lots of room for improvement.

        Generally you want the basement to be part of the conditioned space of the house even if it isn't heated. So what you want to be sealing is the walls of the basement, not the space between the basement and the rest of the house.

  5. iainb | | #14

    I’ve looked at the options for switching to an air to water heat pump for my 1938 house, zone 5, MA. What I keep running up against is that they’re inevitably a lower water temperature, by a lot, with much lower radiator output as a result. Daikin Altherma had a high temp version, so it actually runs at 70-80c, but they discontinued it in North America.

    Air to water heat pumps just don’t seem to be drop in replacements yet.

    I’m doing what another post has suggested. Find my fuel usage and figure out tea BTU usage (I had to make some guesses), air seal, improve insulation, and take another look at fuel usage.

    I’m personally hoping to not put in a replacement boiler and hope to get better tech….but I’m thinking I may need a bigger overhaul of the system and switch away from hydronic heat.

    If the objection to minisplits is the indoor unit (hey, it’s mine too), do you have the space to build short ducted minisplits into soffits?

    1. Rory | | #16

      That's a good point. I've been looking at the Apollo from MBtek and they go up to 72k BTU which still wouldn't match the 107K BTW cast iron I have in my basement.

      Short, ducted minisplits looks like a really fascinating option and I'll keep it in mind. Like you, I'm taking the advice of many people here and air sealing, improving insulation and then take another look at my fuel usage. Hopefully newer tech will come down the road next year or the year after to take advantage of.

  6. joshdurston | | #18

    Agree with the keep the boiler sentiment. Depending on your floorplan, you could put a ductless in that would cover the shoulder seasons on your main living area. I have an older oversized boiler, but am able to minimize the runtime with a wall mounted cold climate minisplit that covers my living room/kitchen area. If it's above -5C it seems to heat most of the house adequately, an lower, and a point source heat pump doesn't seem to cut it any more for distribution. There is a lot of the winter here in Ontario that isn't that cold so the heat pump offsets a lot of the load on the boiler.

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