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Thread: Furnace Replacement Question - Size Decision for Potential Secondary Suite

  1. #1
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    Furnace Replacement Question - Size Decision for Potential Secondary Suite

    I have a 1200 SQFT home built in 1978 (in Edomonton, AB, Canada) with a basement and main floor. Current furnace is servicing basement and main floor, but is not operational (several problems, holes in heat exchanger, inducer motor seized, etc). I could replace the inducer motor and maybe get another year or so out of it, but wanted to consider replacement first.

    I have had 2 quotes on replacement. The two contractors have recommended a 70 and 80 BTU furnace as the size for the entire house, respectively.

    However I have a unique situation, which I've been expressing to the contractors, and don't seem to get a straight answer to a solution. The situation: the basement is currently unfinished. I intend to finish it into a secondary suite next Spring. In my town, this requires separate HVAC for main floor and the suite - either two furnaces, or furnace serving one and baseboard heaters + HRV serving other. I haven't decided which of those options I will do, but it will likely be baseboard+HRV.

    Anyways, I want to know if it is possible to replace the furnace now, while still accomodating what I will need for the suite down the road.

    The first contractor (who recommended 70 BTU for whole house) recomended that if I did two furnaces, each would be 45 BTU. He didn't do any formal calulations however.

    The other contractor said that as long as I do two-stage, it doesn't matter if I replace current furnace with a 80 BTU, and then remove basement venting in Spring and have it just serving upstairs. This seems fishy - wouldn't this be oversized then?? It is ironic to me because the second contractor did a very detailed calc, measured windows, wood vs insulated doors, attic insulation, to come up with 80 BTU. But then when considering removing venting to the enitre basement as I would be doing, he didn't seem to be concerned that that would change the calculation???

    Common sense tells me that I should just do the right size furnace for the main floor and that this wouldn't be the same as if I was doing the whole house. But I am wondering if anyone here can provide further clarification on this, or on what else I should be asking the contractors (two more coming for quotes next week)?

    Additionally, if I have a smaller BTU furnace - should/can I leave the venting to the basement for the winter, or should it be capped now (ie. would I run the risk of undersizing the furnace, and would that matter if its only for one winter season). Capping also seems potentially problematic as the basmenet would be colder, and I have pipes down there - although maybe as long as the furnace is going it wouldn;t get below freezing temp. I'm not sure.

    Thanks for any advice in advance!

    Also can anyone point me to comparisons between brands, specifically Lennox vs. Carrier vs. Amana/Goodman? I'm looking at higher end furnaces, 96-98% efficiency. Cheers.

  2. #2
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    I have a 1200 SQFT home built in 1978 (in Edomonton, AB, Canada) with a basement and main floor. Current furnace is servicing basement and main floor, but is not operational (several problems, holes in heat exchanger, inducer motor seized, etc). I could replace the inducer motor and maybe get another year or so out of it, but wanted to consider replacement first.

    Replace the inducer, but keep the holes in the HX, and run another year?

    Those brands mentioned have tier levels, usually good, better, best. Parts come from all over the world. At best the manufacturers may make the heat exchanger and painted sheetmetal box. Possibly a tad more, like burner tubes and header assembly, pretty much all else is farmed out. Gas valve, limits, blower motor, inducer motor etc. etc.

    Not to much more to add to your other questions..

  3. #3
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    I see. Yes looking at best between brands. Seems to me, at surface level, Amana makes the best exchanger which is why it has lifetime full replacement warranty?

    Yes I mean I would like to replace it, but I'm not going to if I can't get a confident answer from anybody as to what furnace I need to accommodate the changes I plan to make. Will just have to wait and replace it all with the two new systems at the same time in the spring.

    Fix on the heat exchanger is quoted at $3000, absolutely no point doing that. Don't even think the current furnace is worth that much for the unit.

  4. #4
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    The name of the installers are more important then the names on the box's.

    I agree a Separate system for the basement is needed.

    Without measurements of the building and ducts there only guessing

    http://efficientcomfort.net/assets/d...ty_Control.pdf
    http://efficientcomfort.net/assets/d...ent_Sizing.pdf
    http://efficientcomfort.net/assets/d...s_Properly.pdf
    http://efficientcomfort.net/assets/d...ign_Issues.pdf

    Not a fan of or an endorsement of Angies List but a must read:
    https://www.angieslist.com/articles/...vac-brands.htm

  5. #5
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    I see. Yes looking at best between brands. Seems to me, at surface level, Amana makes the best exchanger which is why it has lifetime full replacement warranty?

    Amana has the best manufacturers warranty out there not necessarily the best HX to offer that warranty. It probably compatible with others if comparing to others, some brands offer stainless steel as one section and aluminized steel as the other sections, while other brands model offer both sections in SS. Chances you wanting a 96-98 % those brands models will come with SS HX. Thinking the way the system is installed has a play on the HX life expectancy, things like over firing, temperature rise across HX not to manufacturers specifications and what not. While others give a new HX if ever fails to original owner, ( once registered ) Daikin gives new furnaces on many of their models once registered.

  6. #6
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    Do not equate warranty with quality. Warranty is a selling tool, little more. If you look at the details of the warranty most are only good for the original owner. Most people, in the US anyway live in a house for 7 years on average. So how many 15 year old HX's do you think they replace?

    As for equipment size on your furnace the main floor will take much more heat than the basement. You are putting your dealer in a no win situation. if they size it for the future and you never convert the basement he is wrong, if he sizes for conversion and you don't he is wrong. I always tell home owners I have to size for what you have now because you may never make the change you are talking for what ever reason. Either bite the bullet and do the changes to the basement and make the heating proper for those changes or leave it as is and size for what you have. Dealers can not see the future so don't make them try.

  7. #7
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    Conventional for the home. Ductless for the basement.

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