2nd furnace for basement unit?

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Posted by: from Pickering
6/16/2021 at 1:27:26 PM

I'm in Ontario and looking into converting my basement into an income suite. I found this page ( that goes into the general regulations for building a legal unit.

Halfway down the page is this little nugget: "While the Building Code allows one furnace to heat an entire house including the second unit, you might want to consider installing a second furnace and air ducts when adding a second unit. Sharing one furnace and air ducts between two units may mean cooking smells, recreational smoke and other odours, as well as noise, may transfer from one unit to the other. Having one thermostat controlling the temperature of both units may also become an issue for residents of both units."

Does anyone ever actually do this in a basement conversion? I am finding it very difficult to find online many references to even consideration of this as an idea (but perhaps my Google-fu is rusty). If so, are there HVAC units that are physically designed to be installed side-by-side for space efficiency?

If not, what is the "typical" solution? Zoned HVAC (and accept travelling smells)? Furnace only for the main level and electric baseboard heat in the basement?

Thanks in advance.

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Date/Time6/21/2021 at 3:07:29 PM

Great question!

Ok let me dive into this.

Most people do NOT provide dual furnaces. The cost is exorbitant and as you mentioned, spacing becomes a big issue if you have a smaller mechanical room and ceiling height issues to run new ductwork.

What typically happens is the existing ductwork is fitted with an automatic fire damper (fire rating rules are EXTREAMLY important in secondary dwelling units) that allows you to include heating into your rent, bills stay in your name but you charge for anticipated heating costs in your rent being charged, much like domestic water. You cannot split bills if you go this route, and have your tenant on the hook for for all utilities. Smells will travel between units but that is a very common occurrence in basement and main floor units especially if they are smokers. Your tenant will not have access to a thermostat in this case and you will also have to keep heating limits to legal minimums for all seasons for tenants otherwise you could get in some trouble with the tenant bureau.

One solution is a heat pump and/or baseboard heaters. This will provide a secondary heating source that you can charge your new tenant with and have that under their name so they are liable for utilities. This also assumes you have a secondary electrical panel and meter to charge them hydro.

Otherwise, have a completely inclusive rent agreement, keep bills in your name, charge appropriate rent and make sure you follow heating regulations.

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Darren in Pickering
Date/Time6/23/2021 at 12:10:13 AM


Thanks for the reply. I'm looking into heat pumps for the first time, and I think I get the idea. You're saying that each room in the basement suite gets an indoor unit that mounts on the wall, and they all "share" an outdoor unit for heat exchange. The units function as A/C in the summer and heat in the winter (although baseboards may still be required in very cold weather). Please correct me if I'm misunderstanding.

What is interesting at this point is that the existing furnace and central A/C are also in need of replacement. I am also going to gut the entire basement to renovate for the basement suite, including the existing ductwork because it is too low. In your opinion, should I consider just going with heat pump units for the entire house (ground floor *and* basement), and just scrap the central HVAC and ductwork entirely? Does this make sense?

Thanks for your expertise.

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Date/Time7/3/2021 at 10:07:02 PM

Here in Alberta code states you must have "a separate system" or also allows you to install electric heating (ie: baseboard) and a HRV unit. The HRV is mandatory. Only other option is a new furnace, can't see any province allowing any use of an existing unit as sole source of air and heat.

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Darren in Pickering
Date/Time7/3/2021 at 10:32:33 PM

Well according to the linked article from my original post (and the section of text that I quoted), it *IS* allowed in Ontario, whether you think it should be or not. Rest assured I don't want to, but it can be done legally. I'm just looking for how people actually implement this in their own projects.

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