Author Topic: HRV as an Air Supply  (Read 2099 times)

Offline tmcmco

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HRV as an Air Supply
« on: December 08, 2018, 07:38:51 PM »
For a non direct vent furnace in a R-2000 home, can an HRV be used as an air-supply?

My gut is telling me no but it looks like as long as 8.6 and 8.8.1 are followed it’s ok.

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Re: HRV as an Air Supply
« Reply #1 on: December 08, 2018, 08:53:58 PM »
I think those Clauses apply to air supply assemblies with dampers or fans.  An HRV will bring in roughly the same amount of air as it exhausts and would not be considered an outdoor air supply.

There was a time when building inspectors required an HRV when a wood burning fireplace was installed but they were confusing an HRV with a make-up air unit.

These days they pass occupancies in townhouses without HRV’s simply because the principal bath fan is interlocked with the furnace fan not realising this is not providing ventilation.  There would need to be an outdoor air supply piped directly into the return air or in most cases a make up air unit to preheat the incoming air.  Without this it is circulation not ventilation.

Alot of builders will use an SB Performance Package and install a tankless water heater to avoid installing an HRV.

Offline tmcmco

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Re: HRV as an Air Supply
« Reply #2 on: December 08, 2018, 09:46:40 PM »
I think those Clauses apply to air supply assemblies with dampers or fans.  An HRV will bring in roughly the same amount of air as it exhausts and would not be considered an outdoor air supply.

There was a time when building inspectors required an HRV when a wood burning fireplace was installed but they were mistaking an HRV with a make-up air unit.

These days they pass occupancies in townhouses without HRV’s simply because the principal bath fan is interlocked with the furnace fan not realising this is not providing ventilation.  There would need to be an outdoor air supply piped directly into the return air or in most cases a make up air unit to preheat the incoming air.  Without this it is circulation not ventilation.

Alot of builders will use an SB Performance Package and install a tankless water heater to avoid installing an HRV.

That makes sense. Thanks for the reply.

What's the best way of getting this addressed? I'm thinking call TSSA directly and get it inspected. (Seems extreme but I'd rather save the owner any grief trying to get the installers back onsite.) Friend of mine just had the furnace installed, was asked to take a look.

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Re: HRV as an Air Supply
« Reply #3 on: December 09, 2018, 07:16:05 AM »
The HRV is not always running or providing an air supply to the furnace, so an outdoor air supply is required for a non direct vent furnace.  You could issue a warning tag for Clause 8.2.1.

Did this new furnace replace an older one?  If so it’s unlikely the old furnace was to Code if no outdoor air supply was installed.  I suspect the best thing to do is contact the installer before the TSSA and your friend would have to pay them to add the outdoor air supply.  The best option is to use cheaper ABS and connect the intake directly to the furnace so it becomes direct vent.

The installer may just do it for free if they did not leave the installation Code compliant.  It’s something they should have included in their original quote.

Offline Porcupinepuffer

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Re: HRV as an Air Supply
« Reply #4 on: December 09, 2018, 09:31:14 AM »
Or running a 4" insulated fresh air to the furnace. It wouldn't be as efficient as having it direct vented, but it would provide fresh air for the furnace and help if other appliances/exhausts put the house under a negative pressure.

Offline tmcmco

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Re: HRV as an Air Supply
« Reply #5 on: December 09, 2018, 12:09:26 PM »
Did this new furnace replace an older one?  If so it’s unlikely the old furnace was to Code if no outdoor air supply was installed.

Yes, this was replacing an old furnace. Mid efficiency. Which I don't get, how could they have vapour barrier and an HRV, and no outside air supply for the furnace?


I have one last question in regards to the code, want to make sure I understand it correctly:

In a non R-2000 home, it would be legal to install a category IV appliance utilizing non direct venting.

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Re: HRV as an Air Supply
« Reply #6 on: December 09, 2018, 04:36:06 PM »
Quote
In a non R-2000 home, it would be legal to install a category IV appliance utilizing non direct venting.

In a non R-2000 home you may be able to use Table 8.3 or 8.4 and depending on how much volume of air you have, in the furnace enclusure, an outdoor air supply may not be required.  Using Table 8.4 a 75,000 BTU furnace would need roughly a 38’ x 10’ room with 8’ high ceilings to have 3000 ft3 of volume and not require an outdoor air supply.

It shouldn't matter how the house is built.  If the furnace is approved as a direct vent or non direct vent, it could be installed either way.

Today's Building Code requires a furnace equipped with an ECM fan motor.  The builder package determines the AFUE.  The options are 92% to 96% AFUE high efficiency furnaces, but it doesn't matter if the furnace is direct vent or non direct vent.  Usually if you want to use the furnace during construction it would have to be direct vent as per the installation manual.  Most builder scope of work documents call for direct vent installations.