How to deal with airflow of air heat pumps?

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Posted by: from Vernon
2/9/2020 at 2:03:24 AM

I'm looking at a new home build.

My area of BC averages less than 20 days a year less than -15c, so heating cost of an air source heat pump is about the same as a HE propane furnace.

An ASHP setup is would be cheaper than a Propane furnace+ducting+ducted air conditioner.

It would save a good chunk of change, and be great for sound transfer if I wouldn't need any duct work at all.

How is air flow in a home dealt with if its heated solely by air source heat pumps?

If you only have a single unit on each floor, is there any way to heat side rooms sort-of evenly?

Do you still need ducts for any reason in a new home build?

Thanks a lot!

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Date/Time2/9/2020 at 4:38:17 PM

The building code requires dwellings have a minimum of 1/3 air changes/hour of outdoor air for mechanical ventilation so it's kind of difficult to avoid having air ducts unless you provide a separate unit delivering air to each room (like some motels). Fresh air needs to be supplied to each bedroom and principle living area; kitchens and bathrooms can rely on exhaust only. In apartment buildings with radiant heat they are able to get away with a combination of corridor pressurization (which provides 100% outdoor air) in conjunction with bathroom and kitchen exhausts. Newly introduced energy codes have created many new energy efficiency rules including mechanical systems and encouraging the use of HRV's.

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Kevin in Vernon
Date/Time2/9/2020 at 8:31:46 PM

Is the code ACH for the home, or does it need to be per actual room?

I have planned to do an ERV/HRV for fresh air.


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Date/Time2/9/2020 at 9:22:33 PM

Hi Kevin

So for new builds there are many different options.

If your going with a ductlees heat pump you can do up to 4 indoor units to one out door. Make sure its has the inverted technology Hybrid min seer rating of 22. They can produce heat at 100% down to -17c outside temp below that they efficiency starts to drop.

Vernon can get lots of snow so be sure to place the out door unit above snow level.

A couple options for air exchange thruout the house by installing a HRV heat recovery ventilation systems they supply fresh air into the house can exhaust your bath rooms have at least one 6" round insulated flex duct sulpplied to each room. Depending on size of the house you need approx 1000cfm to 3000cfm.

Or cheapest way to install passive fresh air vents through out the house make sure you kitchen and bath room exhaust to outside that will give you some air exchange.

Full ducted gas furnace with a/c is going to be costly just you ducting probably around $8k to $12k depending on the size and layout of the house.

Hope i that will help you.


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Kevin in Vernon
Date/Time2/9/2020 at 9:38:44 PM

Thanks a lot Nick! That's very helpful.

I spent the last summer re-doing the wood furnace duct system in my parents house, and I hate absolutely everything about it.

3500sq ft, 1.5 stories. LOTS of single pane windows, 2x6 walls, 12' and 22' ceiling.

They put in 2 15k btu Mitsubishi units, and they only start the wood furnace when they need to burn paper. They get surprisingly even heat too.

If I can get away without any ducts it would be amazing.

I wanted to hook the erv electrical into the kitchen and bathroom exhausts so that it turns on whenever they get used.

I'm looking at a 30x40' build, ICF basement, two more stories on top.

If each floor is 1200 sq ft, would a single wall unit for the ASHP circulate enough heat to keep it a reasonably even temperature?

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