Replies

1. Expert Member
   Akos | Jun 08, 2022 11:44am | #1

   When it comes to heat or cooling houses don't have air flow requirements they have BTU. The airflow is there to deliver the required heat and that is about it.

   The air flow issue is a hold over from old days with leaky houses. You wanted "adequate" air flow for good mixing to even out room temperature. This is one of the reasons you see larger than required furnaces in a lot of houses which ironically makes them less comfortable as they short cycle.

   Pick the heat pump that covers your load and don't worry about the air flow. The air flow is an output from the furnace selection and it is only used for designing your ducting and registers. It should not be an input for picking a heat pump.

   With a 3 story structure make sure to design in a large return near the ceiling on the third floor. Without this you'll get a lot more stratification and cooling suffers. This is a big duct and takes up space but a must for a new build.

   P.S. Most cold climate heat pumps deliver well above their nameplate rating even down to -15C. Check that actual max output of the unit you are looking to select, some 1 ton units deliver above 1.5 tons of heat. This a good resource for comparing units:

   https://ashp.neep.org/#!/product_list/

1. 
   abaerlo | Jun 08, 2022 01:15pm | #2

   Ok, great. Thanks for your help!

2. 
   walta100 | Jun 08, 2022 05:01pm | #3

   With 3 stories the challenge will be keeping all the floors at the same temperature as the warmest air will want to rise to the top and the coldest air will want to get to the bottom.

   You may want to consider mutable systems or zoning.

   Consider selecting the smaller heat pump and expecting the resistant backup heat to run a handful of hours a year. The smaller unit will remove more humidity when cooling.

   Walta

1. 
   abaerlo | Jun 09, 2022 08:32am | #4

   Yes, they've recommended three zones, one per floor. Maybe these could just be manual dampers? Thanks for your feedback!

3. 
   walta100 | Jun 10, 2022 06:34pm | #5

   I think manual dampers will work if you are ok with having several degrees of temperature variation between the different floors at times.

   Walta

4. 
   norm_farwell | Jun 11, 2022 08:04am | #6

   I’d consider two ductless heads, one on the first floor sized to handle the heating load and one on the 3rd floor sized for cooling. Assuming you have a well designed mechanical ventilation system and PH level insulation and air tightness, those btus will get distributed and you won’t have comfort issues.

1. Expert Member
   Akos | Jun 11, 2022 08:40pm | #7

   This would work for heating especially if you have a post heater on the ERV. If you are in a place with a lot of cooling, this won't be great if you ever want to sleep with closed doors.

   I think for a new build, go for ducts. Bit more work but better air distribution plus less maintaince. It is much easier to change an air filter once in a while than to clean the coil and blower wheel on a wall mount.

2. 
   abaerlo | Jun 13, 2022 08:30am | #8

   This was proposed as an option but it was suggested ducts would likely be more comfortable (and require less maintenance). We do plan on having a separate, ducted ventilation system, though.