I notice that a lot of new construction standards have all kinds of very tight, thick insulation standards which is great for saving energy, but do I really care about this if I am ventilating the house?

For example, if the house is getting 4 air changes per hour, insulation doesn't really seem to matter because I am bringing in freezing cold air into the house constantly, so the amount of cold coming in through the ventilation system will be way higher the amount of cold coming through the walls/windows. So, why even worry about insulation?

I live in New England where temperatures easily get to -10 degrees F and below in the winter and up to 95-100 F in the summer.

In my current (old) house, I have forced hot water heating and no ventilation system at all, but the house is so leaky that I get air coming in through the cracks and crannies. So, lets say I am getting 2 ACH by leakage in my current house. Would that mean I am actually going to be spending twice as much heating a new house which has 4 ACH forced air ventilation?

  • 1
    Won't there be some type of heat exchanger to temper the incoming air? Sorry if that's dumb, but the concept of purposely bringing in air from outside is foreign to me.
    – JPhi1618
    Commented Oct 19, 2017 at 18:00
  • @JPhi1618 All the heat exchanger does is heat the air. If I am bringing -10F air into the house and heating it to 72F that energy has to come from somewhere. Commented Oct 19, 2017 at 18:17
  • A heat recovery ventilator (air-air heat exchanger) heats the incoming air with heat in the outgoing air. They are about 80% efficient, typically, IIRC. 4 ACH is also an absurdly high ventilation rate. But Tyler has shown a flair for the absurd, so I say build the house from breeze block and put a blast furnace in the middle, then spin constantly.
    – Ecnerwal
    Commented Oct 19, 2017 at 19:25
  • In most balanced systems the air intake and outtake are close to each other and the heat/energy exchanger heats the incoming air with the outgoing air.
    – StrongBad
    Commented Oct 19, 2017 at 19:26
  • 1
    @Ecnerwal, thanks for "breeze blocks". I never new what the name of those was.
    – JPhi1618
    Commented Oct 19, 2017 at 20:02

1 Answer 1


As is typical of your past questions, you are being hyperbolic and absurd.

ASHRHE suggests a ventilation rate of 40 to 70 CFM - if we took 70 CFM and 4 air changes per hour, your house would be a 10 foot cube, roughly. As far as I recall past mention of your purported house, it will be much, much, much larger than that.

As such, the ACH (which would still be at most 70 per that standard) will be far below 4. And the surface area of poorly insulated or uninsulated building to enclose that area will be large, and losing a metric-butt-ton® of heat as a result.

I've run the numbers in past answers. Are BTU's only calculated using square feet?

Dropping them into my shop's spreadsheet, 70 CFM is 0.1736 ACH and amounts to 6381 BTU/hr at design temperature (-20°F). It will be a shade less if yours is only -10°F The walls (R33 SIPs) account for 6709 BTU/hr at design temperature. If you made the walls crappy R11 they'd burn 20128 BTU/Hr instead. I don't even need to get into the ceiling, floor, doors, or windows (all additional heat flows) to make fairly clear that even without a HRV, yes, insulation matters. Of course, if you added an HRV you could shave off 5104 btu/hr at my design temperature, and that's something I'm certainly considering doing.

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