This is from a typical North Western European housing perspective where most (older) buildings will not have forced air/AC/heat pumps etc. for various reasons, and most houses are only heated using gas powered central heating with water based radiators for transport. This means if you want fresh air in winter, you're opening a window and wasting energy in the air that was heated.

I understand the workings of forced air-to-air heat exchangers and how they can warm or cool fresh air coming in and how that could improve the energy loss situation. My question is, is it that much better than just forcing fresh air in to mingle with the stale air and having the over-pressure leak out, perhaps at the opposite end of a room or low to the ground where it is colder?

Of course I understand that you will lose some efficiency over a heat exchanger, as you will be leaking a mix of air containing also a lot of stale energy out that has not properly transferred energy. But is it that much worse considering the added complexity of a heat exchanger? Any other downsides/advantages I should be aware of?

  • Yes, run the air inlet 2m below ground to cool warmer air in summer and warm it in winter all for free after installation ( which can also be cheap with planning).
    – Solar Mike
    Feb 26, 2021 at 17:08
  • Hey @Solar, I'm not sure how that answers my question. Are you saying a heat exchanger is definitely considerably better? If so, why is that exactly? Feb 26, 2021 at 17:11
  • What do you define as “heat exchange”? Opening the window is allowing heat exchange. The pipe underground is allowing heat exchange so it is a “heat exchanger”. Or do you mean a device that has to be plugged in to use electricity?
    – Solar Mike
    Feb 26, 2021 at 17:16
  • The heat exchanger will cost more up front. But the outside air requires less heat or cooling depending on the season so power bills are reduced this is the difference over the lifetime of the exchanger it should save $ but because of the higher up front cost it takes time to pay off the investment.
    – Ed Beal
    Feb 26, 2021 at 17:16
  • I just tried to give you another option - been working fine in the house we built and saves energy...
    – Solar Mike
    Feb 26, 2021 at 17:17

2 Answers 2


This is a simple question requiring a complex answer...!

What you are asking is the cost-benefit tradeoff of installing a heat exchanger. How much will you save on heating costs, vs what does it cost to purchase and operate the exchanger. And you wish to compare that to forced air ventilation.

Factors to consider:

  • Required or desired ventilation rate, usu. depends on occupancy and your tolerance to flatulence
  • Number of heating degree days, from local climatological data
  • Heat exchanger efficiency, e.g. 60-80%, or 0% for ventilation without exchanger
  • Electricity consumed by exchanger, including its fan and defroster
  • Cost of heating, based on your local price of electrical or hydrocarbon energy
  • Purchase cost for the heat exchanger sized appropriately for your dwelling

This linked article shows a pay-back time of 5-years, but of course, it all depends on your parameters. The data in these calculations use imperial units, but it's a good example. You'll find similar calculations elsewhere, and I wouldn't be surprised if your local energy supplier has some detailed data, considering the cost of energy and your climate (Belgium? Netherlands?)


Personally I have found that in mild climates (North West Europe, Western Canada / North Western USA) the heat loss due to cracked-open windows or natural ventilation pales in comparison to the house's heat lost through building envelope cracks & radiation losses. The heat exchanger makes much more sense in areas with long winters down to -10C ... -20C.

One reason is the obvious temperature of the taken-in air, but the other is the local building code for insulation. Milder climate regions often have looser insulation requirements, and so the total energy loss is less impacted by ventilation.

  • Good guess on the country, Belgium indeed. Feb 26, 2021 at 17:55
  • Haha yes, the "uyck" hinted at that, "uik" for your northern neighbours, but who knows who moved when.
    – P2000
    Feb 26, 2021 at 17:57
  • Looking at the example calculations indeed really indicates why things are the way they are and these recovery systems are not so popular here(at least in pre-existing housing). Even in a colder climate the savings are not huge. I suppose it makes sense as regulations get stricter and when doing a big renovation or new construction. Feb 26, 2021 at 18:05

In my son's new build, he did a lot of research on HRV bc his is a hyper energy efficient new home. He selected Lunos modules (made in Germany, I believe). The American source is linked below. They are pretty pricey! I know this borders on a product recommendation, but just wanted to share what he found. I installed them.

They have 3 speeds and 2 modes of operation. In HRV mode, they cycle every 70 seconds between pulling in air and removing it. They accomplish the HRV via a heat absorbing matrix that the air goes thru. They are paired so one is pulling air in and the other is removing it, so as to avoid a pressure differential in the house. Then after 70 seconds they reverse rolls to recapture the heat from the HRV medium.

Best placement per pair are as far away as possible. They are super quiet. They are powered by low voltage cable (T-stat cable) from the control box which consists of a transformer and a mode selector. I think they draw about 5-7 watts each!

He and his wife & kids have been in the house for a few months now, his electric bill is very very low (did a mini-split system) and he really likes how it turned out.


  • This is a really interesting approach to the problem... In a sense this sort of combines forced air with an exchanger that kind of acts as a 'battery' or energy storage of sorts. Feb 26, 2021 at 17:54

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