Heat recovery ventilator on rocket stove exhaust

Any type of stove uses inside air for combustion and creates negative pressure in the home where outside air will seep in.
Passive house principle requires airtight home and heat recovery ventilator to heat the incoming air with outgoing air.
Rocket stove mass heater exhaust temp is low enough to try to use it with heat recovery ventilator to use the remaining heat to warm the incoming air so cold air doesn't have to seep in.
Did anyone try this idea?

Personally, I'd think using a heat exchanger in the exhaust gases of a rocket heater would lead to problems. When started up, the heater being cold, there will be some soot deposition in the exhaust system. Not a lot, but enough to clog up the heat exchanger slowly over a couple of months time. Which in turn would lead to a restricted air provision and incomplete combustion.

It would be much better to separate the exhaust system and the combustion air system completely. After much experimentation, I found out there's a way to avoid cold draft entirely. In what we (in the Netherlands) are calling a balanced ventilation unit there are two ventilators. One that extract air out of the building and one that blows air in. Between those two streams there's the heat recovery unit or heat exchanger. In our ventilation unit there are three presets possibilities. All three could be tuned to balance the incoming and outgoing air volumes independently. One of those presets in our unit is now tuned in such a way the extracting fan is running 5% slower than the one that blows air in. Which (in our situation ) is just enough to compensate for the chimney draft.

Result: when the heater is about to be fired up, I select preset #3, then load the heater and lite it.
Works 100 times out of 100 for us. Stone cold heater, first fire of the season, it doesn't make a difference. Never had any problem again with a recalcitrant heater, smoke in the room and so on. It might be that you have to carefully try what the minimum requirement would be. We started with 15% speed difference which was grossly overdone. We even could feel it when we opened a door, the overpressure in the house was far too great. Now is has been 5% for the past 7 years, never changed it since then.

Peter, did you have door blower test performed on your house? Most houses I’ve lived in have so many leaks there’s no way a small ventilation fan would pressurize the house. But our next house is like to to perform better.

Jeremy Baker wrote:Peter, did you have door blower test performed on your house? Most houses I’ve lived in have so many leaks there’s no way a small ventilation fan would pressurize the house. But our next house is like to to perform better.

Yes, our house has passed a blowerdoor test, with flying colours I might add. It's a passive house by the way, built in 2013/2014.

Peter,

If you make 5% volume difference in your fan, how much different is the incoming air temperature vs when the both fans are running equally.

Erdenebileg Purevsuren wrote:If you make 5% volume difference in your fan, how much different is the incoming air temperature vs when the both fans are running equally.

Tricky question, I never measured or noticed any difference. In case there is a difference, this should be minimal since there's no noticeable draft in the direction of the heater while it is running. And I should know, since I love fire and more often than not I tend to sit in front of the heater looking at the raging flames. Even right under the inlet openings in the room there's no cooler draft, at all. Due to the 94% efficiency of the exchanger I'd think.

That's why I think this 5% out-of-balance solution is very close to ideal.