Air to Air Heat Exchanger

[Junkman]

The 1,250-square-foot home I am renovating will be super tight with new energy-efficient doors and windows. The walls will have 5" (R-30+) of high-density foam installed, and the attic roof and gable ends will be insulated with the same high-density foam to R60. The home is heated and cooled by 5 wall-mounted mini-splits, each with an individual thermostat. Tonight, while reading, I started thinking about the air quality in such a tight house. I think I might need an air-to-air heat exchanger, and the only place it can be installed is in the attic. Looking for suggestions for brands and how this could be accomplished economically. The upper floor has a kitchen, bathroom, and a master bedroom. The downstairs has 2 rooms, an entryway, a washer/dryer, a bathroom with a shower and toilet, and a small utility room where the well control and water tank will reside. It will also contain the propane-fired instant water heater, which has an outside vent pipe. The living room might have a ventless gas (propane-fired) fireplace insert for supplemental heat when the outside temperature drops to negative numbers. The house is located on the CT/MA border, where we get lots of cold weather during the winter months.

 

[larry4406]

I would rethink the ventless propane fireplace.

The interior of the home is the vent. Fine print in the manual usually says to open the window...

 

[Dagny]

Skip anything ventless. What refrigerant are the mini splits?

 

[PCustoms]

X3 on NO ventless, that's going to push humidity well past 60%

 

[devvar]

Check out the section on single point ventilation from Building Science Corp:

Info-611: Balanced Ventilation Systems (HRVs and ERVs) | buildingscience.com

buildingscience.com

You could run the duct from the attic to the first floor through a closet or something. You could also do something like this ceiling mounted Panasonic, could make the ducting easier

https://www.supplyhouse.com/Panasonic-FV-06VE1-Panasonic-WhisperComfort-60-Energy-Recovery-Ventilator-ERV-Wall-Ceiling-Mount-Exhaust-Fan-FV-06VE1

 

[fitter30]

Would want a direct vent fireplace. They take in combustion air and have a power vent that vents out the backside. Don't know how much heat they put into house. Ventlless fireplace or stove not made for a tight house. HRV transfers heat or ERV transfers moisture for fresh air Info on you tube and web.

 

[250]

EVR/HVR is where you need to look. Bring fresh air in and exhaust the stale air. You put the supply into the living spaces, living room, bed rooms, etc etc, and draw the old air out of the kitchen, bathrooms, laundry. And it needs to be balanced. Zehnder is the name at the top of the pile to get you started but there are others. In a tightly sealed house, combustion for heating is generally frowned upon by the green crowd, but its there, in reality. You just have to determine how the combustion unit is going to breath.

The building science corp as quality information, as does greenbuildingadvisor. If you've piling on the exterior insulation, both are worth digging into.

Undecided with Matt Ferrell on youtube has some interesting topics that would be up this alley.

 

[Junkman]

Check out the section on single point ventilation from Building Science Corp:

Info-611: Balanced Ventilation Systems (HRVs and ERVs) | buildingscience.com

buildingscience.com

You could run the duct from the attic to the first floor through a closet or something. You could also do something like this ceiling mounted Panasonic, could make the ducting easier

https://www.supplyhouse.com/Panasonic-FV-06VE1-Panasonic-WhisperComfort-60-Energy-Recovery-Ventilator-ERV-Wall-Ceiling-Mount-Exhaust-Fan-FV-06VE1

I took your advice and I ordered a Panasonic FV-06VE1. The instructions say to use insulated flexible ducting, and I have a choice of 4" or 5" and R-6 or R-8. I was thinking that it would "breath" better with the larger hoses, however, the distance to the outside wall is about 15/16 feet. Since the R value of the ducting is so low, is it worth the extra cost to go with R-8 ducts? thanks Junk

 

[250]

Are these ducts inside your thermal envelope?

 

[Junkman]

Are these ducts inside your thermal envelope?

Yes, in the attic, which is insulated with high-density spray foam on the underside of the roof and the side walls.

 

[250]

It looks like the install manual doesn't specify anything other than insulated ducting. Given that you're inside your thermal envelope I don't think it makes a difference, I doubt there will be enough of a temp delta to have condensation issues. If so you can retrofit more insulation around the piping. From a resistance standpoint, ridged piping would be better.

 

[Denwood]

I’m in a similar situation, 1800 sq/ft on 2 upper floors and a basement. Lots of retrofits to the point where air quality was a real issue as we tightened the place up. Been gathering IAQ data from all 3 floors for a few years now.

Go with 6” if you can and R8 then step down to the 5” at the unit, particularly if using flex!! Condensation will be an issue on the fresh air intake in winter, for sure.

I had the previous version of that ERV and had to replace it due to the low CFM not keeping up with co2 in our space. Nice to see they have redesigned it! I would normally advise not using a unit like this in a larger space, but it sounds like your living area is all on the top floor. Doing this again, I would dearly wish someone had provided the paragraph below!!

Be aware that the FV-06VE1 is only rated at 70% efficiency at 19 CFM which means at 50CFM it will be quite a bit worse. This means in winter you will have quite cool air dumping into your living space at 50 CFM. If you provide your lowest temps outside in winter I can provide some numbers for you. In your situation I would take a long hard look at the RenewAire Premium L which is also sold under a few other brand names. It’s far more efficient and you can add a few stale air and fresh air ducts. None of the ducting would need insulation in your conditioned space.

This is an amazing resource: https://www.hvi.org/hvi-certified-products-directory/section-iii-hrv-erv-directory-listing/

How many occupants? 50 CFM may not do it..

Does your main floor bath have an exhaust fan?

Don’t do a ventless anything, unless it’s a condensing clothes dryer