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Community and Q&A

Ventilation in old house that will soon get new heating-cooling system

GWVM | Posted in Mechanicals on

I am a homeowner interested in ventilation and air quality, and I’m hoping for objective feedback on my situation (the HVAC companies have been helpful, but I’m skeptical of some of the air-quality machines they’ve proposed).

I have a leaky 1920s home (four people, 2,000 sq ft including basement and three bedrooms, 2×6 exterior walls) in the Pacific Northwest on the water (comparatively mild winters and summers, humid), if that information helps.

For heating and cooling, I’m leaning towards a ductless minisplit system, although I might go with a hybrid heat-pump/gas furnace connected to ducts.

There are a few reasons why am I interested in ventilation despite having a leaky house. An IAQ consultant recommended ventilation to deal with accumulation of CO2 that was showing up in his air-quality test of my house. I’ve also gotten feedback from other family members that the air in the house is a little stuffy. And some family members are susceptible to respiratory infections, and I am hoping that more fresh air might help with that. So ventilation seems like a good way to make the air fresher and potentially increase air quality without buying hyped-up, potentially harmful air scrubbers and the like.

So for ventilation, I know one option is an exhaust-only system with a WhisperGreen fan set on 30CFM in each of the two bathrooms (one on main floor, one in basement). But the house doesn’t have an open floor plan. More importantly, I don’t love the idea of creating pressure that would draw even more air through the house’s random cracks (and whatever humidity, mold spores, dust, etc. that would be brought through those openings) or up through the cracks in the house’s foundation/slab (house is located slightly uphill and 1,000 feet away from a former landfill). My preference is to have a bit more control over the source of the supply air, acknowledging that the house is already taking in some outside air through the house’s random cracks.

If I go with a ductless system, I’m considering spot ERV/HRVs, such as Lunos, TwinFresh Comfo, or Panasonic WhisperComfort (according to Panasonic’s recommended zones map, I’m in Zone A and could use this unit throughout the year). Depending on budget, I’m envisioning one each in the bedrooms, one in the basement, and one on the main floor, for five total. I understand an option might be passive air inlets, acknowledging that at a 2000 Vermont study raised questions about such inlets’ effectiveness. For ductless fresh-air supply, I’m seeing Fresh 80, Panasonic FV-GKF32S1, and ASV-90 are options.

If I go with a ducted system, I’m considering spot ERV/HRVs, a whole-house ERV/HRV hooked into the ducted system (I’ve read here that it’s ideal to have an ERV/HRV running air through ducts separate from the heating/cooling system, but that’s not practicable with my old house), or two WhisperGreen exhaust fans paired with an central-fan-integrated supply (with FanCycler, Aprilaire 8120, or other). If I went with the central-fan-integrated supply, I’d probably try to adjust the WhisperGreen fans and AirCycler to get slightly positive pressure (I like the advantages of positive pressure highlighted in the ‘Supply Ventilation’ page on this site).

So I’m hoping that someone here might have feedback (i.e., for the ductless and ducted scenarios, which would ventilation system would work best without being really costly to install or operate?) based on their expertise as an industry professional or based on their experience as a homeowner in similar circumstances.

Thank you for your time.

Notes: I’ve tried to educate myself, including by reading the following pages on this site:
– Designing a Good Ventilation System,
– Fresh air for mini-splits,
– Seeking ductless fresh air supply for balanced ventilation,
– Supply Ventilation,
– Exhaust-Only Ventilation Systems,

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  1. GBA Editor
    Martin Holladay | | #1

    First of all, can you tell us your name?

    It's going to be hard to give you advice. You've done your research.

    Since it's your house, you can't really delegate the decision-making. It's time to step up to the plate and make a decision. Look in your wallet and see what you can afford, and make your choice.

  2. Expert Member
    Dana Dorsett | | #2

    Are you sure it's 2x6 framing in the walls? Are the walls insulated? Most 1920s houses were 2x4 framing, often full-dimension 2x4s, with full dimension 2x6 rafters, but I've never seen a 2x6 wall in a house of that vintage.

    The Lunos e2 units are pretty easy as a DIY retrofit, but the 2 paddle switch control to set the operating speed/mode is something only a binary-arithmetic junkie could love. 475 has an overpriced encoded switch to allow one-knob control (for $50), that's a lot more intuitive for most people. Measure the wall thickness carefully- you'll probably want the shorter version, or build an insulated console enclosure around the longer (higher recovery efficiency, with the longer ceramic core) version.

    Unless the duct system is really well sealed and well balanced, in a leaky house simply cycling the air handler may be driving more ventilation air than what came through the HRV.

    If the basement isn't air sealed and insulated it should be, since soil gas infiltration is the opposite of "clean".

    Even the smallest gas furnaces are oversized for the typical heat loads of an insulated 1000' house on a 1000' basement in coastal WA/OR/B.C. Even if you're already on the gas grid there's little to no cost advantage to going with combustion heating compared to mini-splits. Gas/heat pump hybrids really don't make much sense in that climate either, since the heat pump will be operating in an efficient outdoor temperature more than 99% of the time. If you're going to heat with gas, micro-zoning room by room with thin profile hydro-air coils running off a condensing water heater makes more sense than "dual fuel".

    With a heat pump solution sized correctly for the loads you won't need much heat-strip (if any) to cover the additional load that happens on those rare days when it drops to single-digits F outside, no need for the fossil-burner backup.

    If you have a heating history on the place, use wintertime fuel use correlated with heating degree-day data to get a better estimate on the as-is-where-is whole house heat load, as detailed here:

    Oversizing a gas furnace has very little impact on efficiency, but with heat pumps (including mini-splits) oversizing can take a huge bite out of efficiency. Bigger is the opposite of better.

    A typical leaky 1000' insulated 2x4 house over an uninsulated 1000' basement, with clear glass storm windows over single-pane wood double hungs will still come in with a heat load under 20,000 BTU/hr @ 25F. If the foundation get insulated it could be under 15,000 BTU/hr. If the framed walls aren't insulated it might be as high as 30,000 BTU/hr, but in those cases fixing the air leakage and insulation deficits would be at equal or higher priority to active ventilation or new heating systems.

  3. GWVM | | #3

    Martin and Dana: Thank you for your feedback. The house might have 2x4 framing in the exterior walls. I'll have to take another look. I will also investigate to make sure the sizing is correct for a heat pump (the HVAC companies have recommended either a 45,000 or 48,000 BTU Mitsubishi heat pump). I have been hesitant to do a ton of insulation because I've assumed that the costs would not be worth the energy savings and improved comfort. Perhaps I should take the idea more seriously and at least consult with a company on what would be involved. Thanks.

  4. Expert Member
    Dana Dorsett | | #4

    Seriously, FOUR TONs of heat pump? Even with no insulation and a ductless head in every room that's overkill!

    Air sealing and insulation may not pay back super-quickly on raw electricity/gas prices, but it pays back immediately in comfort, and in your case, smaller-cheaper HVAC solutions.

    Even the three-ton Mitsubishi MVZ big-duct air handler is good for 40,000 BTU/hr @ +47F, and probably overkill for your actual loads:

    The 3.5 and 4 ton multi-split compressors are capable of even more output with ductless ore mini-duct cassettes rather than the full-sized air handlers.

    In know someone in Kitsap County WA heating an 800' double-wide mobile with little to no floor insulation using a 1.5 ton ductless Mitsubishi with a max capacity of about 21,600 BTU/hr @ +17F, and small electric baseboards in both of the doored off bathrooms. With no insulation in the walls and lots of air leakage your load is probably higher than that house, but with insulation it would surely be lower.

    There may be decent subsidy money available for retrofit insulation, depending on location and utility company. Where are you located?

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