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Zehnder Q350 using NON-Zehnder air delivery system

kermit49 | Posted in Mechanicals on

Designing in a Zehnder Q350 for a 2100 sf one level, Zone 3 good enough house.

I like the Zehnder ERV but will not run (18) 3″ flex ducts, many runs a lot longer than 35ft. Zehnder “designed” the system at 100 cfm which I am ok with.  I do not like the Zehnder delivery system design and especially what they charge for them. 

I prefer hard ducting and non-Zehnder flow adjustable supply and extract diffusers.

Anyone gone or know someone that went this route? If so, what issues might have been encountered like Zehnder not honoring their warranty? no commissioning service (if needed), customer support, etc.

Anyone commission their Zehnder ERV?  Results?

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  1. Trevor_Lambert | | #1

    I bought an HRV from them and supplied my own ducting. They didn't bat an eye. I was offered commissioning, which I deferred indefinitely and ended up doing myself. I received extensive customer support in relation to problems I had with my building inspector.

    1. kermit49 | | #2

      Thank you This Page. That's certainly good to hear.

      There is something wrong with designing long runs with 10-12 cfm per 3" flex ducts. Many registers of mine needing two, 24 cfm. For flows higher than mine, I see they offer a (3) 3" ducts register. That's crazy!

      Don't know if your customer support was directly from Zehnder or your assigned dealer. I am to work with Small Planet Supply as I am in the western states.

      Thank you for your re-assurance.

      1. norm_farwell | | #4

        I’ve heard of folks doing the inverse—using zehnder distribution components on a less expensive unit like renewaire.

        I like the components a lot—the labor is minimal, the tubes fit in standard 2x4 stud cavities, the registers are very well designed and can be easily adjusted for accurate balanced flows.

        Yes, they are expensive. But you get what you pay for. I wouldn’t want to try to hard pipe one of these.

      2. Trevor_Lambert | | #10

        There's no dealer in my area, so I was dealing directly with Zehnder.

        You are right to be concerned about flow rates and duct sizes. Make sure your design allows for the full capacity of the ERV, which I think is about 210cfm. I'd even recommend going up to the Q450 or Q600 if your budget allows. 100cfm sounds fine for the expected standard occupancy for a house your size, but quickly falls behind if you have company over, especially if they're grouped into one area (as would be typical) as opposed to spread throughout the house.

  2. Deleted | | #3


  3. kermit49 | | #5

    Norm Farwell, I see others doing just what you mention. This speaks well for the Zehnder air delivery system. There is no question Zehnder components are quality components.

    If my system was more centrally located and maximum run not as long as they are now and I could use the smooth wall tubes instead of flex duct, then it would be tempting despite the cost.

    Yes the flex ducts fit in a 2x4 wall cavity but running it horizontally from stud to stud destroys the 3-1/2" wide stud.

    I like minimal installation labor too, but I prefer to have a delivery system with low pressure drop, low velocity baked into the design even more.

    1. norm_farwell | | #7

      If your runs are less than 50’ I wouldn’t worry at all. And you certainly have margin on the static pressure to go longer than that if you’re only looking to deliver 100 cfm.

      On a recent project we found we had to hard pipe trunks to various distribution manifolds and we used comfoflex to connect to the registers. We usually do a dropped ceiling to be able to run tubes and wires easily. Wall registers are also an option.

      If you are concerned, I would draw out a plan and run it past zehnder. Last I knew they have somebody who can do the pressure drop calcs in cases where that’s a concern.

  4. Expert Member
    Akos | | #6

    The Q350 is a box that moves air. As long as you stay within the pressure limits of the unit (less than 0.8" wg including exterior ducting and wall cap at 200CFM) the system will work.

    The one thing to watch for with hard ducting is noise. These units are quiet but not noise free. You want a system where you can't hear the unit ramping up to boost especially in bedrooms. This means including an inline duct silencer at the unit on both supply and stale air pickup trunks or lengths of flex duct, even better, include both.

    You can also look at the flex ducting and vents for high velocity systems. Some come in 3" which is easy to fish in a 2x4 wall. Not cheap though.

    Instead of multiple small duct runs, you can bump up some of your interior walls to 2x6, this lets you run 4" or 5" flex duct for places where you want more flow. If this is done inside a closet it is not noticeable at all, this is what I did for my home.

  5. kermit49 | | #8

    Boy, you guys make convincing arguments. Am open to changing design but will need to take second look at hurdles that got me here in first place.

    Akos, I know 3" ducts will vertically go down 2x4 wall cavity, just not horizontally without eating a 2x4 for lunch. I agree on eliminating noise as much as possible, especially near bedrooms. I will use flex where needed for that purpose.

    I only have soffits to work with, no attic nor basement, and already they also house HVAC ductwork. Am limited to soffit size and their numbers if room is to look good. ComfoWells manifolds are physically not well suited to being inside a soffit. They are big and port location not where needed. Only place left for these manifolds is near the ERV and so run length do not get reduced much. My quote warns that exceeding 35ft run will affect flow. I know the ERV can do 0.8 iwc.

    My supply and extract diffusers needs to be mounted vertically or horizontally on soffit. That seems to rule out Luna-S. I assume the Luna-E (extractor) will work mounted on a soffit. Yes? No? The other offered register box has ports located so that it's impossible to connect to unless the soffit depth to ceiling is a lot more than the 12" planned.

    Norm Farwell, I did send Zehnder my layout and surprised when the recommended runs were way past 50ft, some 85ft! It was the dealer that warned against 35ft. At any rate I know how to read their published duct performance curves and can see the pressure drops. I design the mini-split ducted HVAC system using pressure drop method and that came out very well.

    Norm, you also mentioned wall registers. I looked at them and prefer the models with opposite blade dampers (OBD) grills. Have you used these or with standard grill dampers? These would fit perfectly on side of a soffit.

    Still, will re-visit this and might need to mix components with 3rd party ones that fit.

    Gentlemen, appreciate advise coming from real experience users.

    1. Expert Member
      Akos | | #9

      You can run 3" duct across in a 2x4 no-load bearing wall. Use mending plates to splice the studs where they are notched after the ducting is in. Looks ugly but it hold up just fine once drywalled.

      If you are using a ducted mini-split, I would go for hybrid ducted setup. Since these are modulating units, the mini-split blower will be running 24/7 already, there is no problem with using it for distributing fresh air. I'm struggling to come up for a good reason for the added cost and complexity of running a 2nd set of ducts for fresh air supply only. This also gives you conditioning of the fresh air supply, although this is much less important in your mild climate. The stale air pickups should still be individually ducted (kitchen, bath, basement/crawlspace) but there are generally fewer runs so it doesn't take up all that much space.

      Generally when it comes to ducting, overall length doesn't matter much. It is all about friction rate, you can run very long ducts with pretty low loss as long as they are big. 200' equivalent length runs are not unusual in houses.

      P.S. Zahnder is nice but a bit overkill in Zone 3, there is practically no energy saved by using a high efficiency ERV. I would go for a much cheaper ERV that has ECM blowers.

  6. kermit49 | | #11

    Hi Akos.

    Not sure I want to build a hybrid ducted mini-split system. First I do not expect to run the mini-split 24/7. I could be wrong as I've never had one before.

    Our retirement home we will be building soon is in southern Utah where temps can reach 115 F summer and high 20's low 30's in winter. They do have nice shoulder seasons and I can't imagine running the ducted mini-split year round. Worse case run only the 9k ductless in the common area that can reach whole house if doors left open. House will be very well sealed and insulated. Also the Zehnder will switch on by-pass mode and deliver "conditioned" air courtesy of mother nature. We live in southern California now. We are one of thousands of families escaping each year.

    I agree with friction rate being key. I design for larger diameters with slower flow, so distance not a big issue.

    Funny you mentioned using a cheaper less efficient ERV. I did look at a few recently but the price difference on the unit itself was not as great as I expected. Not comparing the under $2000 ones. The Panasonic 200 cfm Intelli-balance runs around $2500. About half the Zehnder Q350, It's all the Zehnder specialty accessories, flex ducts, diffusers, etc that can easily double the purchase cost.

    Akos, as always thank you for your perspective.

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