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Does 7-10% SRE matter on an ERV?

Shawnnixon1 | Posted in General Questions on

I’m deciding between 2 Venmar ERV

1. A160E65Rt: 150CFM @0.2 65% SRE at 0c, 57% at -25. $1637

2. A160E75Rt: 140CFM @0.2 75% SRE at 0c, 64% at -25 $1536

2000sq ft home
Montreal Canada 

is it better to get the 100CFM extra or the extra 7-10% SRE?

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  1. DennisWood | | #1

    I would say that it depends on how you plan on connecting it. In Montreal, dead of winter, delivery temps will be below ambient so if you're interconnecting to the furnace, it won't make much of a difference.

    I would 100% always go with the more efficient unit though as your pre-heat costs will less, as will your post-heat costs. You will find efficiency goes up as air flow drops, so at say 70 CFM, the numbers will be better. Those units you mentioned have ECM motors, auto balancing etc. so should be good choices.

    1. Shawnnixon1 | | #3

      I have baseboard heating no furnace

  2. Shawnnixon1 | | #2

    I dont have a furnace no hvac only baseboard heating

  3. DennisWood | | #4

    How is the fresh air being ducted? You will see temps below 15 C on delivery so where you dump that air, and how much in each room will determine to what level you'll want to consider pre-heat or post.

    Pre-heat makes more sense to me as it will increase your ERV ventilation run time, potentially keeping it out of cold temp recirc, and allow you to lower your CFM delivery as well. Hydro in Quebec is hydro generated and electric pre-heat makes sense for you.

    Preheating requirements will depend a lot on your CFM delivery. At 40 CFM, 1000 watts will do, but as you exceed that, you'll want higher capacity.

    No one has asked yet, but how tight is your house? Has it been blower door tested? I ask because if it as old build that is leaky as heck, no point in an ERV until all that is addressed :-)

  4. Shawnnixon1 | | #5

    Hey thanks for your help, house is built in 2004 and I know its somewhat tight as co2 build up 1000-1200ppm verified by aranet4 and 5 other meters. As soon as we leave the house and i open windows and close it stays at the level we left so its us breathing lol. My goal is to get this co2 out, bathrooms have their own exaust fan 100cfm. I will do one suppy and one return on main floor, top floor will have 1 supply and for basement should I do supply or return?

  5. DennisWood | | #6

    1000 to 1200 ppm is not crazy tight, but it will drop with an ERV for sure.

    I'd try and split up your supply as much as you can. I'm dumping 100% into the main living area, and it does cause a few challenges as that is also where the main thermostat is. Now if you're heating with electric baseboards, this won't matter as much as the units in that area will do their job to post heat. Focus on your sleeping and main living areas for supply. If you can, try and return from your kitchen. A supply won't hurt in your basement, and if it's damp in summer, it makes sense to have a return there as well.

    I just added a 14x14x4 inline filter box to our home system and 100% would recommend that if you have room. ERV/HRV filters are too small/restrictive at any decent MERV level.

  6. Shawnnixon1 | | #7

    If i can have only one option return or supply in basement what would it be?

  7. Shawnnixon1 | | #8

    Can I expect the 1000 ppm to drop to 500?

    1. Expert Member
      Akos | | #9

      Short answer is no and you don't want to. That amount of ventilation costs too much energy in colder climate. 700 to 800 is reasonable and feels plenty fresh.

      As for the original question, there are two things. Operating cost and supply temperature in the winter.

      In terms operating cost, you are probably somewhere at 7500 heating degree days (imperial). Assuming 100CFM ventillation the yearly enregy cost is about:

      7500HDD*24h*100CFM*1.08Btu/cfm*(100%-65%)=68 Therms or 1992kWh

      Bump the efficiency up to 75%, you are down to 48 Therms or 1406kWh

      You have cheaper hydro but at my current electricity costs, the upcharge for the better unit pays for itself in a bit over a year.

      At your design outdoor temperature of -20C, the 65% efficient ERV would supply fresh air at 6C, the 75% unit at 10C.

      From my experience with a 72% unit at home, this is the bigger issue unless you install a post heater. Neither unit supplies air warm enough.

      If you go with the Renewair EV Premium L at 90CFM, you are at 83% efficiency which means 13.2C which is workable without a post heater.

      You generally want a stale air pickup in the basement. This way any basement smells or radon can be exhausted. This will also draw warmer conditioned air from the the upper levels into the basement which is a bonus.

      1. Shawnnixon1 | | #10

        Thanks but I’m not looking to save money, the main priority is to bring down co2 levels to 500ppm or so my friend has fantech hrv similar sized home 159cfm instead of 133 that I’m getting hopefully it will do the job? If i crack open a window a tiny bit on both side of my house the co2 drops to 470

  8. Shawnnixon1 | | #11

    The main issue for me is I have a saltwater coral business from home and I’m paying too much $$ on co2 scrubber and I dont mind paying 80$ on more electricity per month vs paying 160$ on co2 scrubbers haha

  9. DennisWood | | #12

    You won't get to 500 PPM throughout your whole house with occupancy, without pushing a LOT of air as Akos has mentioned. I see 600-800 at 50-70 CFM with four family members and two cats, with peaks in the morning (bedrooms) around 900 PPM. Total area about 1800 + basement.

    There is a big difference on very windy days as you may not need any ERV runtime to keep levels under 700. This all depends on how tight your home is.

    I guess you'll want a return in your salt water coral room :-)

  10. Shawnnixon1 | | #13

    So how much cfm do i need to make it 500?

    1. Expert Member
      Akos | | #15

      First you should focus on where the corals are. You want a dedicated fresh air supply there, there is no need to overventilate the whole house. How much CO2 do the corals produce?

      1. Shawnnixon1 | | #19

        I will have a supply right where the corals are … but now I’m worried if the 133cfm is not enough and I should just cancel tomorrow and get the Panasonic Intelli balance 200CFM for 500$ more plus tax

  11. Shawnnixon1 | | #14

    Cracking a window 1 inch front and back of house makes it 450ppm ….. erv cant?

  12. Shawnnixon1 | | #16

    For same price I can get Fantech atmos 200e 200cfm but the defrost type is FAN Defrost and Vanee is damper defrost

  13. DennisWood | | #17

    Cracking a window at both ends of a house with a breeze, (or just checking on a windy day) can bring C02 levels down surprisingly quickly. However, at 20C, you'll use a lot of energy to heat that air :-) ERV/HRV remember is dilution and typically at lower rates. What you are hearing here is that 600-800 is a good target, and that 500 is doable, but you'll have to bring ventilation rates up quite a bit to do it.

  14. Shawnnixon1 | | #18

    Thanks alot for your help this ERV cost me 1500 plus tax, I see the Panasonic Intelli Balance 200CFM is 2000+ tax, should I get this instead? I just placed the order today for Vanee but I will cancel it, please let me know

  15. DennisWood | | #20

    I like the Panasonic products. You have a "special" case with the coral business (which sounds pretty cool btw) so the higher CFM unit does give you more room to increase ventilation if required. 86% efficiency at 0C is quite good on that unit.

    That said, Venmar, Vanee etc are all made in Quebec to my understanding so service should be pretty easy on those products :-)

    If it was me in your situation, I'd look at the Panasonic as you'll end up with decent actual measured flow once you fully duct your system. You'll need to balance the unit which is pretty easy to DIY if you pick up a differential magnahelic gauge. This 0 to .5 unit will work:

    1. Shawnnixon1 | | #21

      Thanks so much, I have a technician who will install it, Venmar obviously parts will be easier and their new controller sounds awesome will tell you how much cfm is running, self balance all the time, you can weekly schedule your modes etc, but then will I really use all this? Hmmm the store ai bought Venmar said for 2000 sq ft home 140cfm is MORE than enough, this is really confusing ugh!

  16. Shawnnixon1 | | #22

    If 140cfm wont be enough or I will be running near max and still its a maybe to bring down co2 levels to 500 I rather get the panasonic IB200 hopefully that has damper defrost and not fan defrost? Cant find this info anywhere, please let me know if I should get that instead

  17. DennisWood | | #23

    The Panasonic unit uses a third center damper to defrost via internal recirculation.

    140 CFM is a lot, however one needs to consider how C02 intense your coral business is. Also, 86% at 0C will provide fresh air that likely won't need post heat if you're careful with your supply locations. Remember that the efficiency numbers are not tested at max CFM. As you increase CFM, the efficiency will drop. So at 100 CFM, the Panasonic will likely be doing much better then the other models you have indicated likely because it has a larger core.

    If your goal is 500PPM, then the larger unit will make it easier/more efficient to get there.

    1. Shawnnixon1 | | #25

      Please advise

  18. Shawnnixon1 | | #24

    Thanks alot, I might also move in 2 years to bigger home, and will take my ERV with me lol maybe the Panasonic will be a good choice too bad waranty is 3 years on everything else. Co2 right now is showing 1200ppm Yes I need it to be 500-600 max. The store told me whether its 100cfm or 200 it’s all the same it will just take longer for the 100cfm to exchange air and if u run in 24 7 it will remove all the co2 out which is why I placed the order to save 500$ by not buying panasonic. A third center damper defrost? Is that good?

  19. DennisWood | | #26

    Any unit that uses a recirculation defrost strategy will have an internal bypass damper that is open for defrost so that when the exhaust air/intake air dampers are closed, there is a path for air to recirculate internally and warm the core.

    1. Shawnnixon1 | | #27

      Thanks everyone, I took your advice and went for the Panasonic 200cfm unit hopefully made the right choice

  20. DennisWood | | #28

    Any of the models you mentioned would work, however the higher efficiency/delivery temps and CFM range (you might need this for your coral) of the larger Panasonic unit means you won't regret the purchase :-) If you don't run it at max capacity, you'll still see the increased benefits of the increased efficiency at lower flow rates.

    For those of us in cold climates, efficiency should be at the top of the shopping list IMHO. At 86%, following Akos' calculations, your added heat energy cost should be below 1000kWh. With ECM motors, actual power use will likely be in the 50-60 watt range at 100 CFM.

    1. Shawnnixon1 | | #29

      Dennis you are the man thanks!

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