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what inline box filter for a hpwh?

cs55 | Posted in General Questions on

my tanked gas heater is currently leaking. have taken apart as much as i can, all valves seem good. seems to be coming from bottom of tank. but its in a cramped closed and difficult to see anything.  10 years old, lots of visible corrosion on the bottom of tank.

cant make up my mind between a hpwh and a tankless condensing gas unit.  i’m leaning towards an hpts-50 if tanked, or rinnai rx160iN.  the only gas appliance i have is the gas water heater and if i switched to a hpwh it would be about 20 months for the hpwh monthly energy cost to pay for the $700 price delta — excluding labor costs.

i live by myself and occasionally have people over. if more than one person showers in the winter with this  50 gallon gas water heater, it can empty out.  thats not often.

tldr;
mainly just thinking out loud; really no question there since this is pretty much a personal decision.

if i go with a hpwh i’ll need a good way to filter the air since the heater will be in a tiny closet inside of a very dusty garage. it will either be ducted in from the attic or from the front porch ceiling. exhaust would be ducted to the garage. door would be kept closed.

 would this work? https://www.amazon.com/AC-Infinity-Inline-Filtration-Ventilation/dp/B092114P97?th=1

or does anyone have better suggestions for filtration?

thanks

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Replies

  1. Expert Member
    Akos | | #1

    I think this is the fan in the unit:
    https://www.mouser.com/datasheet/2/120/ebm_papst_Data_sheet_US_W1G200EC9570_KM99943-3455603.pdf

    So you are looking at somewhere around 300 to 400CFM at maybe 0.05" WG pressure drop across the filter.

    I think that 8" unit is too small if you want a pleated filter. It can work if you use one of those spun mesh bug catcher type filters though.

    1. cs55 | | #2

      ty, your posts are always helpful.

      so itd be a better idea to go with a filter box made for a 10-12 inch duct and use an 8 inch adapter?

      1. Expert Member
        Akos | | #3

        It is not about the duct size but filter size. I would check the exact filter data you choose but you need about 20x20 filter. A bit oversized, but not too far:

        https://www.filtersfast.com/prodimages/FILTERSFAST-MERV-8-SPEC-DATA-SHEET-2019.pdf

        There are some return air grills that will take a duct. Might be the simpler install, you can put the grill on the wall to the garage and run the duct to it.

        1. cs55 | | #4

          thanks again

          https://www.ebay.com/itm/255656648407?itmmeta=01JEC5RQPTJHXCMYDZV2BEKWN2&hash=item3b8652ded7:g:Hh8AAOSwznpi6Bb1

          everything adds up so quickly. found some on ebay. if i were to get anything near the square inches of a 20x20 filter, ill need to have one custom made i guess. i have 16 oc ceiling joists, a 20x14 filter would be way less area.

          how did you calculate that? so we know that the water heater has integrated adapters for an 8" duct and the fan is 300-400 cfm from what you found.

          i saw some formulas online related to cfm and filter surface area, but i wasn't getting the 400 square inches you say i need. i trust your math way more than mine,.

          if this isn't too much of a loaded question; would it not be better to have the return air pull from the attic? its a ventilated attic that is extremely toasty in the summer and decently warm in the winter during the day. if i did go with a filter @ the return, it'd have to be

          on a side note; got that 160k rinnai for $1050 after taxes/shipping. have 60 days to return it. still unsure what to do. the labor cost for a hpwh and tankless are wild. i can find a dozen plumbers to remove my gas water heater and install a new basic cheap model for $1800-2000 all in.

          i can't find a single plumber to take out the gas heater, install a tankless for less than $2500 for labor alone. the same goes for the hpwh, which is also excluding me even bringing up the ducting situation.

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