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Munchkin fresh air and vent routing

Brad White_9
Brad White_9 Member Posts: 2,440
Unless that is specifically sanctioned in the HTP literature, I would not go out on my own with that one. Most ModCons want balanced pressure between intake and exhaust. Imbalance will get you problems.

You cannot tell me that the ambient pressure in the attic is the same as that outdoors or consistent.

If the literature has a specific application for what you describe that is one thing. Otherwise, do what they tell you.

My $0.02



  • Gene Davis_2
    Gene Davis_2 Member Posts: 71
    What about this?

    We'll have a wall-hung T80, and want to route its PVC sch40 vent and fresh air intake up from the boiler room, inside an interior 2x4 framed wall above, into the cold attic. The vent will then up through the roof, but the intake will terminate in the cold (and well vented to the outside) attic.

    Sound OK?
  • jp_2
    jp_2 Member Posts: 1,935

    i thought you said your heatload was around 30,000?

    why the 2.5x larger boiler?

    why would you want to terminate the intake in the attic?
  • Gene Davis_2
    Gene Davis_2 Member Posts: 71

    Why not in the attic? Why not, thought I.

    The trussed roof structure has its deck fully vented, by means of continuous louvered soffit venting all around the building. Nice cold fresh air, all winter long, and I've no reason to believe that the attic is at any other pressure other than atmospheric.

    Besides, that is the way my super-pro heating contractor did the air intake for the WM Ultra he installed on a project for us last year.

    We are in deep snow country, and going outside for the air intake always raises questions of how to get high enough.
  • Gene Davis_2
    Gene Davis_2 Member Posts: 71
    Load is 36K

    And the T50 might be a good choice. I think the turndown is the same, T50 versus T80, and since we've DHW to do, we thought the bigger one might fire up the water more quickly, and also fire up the house more quickly if the owners just occupy it on weekends.

    Cost diff is pretty minimal between the T50 and T80.
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,541

    a wise man once said"the urge to oversize is greater than the sex drive" Truer words were never spoken

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  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Unless your emitters can accept the additional input, the increased capacity of the boiler is nearly wasted and it will only fire at full output until the water in the system is fully heated.

    Believe you're using generously sized panel rads--you'll need to ensure that some sort of temperature "boost" is available for the reset curve--either automatic or user-controlled. Otherwise the panels can only put out as much as the room temperature and normal reset curve will allow. If you've sized the panels for 140F average water temperature at design, you can expect about somewhere around 2x the output at 180F average water temperature in a 55F or so room. With your low heat loss this may well wind up WAY less than output of a T80.

    Realize you have a basement slab with tube, but certainly it will be operating on mixed circuit to reduce supply temperature which will in turn reduce its ability to absorb energy from the boiler.
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