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Community and Q&A

Path for Mechanical system upgrades

John_H12 | Posted in Mechanicals on

I have a newer home, 2,100 square feet climate zone 3. I’ve paid for air sealing but the insulator cautioned that I need to be careful with the tightness.  I assume this is because I have low efficiency natural gas furnace and water heater that use indoor air for combustion.  I want to finish air sealing the basement band board leaks, but am concerned I may need to replace my furnace and water heater first. 

What are the right next steps? Air seal and add a a outside air vent? Air Seal and get a CO2 monitor? Get a blower door test (I’d like to air seal while the blower door contractor is on site).

When do you upgrade the water heater and furnace? Seems like a waste to replace them because they are only a year old, but I also don’t want to kill myself with CO2.

I’m not clear on the next steps for upgrading.

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  1. Expert Member
    NICK KEENAN | | #1

    Get a CO monitor. Do a blower door test. There are ways to provide makeup air. It would help to know the make and model of the existing fixtures.

  2. chicagofarbs | | #2

    Hi John

    You could consider an Energy Recovery Ventilator (ERV) or Heat Recovery Ventilator (HRV) to continuously bring in fresh air and exhaust out stale old air.

    There is also a neat produce by Build Equinox called the CERV that is a smart ventialtor, it monitors CO2 and VOCs and only brings in fresh air when needed.

    I'm sure others would agree that there is a tipping point on building tightness without having a means of bringing in fresh air mechanically.

  3. charlie_sullivan | | #3

    Get a good low-level CO monitor. Not just one that alarms if it's about to kill you, but one that can read 10 ppm or lower. Some good ones:

    Also get a CO2 monitor. That won't kill you, but it's a good way to tell whether you have enough ventilation.

    1. johnwtaylor | | #4

      We have 4 of the CO Experts PG 2017 and 4 of the household CO alarms.

      With our car running 20' outside the basement door the CO Experts will alarm at 5ppm and will reach 30ppm while the household CO alarm shows nothing and does nothing.

      Household CO monitors will keep you alive but they won't keep you healthy.

  4. John_H12 | | #5

    Thought about an ERV, but the ones I've seen have an exhaust fan. Not sure that would help with the potential negative pressure and back drafting.

    Thanks for the links and info for the CO monitors.

    The furnace is Trane model S8B1C100M5PSAAA 80% AFUE 80,000 btuh. The water heater is a Bradford White RG250T6N 50 gallon 40,000 btu/ hr.

    I've seen the negative air pressure calculation worksheets and I can engineer a "hole" in my house. But that seems like a waste. I crack open my sliding glass door when the range vent fan is on. I get a lot of complaints when it 5 degrees outside.

    I've read articles that the water heater is the supposedly the worse back drafting appliance. So I'm thinking that should be the first item to replace? I'm nervous about a heat pump water heater, my incoming water temperature gets down to the high 50s in the winter

  5. user-723121 | | #6

    How tight is the house (ACH50) and what is the volume in cubic feet? The furnace is likely using more makeup air than is the water heater. I would not get excited about replacing almost new equipment. There would not be much energy penalty in Zone 3 by providing makeup air from the outside into the mechanical room.

  6. charlie_sullivan | | #7

    Your water heater has an energy factor of 63%, meaning that's the efficiency after factoring in standby loss. Given that you also use it all year, that might be the one to replace first, although Doug is right that the furnace needs more (twice as much) makeup air.

    No worries about 50 degree incoming water temperature for a heat pump! We use them up here in New Hamphire with much colder water (and colder basements) with no problem.

    I think the ERV suggestion is for general fresh air supply, not for makeup air.

    5 F in climate zone 3? That's unusual for most of Zone 3, which makes me curious where you are.

  7. John_H12 | | #8

    I'm in St. Louis Missouri and like most areas we are experiencing some cold weather in February. I've probably looked at the wrong climate zone map, maybe we are 4?

    The insulator said they used the recent energy star guidelines but did not do any work in the basement. I've already found and caulked some sill plate cracks. There is a foam sill sealer in place, but the seal to the foundation looks marginal.

    I can look at an engineered hole to the mechanical room. Is there a preference for using a motorized damper tied to the furnace or a cape damper?

    1. Expert Member
      NICK KEENAN | | #9

      Does your water heater have electric controls or is it all mechanical? With an electric-controlled one you can attach a relay that senses when it's running and use that to control a damper. If it's all-mechanical that isn't really an option.

      1. John_H12 | | #11

        Unfortunately this heater doesn't have a motorized damper. The controls look like they are electric but powered by the heater. There's no power connection

    2. charlie_sullivan | | #12

      Yes, you are near the northern edge of zone 4, nearly zone 5. That fits better with your temperature. Your heating design temperature is 2 F, so 5 F is quite reasonable.

  8. John_H12 | | #10

    OK scratch the cape damper as I just read that the passive make up air strategy doesn't work.

  9. Expert Member
    NICK KEENAN | | #13

    You can get a direct vent 50 gallon water heater for about $850, or a tankless starting around $700. The one you have was probably about $500 new and you could probably sell it on Craigslist for half of that. So it's not that expensive to upgrade the water heater to one that pulls outdoor air. The furnace you can hook up to a power damper to bring in makeup air. Once you have both pulling outdoor air for their combustion you can seal to your heart's content.

  10. John_H12 | | #14

    DC, ok thanks, sounds like a plan I can start working on

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