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Community and Q&A

Make-Up Air Heaters to Balance a Range Hood

Litawyn Eco-House | Posted in Mechanicals on

I’ll be breaking ground this Fall for a new home in Maine that will be small (1,214 sq ft) and super-insulated. Heatload requirements are estimated to be around 9,100 Btu/h in the dead of a Maine winter to keep the place at around 72F. One challenge I’m facing is maintaining the thermal efficiency of the home when using a gas range top and ventilation hood on a regular basis. I’m an avid cook committed to cooking with gas and have pieced together a Make-Up Air system that I believe will pull in and preheat air in the colder months at a rate equivalent to the amount of air being exhausted by the range hood. I want a solution that will eliminate the possibility of bringing a cold blast of air into the house every time I use the range top in the winter. Also, if I do install such a system, I curious to know if I should have the incoming air vented directly into the kitchen or whether it would be sufficient to have it brought in through the basement.

Here are the specifics for the system:

1) 36″ LP gas range top that will likely never be burning more than 60,000 Btus at a given time
2) 42″ range hood with 600 cfm inline blower (sized for a maximum of 65,000 Btus) venting to the outdoors
3) Self-contained 10 kW (600 cfm) make-up air heater and intake
4) Automatic make-up air damper with digital controls

There will also be a Zehnder ERV in the house running at all times and exchanging air at a rate of 78 cfm (9 to 10 air exchanges per day.)

Is a Make-Up Air system like this overkill? Are there other less expensive or more reasonable options (short of cracking open a window) that I should be considering?

Finally, in there not a way to harness any of the heat produced by the range top to help preheat the make-up air being pulled into the house, much like a GFX recoups energy from a shower drain? Simply blasting that heat out of the house seems like such an incredible waste of energy that should somehow be able to be recouped, if even just partially.

Thanks for any feedback or suggestions.

Litawyn

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Litawyn,
    Your suggested makeup air system will work, although (as you clearly know), the makeup air unit is an energy hog. My own advice: run the range hood exhaust fan as little as possible; include an override switch to disable the makeup air unit when you want to; and experiment with cracking a window open.

    For more information on this topic, see Makeup Air for Range Hoods.

  2. Expert Member
    Armando Cobo | | #2

    Dakota Supply (They bought Shelter Supply) in MN sells heated MUA units.

  3. Litawyn Eco-House | | #3

    Thanks for the advice, Martin. I'll definitely add an override switch to the makeup air unit and only use the range hood when it's mandatory. I am curious though whether there are cost-effective ways of harnessing the heat being blown out of the house via the range hood, possibly transferring some of it to the makeup air system. Is this just overkill? It would be a shame not to be able to recoup at least some of that energy, considering the range top could be producing 60,000 Btus at a time.

    Thanks again.

    Litawyn

  4. GBA Editor
    Martin Holladay | | #4

    Litawyn,
    You don't want to try to build a homemade HRV using range-hood exhaust. Nor do you want to tinker with a system that lowers the temperature of the range-hood exhaust with cold water tubing. The reason is simple: range-hood exhaust is full of cooking grease, and you want that exhaust stream to leave the duct, hot and fast -- not cold and sludgy. All attempts to recover heat from such ducts had accelerated the accumulation of gunk on the duct -- kind of like creosote on a chimney flue.

  5. Litawyn Eco-House | | #5

    Makes perfect sense. The visual really helped :)

    Litawyn

  6. GBA Editor
    Martin Holladay | | #6

    Heath,
    Q. "Wouldn't the range be producing enough heat to offset the energy loss from the hood?"

    A. No.

  7. Heath Lansdowne | | #7

    Hi all, just a thought, but wouldn't the range be producing enough heat to offset the energy loss from the hood? the makeup air will have to come in somewhere, i know and it will be cold, but the net energy demand should remain about the same. the hood will only be used while the range is producing heat that is superfluous to space heating anyway, it's just a by product. obviously you are consuming energy and then pumping it outside, which is a waste, but if the house is well insulated you must be able to store this excess heat from the range that you want to recapture or the place will overheat. if it's not super insulated, then the net effect will be near enough to 0. unless you're looking at building a Passivehouse certified home, i don't think the net loss will be significant. it's not like in a bathroom where the fan simply pumps heat outside that must then be replaced by the heating system. somewhere, someone knows the math for this. just a thought.

  8. Richard Patterman | | #8

    I have a question. Does a gas range require more ventilation than an electric range?
    Seems with a gas range you need to remove both cooking odors and byproduces of combustion. With an electric range, just cooking odors. I know they sell kitchen vents that just filter the air with no outside discharge. I'm guessing they can only be used with electric range?

  9. GBA Editor
    Martin Holladay | | #9

    Richard,
    There are at least 4 reasons to operate a range hood fan:
    1. To remove moisture.
    2. To remove odors.
    3. To remove smoke (usually when cooking meat).
    4. To remove the combustion byproducts from gas combustion.

    #4 doesn't apply to electric stoves.
    #3 doesn't apply to vegetarians.
    #2 doesn't apply if your food smells good.
    #1 applies in all cases.

    Remember, operation of the range hood fan is optional, and entirely under the control of the cook.

  10. Robert Hronek | | #10

    Martin

    If I am scrambling a few egg on an electric stove do I need a fan. Or say a small pot of pasta with a lid. I am not sure you always need a fan.

    Now if you have an gas range or oven then you need a fan.

  11. GBA Editor
    Martin Holladay | | #11

    Robert,
    It's your house -- you get to operate your fan any way you like.

    Just like you get to choose whether you like your eggs sunny side up or scrambled.

  12. Aj Builder, Upstate NY Zone 6a | | #12

    Martin, such wisdom, to scramble or not to scramble. Whether tis noble even to break thy eggs, indeed..... Alas we must post on and thence.. be gone.

  13. James Morgan | | #13

    Musings on Martin's list:
    Moisture, smoke and combustion products for sure, but good luck if you hope to keep cooking odors from pervading the whole kitchen area with just a range hood. Scent molecules disperse differently than the much larger moisture and soot particles, and the human nose is sensitive to very small concentrations of common cooking ingredients like sauteed garlic, onion & cabbage and many fried, roasted and broiled foods. With today's open plan interiors the kitchen area often includes the living and dining areas too. If you don't happen to like such smells you're not going to enjoy your home cooking very much, no matter how many cfm you have rattling away over the stove. Come to think of it those open-plan interiors could be why takeout dinners are so popular these days, even (especially?) among the gourmet kitchen crowd.

  14. Aj Builder, Upstate NY Zone 6a | | #14

    Not relative, but like to eat home or at a nice restaurant. I have never ordered out and most likely never will. The thought of eating warm food from a foam box.... You're killing me.

    And as to smelling the food cooking? That's one of the best parts of cooking. Prepping food together. Sampling as you cook.

    Who wants to eat food you can't smell wafting from the kitchen??? I'll pass thank you.

  15. Litawyn Eco-House | | #15

    I'd have to agree with AJ. If you don't like how a particular food smells, why in the heck are you cooking it, much less putting it into your mouth?

    Litawyn

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