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Community and Q&A

Warming a Cold Floor Above a Crawlspace

btymkiw | Posted in General Questions on

I have a brick ranch house in the Chicago area half basement and half crawl space. The crawl space side of the house main floor is colder than the side above the basement. On the side of the house with the crawl are two bedrooms with hardwood floors and a bathroom with tile. The 2nd bedroom floor is cooler and the room over all is cooler in the winter than BR1 (summer rooms feel about the same) The crawl has a concrete floor and appears to have a barrier of some sort where it has cracks. It was vented but no longer is- I have had closed cell spray foam added to the walls and rim joist on all exterior walls with no noticeable changes. In addition I have had the attic insulation removed, air sealed and reinstalled to code with cellulose. The flow of air on the supply side is almost nonexistent. I have had a hvac co come in they made several modifications to the duct work removing some bends and reducing angles adding a dampener to force more air into that Branch. It is the longest run. The hvac guy ( several people came by at one point looking at this and discussing) felt after a couple modifications (including adding a supply vent to the line to condition the crawl) felt the only options to fix this are an in-line fan that they aren’t confident it would help or two make the house into zoned area which would require all new duct work and a special system etc. I see how the improvements could increase the performance of the air flow and make the room warmer. But I don’t feel it would warm up the flooring. That being said the crawl doesn’t seem that cold when I’ve been in it since the spray foam was added. looking for suggestions to help warm up the floor. Also is duct sealing with aero seal worth trying to reduce loss of velocity and increase flow? walls showed insulation during an energy audit but of course not sure how much but did reveal two cold spot in corners of two exterior walls joining. I have pulled off wood trim around windows and added spray foam where I could.  Thinking of replacing windows not sure how old but not installed well and glass isn’t lowE

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  1. user-2310254 | | #1

    Are the rooms are actually colder than the rest of the house? How much colder? It sounds like you have a forced air system. How old is it?

    1. btymkiw | | #4

      Yes, they are on avg 3-8 degrees. I have an eco bee that has a secondary sensor that I’ve moved around.

      Yes forced air. I think ac is like 6-8 years and sane for furnace. I have had both serviced this year including a coil cleaning.

  2. Jon_R | | #2

    In-line duct fans will be effective at increasing airflow/heat. A supply and return in the crawlspace will make the bedroom floor warmer.

    > cooler in the winter ... summer rooms feel about the same

    Fixed HVAC balance is a myth - load ratios change with conditions.

    Adding some zoning doesn't have to be nearly as complex as they said. Can be as simple as adding a partially closing damper and a thermostat to control it.

    1. btymkiw | | #5

      I now have a supply in the crawl now.

      As far as a simple vs complex zoning I don’t know but if I recall correctly it was over 5K maybe even more. But yes it included another thermostat and replacement of that branch off the trunk

  3. plumb_bob | | #3

    It sounds like you are attempting to make the crawl a conditioned part of the house, which means it should be encapsulated to create an air and moisture barrier between the crawl and the ground/outside.. You are going to need to decide what the end goal is and then start checking things off the list to get there.

    What about adding a baseboard heater or similar into the crawl?

    Sounds like crawl space ventilation is something you should pursue, having both a supply and return from your forced air furnace in the crawl would help.

    Also, cutting in some floor registers so the air between the crawl and main house will be a good idea once some of the other issues are resolved.

  4. btymkiw | | #6

    When we bought the house 3 years ago it already had the concrete floor with what appears to be a liner under it. I guess with the exception of the return it is now an excapsulated crawl since it does have a supply.

    In the bathroom there is an access panel to the tub it isn’t sealed and is open to the crawl so there is that …

  5. walta100 | | #7

    It sounds to me like you are half way to a conditioned crawl space. Now for the bitter pill you must condition the crawlspace so that the crawlspace is more or less the same temp and humidity as the rest of your home.

    Plump bob let’s stop using the word “encapsulated” I see it as the language of the huckster salesmen and means almost nothing. The word “encapsulated” implies the crawlspace is somehow magically isolated interior and the exterior of the building leading to people to think they can get away without heating or cooling the space.


  6. plumb_bob | | #8

    Sure, encapsulate may be an industry term but the point is sealing for water, air, moisture and thermal. In short, insulating and sealing with the appropriate materials in the appropriate layers.

  7. plumb_bob | | #9

    Ha Ha he called me plump bob good one

    1. walta100 | | #11

      I apologize that is me being dyslexia I will edit it if you like your call Bob.


  8. GBA Editor
    Kiley Jacques | | #10

    Here are a handful of resources for insulating, sealing, and venting (or not) crawlspaces:

    Crawlspaces that Work

    Details for a Closed Crawlspace

    What’s the Best Way of Dealing With a Leaky Crawlspace?

    “In most areas of the U.S., sealed crawlspaces work much better than vented crawlspaces.”—Martin Holladay

    If you decide against venting, read: Building an Unvented Crawlspace

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