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  1. #1
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    Default Insulating crawl space...home inspector said no

    I've read the similar posts on this subject, but didn't want to hijack them. We bought our '48 split level about 6 yrs ago. The main floor is over an uninsulated crawl space. The crawl space has two exterior vents, and vented vented doors to a downstairs family room.

    When we bought the house the home inspector said not to insulate the crawl space. I cant remember his exact reasoning, but I believe it had to do with the heater needs to pull air in to be efficient. After the first winter without being able to use the downstairs family room, because it was so drafty, I finally put insulation in the vents and on the vented doors. This did help....although still cold.

    The main concern is the main floor....it seems cold all the time, so I was thinking I should insulate the floor. From reading the other posts, I'm thinking this will be ok. What size insulation should I use...were in South Eastern, PA. I saw something in one of the other posts about moistue control, should this be a concern in the summer?

  2. #2
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    Default Re: Insulating crawl space...home inspector said no

    try a spray foam contractor its easier

  3. #3
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    Default Re: Insulating crawl space...home inspector said no

    Scribe ... perhaps it's me but .... I'm not quite following the description regarding a vented door to the downstairs family room and how it's connected to the crawl space.

    Also is the family room over a crawl space?

    What is in the crawl space a dirt floor and what is the foundation setup?

    Also can you describe your heating system?

    Perhaps you could include some photos.

  4. #4
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    Default Re: Insulating crawl space...home inspector said no

    Don't have any photos handy that would explain layout, so I put this quick picture together to give you an idea of the layout. The green in the picture is the surrounding grade of the property. As well as an example of the venterd doors, which go across the family room as an entrace to the crawl space beneath the living room/main floor.

    The heating system is gas forced air unit. The house is built on a cinder block foundation, with a rough concrete floor in the crawl space.

    Think that answers your questions. If any other information would help, please let me know.
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  5. #5
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    Default Re: Insulating crawl space...home inspector said no

    Quote Originally Posted by Scribe View Post
    Don't have any photos handy that would explain layout, so I put this quick picture together to give you an idea of the layout. The green in the picture is the surrounding grade of the property. As well as an example of the venterd doors, which go across the family room as an entrace to the crawl space beneath the living room/main floor.

    The heating system is gas forced air unit. The house is built on a cinder block foundation, with a rough concrete floor in the crawl space.

    Think that answers your questions. If any other information would help, please let me know.
    Great stuff ... I was thinking that might be the way it was ... just had to be certain.

    Is the furnace system located in the crawl space ?

    Is the "vent" that's in the crawl space simply opened to outside ?

  6. #6
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    Default Re: Insulating crawl space...home inspector said no

    Here is a diagram of the layout of the bottom floor. The crawl space would be all to the right. The HVAC and Water Heater are in the utility room across the hall from the Family Room.

    The vent in the crawl space does go right outside.
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  7. #7
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    Default Re: Insulating crawl space...home inspector said no

    Yep ... I was suspecting this would be the case and I put down some thoughts.

    Unfortunately you currently have a less than desirable situation that frankly makes me scratch my head as to why it was done this way.

    If you excuse my long winded explanation it may explain what's going on.



    COMBUSTION FRESH AIR SUPPLY

    FURNACES & BOILERS

    A combustion furnace ,water heater or boiler (gas, oil, coal or wood) requires air to burn and air to maintain a proper draft in the chimney.

    The national gas code is the strictest code in addressing this problem because gas burns with a cooler chimney temperature than other fuels and can have more trouble creating a safe draft. The gas code requires 1 sq. in. of free open duct (taking into account the reduction of air flow through bug screens) for every 5,000 BTU capacity of the total of all the gas burning appliances (furnace and water heater). In many modern houses this means 6 to 8 in. diameter open ducts in the basement. The result may be fine for the furnace but will over ventilate the house and dry it out to the point where it is impossible to humidify not to mention the arctic temperatures on the basement floor.


    Traditional furnace rooms are nothing more than a partition designed to hide an ugly furnace. They are neither sealed nor insulated, and they obtain combustion air from the house.

    The most common technique in basement installations, is to use an insulated duct to dump air a few inches off the floor next to the combustion intake. Because the duct comes from the joist area down to the floor it must be heavily insulated to minimize condensation.

    Many houses were supplied with ventilation ducts that looped down and then back up and then back down again along the basement wall, to create something similar to a plumbing trap. Others had the duct terminate in a sort of bucket, again to try to create a "trap" sort of arrangement. Both of these worked fairly well, except when the wind blew, still chilling the basement part of the time.

    This effectively provides combustion air and sufficient draft air to minimize the effect of exhaust fans on the furnace chimney. However, this open duct bypasses a controlled ventilation system, particularly a heat recovery ventilator, and makes for a permanently cold basement floor.

    The problem is that the furnace needs this large air supply while it is heating, but that most of the time this unrestricted air supply is simply over ventilating the house.

    The worst but valiant effort was the sealed furnace rooms.


    A SEALED FURNACE ROOM & WHY IS IT NOT RECOMMENDED


    Sealing off the drafty leaks in a house and introducing a system for controlled ventilation means that exhaust fans and chimneys have to compete with each other for air -- which leads to complex and sometimes unpredictable air currents. A sealed furnace room was conceived as a way to isolate the two air-supply problems -- combustion and chimney draft air inside the furnace room, fresh air and stale exhaust inside the house.

    With this isolated room, a gas leak would not be detected until it was already explosive. You would never smell it because this room was completely isolated from the air of the house. To safeguard against this, a lot of fresh air ventilation into this room is required. This tends to drop the temperature of this room so low, sometimes below freezing, that the chimney can constantly condense or even freeze.

    Meanwhile two technological developments were simply made to overcome those problems.

    First was the advent of the sealed combustion furnaces. This took the same isolation concept, but built it right into the furnace . Outdoor air comes directly into the furnace and then back out through the flue. These units use no household air and are not in competition with any other exhausts in the house. That is the ultimate solution, but can be very expensive, so not for everyone.

    Second was the development of the Hoyme Damper. (link)
    This is a motorized damper that is interlocked to the furnace so that it opens when the furnace needs air and closes when it does not.
    The Hoyme damper is the only one I am aware of that is approved by the gas code as fail safe and brings basement air control to ordinary furnaces and boilers. though that would have to be determined in your area.

    So with these two very good options, don't try to isolate the furnace in some kind of sealed chamber. You will be causing more problems than you solve, not to mention that there are now much simpler proven solutions.

    So I guess a couple of solutions would be to replace the furnace with a direct venting type or relocate the intake air vent to the furnace room area. This way you can close off that opening to the out side and you will be a lot more comfortable.

    Hope this helps.

  8. #8
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    Default Re: Insulating crawl space...home inspector said no

    Canuk,
    Thank you very much for the information. So would it be ok to keep the vented doors in the family room insulated like they are now, anyway, and put a vent into the utility room, that can access the crawlspace and therefor the vents to the outside and bring fresh air in?

    The main concern though is the living room above the crawl space, and wether it's ok or not to insulate the roof of the crawl space which would be the floor of the living room.

    Sorry if this was part of the explanation that I missed somehow.

  9. #9
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    Default Re: Insulating crawl space...home inspector said no

    Quote Originally Posted by Scribe View Post
    So would it be ok to keep the vented doors in the family room insulated like they are now, anyway, and put a vent into the utility room, that can access the crawlspace and therefor the vents to the outside and bring fresh air in?
    Well sort of... In a leaky house with the furnace in an open basement this isn't really a problem.... your situation is a vent that's simply open to outside is likely being used to provide extra combustion air for the furnace ... and hot water tank if it's not electric.

    Someone likely felt you require this extra combustion air source that's why the opening to the outside. Frankly I don't understand why it was done that particular way instead of having the ducting at the location of the HVAC .
    The problem is that's it's located in the crawl space across the room from the furnace and it's freezing the entire lower level.

    Either you leave things as is and freeze in the lower family room.
    Or possibly run ducting from the vent in the crawl space all the way to the HVAC location. This will help somewhat but it will still be cool around the HVAC area.

    Another way may be to close off that existing vent in the crawl space and provide a new vent to outside where the furnace currently is.

    However ... this will still leave cold outside air being pumped into the lower area all the time.... as I mentioned earlier... unless you were to install a damper like the Hoyme damper.

    Or...consult a furnace expert to evaluate if your furnace has a sufficient air supply.... in which case it may be dertermined you don't need this vent at all and all your problems would be solved.

    The ultimate option would be to replace the existing furnace with a direct vent high efficient furnace that would eliminate this need for extra combustion air.

    The main concern though is the living room above the crawl space, and wether it's ok or not to insulate the roof of the crawl space which would be the floor of the living room.
    The reason that your spaces are cold is simply you have an open hole to the outside just like leaving a window open. If you leave things as is .... insulate the heck out of the underside of the above floor.

    If you make the changes discussed then the vent to the outside wouldn't be flooding the crawl space with cold air and that issue would more likely be curred.

    Sorry if this was part of the explanation that I missed somehow.
    No worry ... I kinda went overboard with the information.

  10. #10
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    Default Re: Insulating crawl space...home inspector said no

    Canuk,
    I think replacing the HVAC will be something to do in the not to distant future. So until then, I think I'll insulate the floor and try more direct root from the vent to the HVAC....again thanks for all of your information it's much appreciated.

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