<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2013-04-30</periodOfReport>

    <issuer>
        <issuerCik>0000105634</issuerCik>
        <issuerName>EMCOR GROUP INC</issuerName>
        <issuerTradingSymbol>EME</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001451762</rptOwnerCik>
            <rptOwnerName>Laidley David H.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>1 PLACE VILLE MARIE</rptOwnerStreet1>
            <rptOwnerStreet2>SUITE 3000</rptOwnerStreet2>
            <rptOwnerCity>MONTREAL</rptOwnerCity>
            <rptOwnerState>A8</rptOwnerState>
            <rptOwnerZipCode>H3B 4T9</rptOwnerZipCode>
            <rptOwnerStateDescription>QUEBEC, CANADA</rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2013-04-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>29</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>24441</value>
                    <footnoteId id="F2"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Represents restricted stock units (&quot;RSUs&quot;) issued in respect of already outstanding RSUs as a consequence of a dividend paid on the Company's common stock on April 30, 2013.  The RSUs issued on April 30, 2013 are subject to the same vesting and forfeiture provisions as the RSUs in respect of which they have been issued.</footnote>
        <footnote id="F2">Includes shares issuable in respect of restricted stock units.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Sheldon I. Cammaker, Attorney-in-Fact</signatureName>
        <signatureDate>2013-05-01</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0306
4
2013-04-30
0000105634
EMCOR GROUP INC
EME
0001451762
Laidley David H.
1 PLACE VILLE MARIE
SUITE 3000
MONTREAL
A8
H3B 4T9
QUEBEC, CANADA
1
0
0
0
Common Stock
2013-04-30
4
A
0
29
0
A
24441
D
Represents restricted stock units ("RSUs") issued in respect of already outstanding RSUs as a consequence of a dividend paid on the Company's common stock on April 30, 2013.  The RSUs issued on April 30, 2013 are subject to the same vesting and forfeiture provisions as the RSUs in respect of which they have been issued.
Includes shares issuable in respect of restricted stock units.
Sheldon I. Cammaker, Attorney-in-Fact
2013-05-01