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

    <schemaVersion>X0305</schemaVersion>

    <documentType>4</documentType>

    <periodOfReport>2012-04-30</periodOfReport>

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

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001209469</rptOwnerCik>
            <rptOwnerName>RYAN JERRY E</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>6171 S. MARION AVENUE</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>TULSA</rptOwnerCity>
            <rptOwnerState>OK</rptOwnerState>
            <rptOwnerZipCode>74136</rptOwnerZipCode>
            <rptOwnerStateDescription></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>2012-04-30</value>
            </transactionDate>
            <transactionCoding>
                <transactionFormType>4</transactionFormType>
                <transactionCode>A</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionAmounts>
                <transactionShares>
                    <value>16</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>14888</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 outstanding RSUs as a consequence of a dividend paid on the Company's common stock on April 30, 2012.  The RSUs issued on April 30, 2012 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>2012-05-01</signatureDate>
    </ownerSignature>
</ownershipDocument>
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X0305
4
2012-04-30
0000105634
EMCOR GROUP INC
EME
0001209469
RYAN JERRY E
6171 S. MARION AVENUE
TULSA
OK
74136
1
0
0
0
Common Stock
2012-04-30
4
A
0
16
0
A
14888
D
Represents restricted stock units ("RSUs") issued in respect of outstanding RSUs as a consequence of a dividend paid on the Company's common stock on April 30, 2012.  The RSUs issued on April 30, 2012 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
2012-05-01