Geo­ther­mal not right for ev­ery space

Winnipeg Free Press - Section G - - HOMES - ARI MARANTZ

QWe are plan­ning to change a 300-square-foot at­tached garage to a home ad­di­tion, which will be a mu­d­room and en­trance. At this time, there is an ex­ist­ing ce­ment pad, which is in good con­di­tion. Do we need to re­move it to put in geo­ther­mal heat­ing? Is there any other type of heat­ing that we could place on the ce­ment floor? — Paulette Giesbrecht An­swer: While you have asked a good ques­tion about pos­si­ble heat­ing so­lu­tions for your planned ad­di­tion, you are some­what mis­guided on geo­ther­mal heat­ing. We will dis­cuss the dif­fer­ent pos­si­bil­i­ties for your sit­u­a­tion, while ex­plain­ing the geo­ther­mal-heat­ing con­fu­sion. Geo­ther­mal-heat­ing sys­tems are those that use the nat­u­ral ther­mal prop­er­ties of the Earth for a source of heat­ing and cool­ing. While the tech­ni­cal as­pects of the sys­tems are very com­plex and be­yond the scope of this col­umn to ex­plore, the ba­sic prin­ci­ples are quite sim­ple. To ex­plain this we must un­der­stand that the tem­per­a­tures of the Earth, deep down un­der­ground, are fairly con­sis­tent year-round. Be­cause of this, we can use the higher ground tem­per­a­tures, rel­a­tive to our cold win­ter am­bi­ent tem­per­a­tures, for a source of heat. In the hot sum­mer, we can use the cooler tem­per­a­tures un­der­ground to op­er­ate air-con­di­tion­ing sys­tems for our homes. In sim­pler terms, for the heat­ing sea­son, we ex­tract heat from the ground and in the sum­mer, we shed heat to the same lo­ca­tion. Most geo­ther­mal sys­tems in our re­gion in­cor­po­rate a se­ries of long, plas­tic pipes that are buried deep in the soil be­neath our yards. Th­ese pipes are typ­i­cally filled with a liq­uid that is used as a medium for heat trans­fer. This liq­uid is cir­cu­lated through the pipes to a geo­ther­mal unit in­side the home, which has a heat ex­changer and air-han­dling sys­tem to blow the heated or cooled air through­out a home. To in­stall this sys­tem only for your small ad­di­tion would be to­tally im­prac­ti­cal. To in­stall one for the en­tire heat­ing and cool­ing re­quire­ments of your home, when ren­o­vat­ing the ad­di­tion, may be pos­si­ble but quite costly. What you are likely re­fer­ring to is not a geo­ther­mal sys­tem, but an in-floor hy­dronic ra­di­ant-heat sys­tem. That type of in-floor heat­ing sys­tem is one that also uses plas­tic pipes filled with liq­uid for heat­ing, but that is where the sim­i­lar­ity ends. Many of those sys­tems are em­bed­ded in con­crete or mor­tar and use a stan­dard boiler and cir­cu­la­tion pump for heat dis­tri­bu­tion. The boiler heats the liq­uid in the pipes, which flows through the lengthy pipes, turn­ing the con­crete floor slab into a gi­ant ra­di­ant heat­ing plat­form. That type of sys­tem would be prac­ti­cal for the ad­di­tion you are plan­ning, be­cause of the use of the ex­ist­ing con­crete slab on grade. The two main draw­backs would be the over­all cost of the sys­tem in­stal­la­tion and the loss of heat through the slab to the soil be­low. In­stalling a long se­ries of PEX pipes, in­clud­ing a man­i­fold, and em­bed­ding them in a mor­tar bed over your ex­ist­ing slab may be a costly ven­ture. Also, the cost of a new boiler and cir­cu­la­tion pump, as well as the other var­i­ous con­trols and safety de­vices re­quired, may make this type of sys­tem too ex­pen­sive for such a small space. The costs to run the sys­tem, as de­scribed, would also be more costly than nec­es­sary due to loss of heat to the soil, due to a lack of proper ther­mal in­su­la­tion. To pro­tect against the heat loss, the old slab would have to be bro­ken up and re­moved, to al­low in­stal­la­tion of rigid in­su­la­tion be­neath a pro­posed new slab. There are two fairly easy and in­ex­pen­sive meth­ods to heat your new ad­di­tion, other than those al­ready dis­cussed. The first would be to in­stall warm- and re­turn-air ducts and reg­is­ters from the ex­ist­ing forced-air heat­ing sys­tem from the home. The dif­fi­culty would de­pend upon ac­cess to the ex­ist­ing duct­ing, and whether the cur­rent fur­nace had the ca­pac­ity to heat the ad­di­tional 300 square feet of con­di­tioned space. If not, an up­grade to a more ef­fi­cient and larger-ca­pac­ity fur­nace would be needed. The other, even sim­pler op­tion would be to in­stall elec­tric base­board heaters for the new area. The size of your over­all elec­tri­cal ser­vice may limit this sec­ond op­tion, but it is nor­mally the eas­i­est and least costly choice. Un­for­tu­nately, there is one ma­jor down­side to th­ese con­ven­tional heat­ing sys­tems. The con­crete floor slab will al­ways be cool or cold to walk on with ei­ther an elec­tric base­board or forced-air heat­ing op­tion. This is due to di­rect con­tact with the cold soil be­neath the floor. Build­ing a wooden sub­floor, with proper in­su­la­tion, may help limit this prob­lem, but may still yield a cold floor due to the lack of heat be­neath. A bet­ter so­lu­tion to this is­sue may be in­stal­la­tion of an elec­tric-grid, in-floor heat­ing sys­tem. Th­ese sys­tems are typ­i­cally in­stalled cov­ered in a thin mor­tar layer, which acts as a ra­di­antheat source, warm­ing the floor and the room above. The ben­e­fit of this sys­tem is the ini­tial cost of in­stal­la­tion would be much less than the hy­dronic ver­sion, due to the lack of pip­ing and a costly boiler. A spe­cial­ized GFCI-pro­tected ther­mo­stat and proper cir­cuit break­ers in­stalled in your elec­tri­cal panel would be re­quired, in­stead. You would still have the prob­lem of heat loss through the ground, but that could be min­i­mized by in­stal­la­tion of a layer of in­su­la­tion over the ex­ist­ing slab and con­struc­tion of a sub­floor over the elec­tric ra­di­ant sys­tem, if there is enough head­room. Con­fus­ing a ground source geo­ther­mal heat­ing sys­tem with an in-floor ra­di­ant hy­dronic one is an hon­est mis­take. Un­for­tu­nately, nei­ther is likely cost-ef­fec­tive for the small ad­di­tion you have planned, so al­ter­na­tive meth­ods de­scribed above should be ex­plored be­fore pro­ceed­ing with your ren­o­va­tions. Ari Marantz is the owner of Trained Eye Home In­spec­tion Ltd. and the past pres­i­dent of the Canadian As­so­ci­a­tion of Home & Prop­erty In­spec­tors — Man­i­toba (cahpi.mb.ca). Ques­tions can be emailed to the ad­dress be­low. Ari can be reached at 204-291-5358 or check out

his web­site at trained­eye.ca.

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