How to be sure HRV sys­tem is up to par

Winnipeg Free Press - Section G - - HOMES -

QUES­TION: I am mov­ing into a new home and have or­dered an HRV sys­tem. You had stated in a pre­vi­ous news­pa­per ar­ti­cle many tech­ni­cians are not knowl­edge­able in in­stalling th­ese sys­tems. What should I look for when I do the new-home in­spec­tion? Thank you, WM

AN­SWER: Your ques­tion is timely as I re­cently in­spected two newly built homes by the same builder with dif­fer­ent HRV in­stal­la­tions, one cor­rect and one not. I will of­fer some guid­ance on what to look for on the unit in your home.

I am as­sum­ing the new-home in­spec­tion you’re talk­ing about is the walk­through with the builder’s rep­re­senta- tive prior to oc­cu­pancy. This is not a true in­spec­tion since you’re only asked to iden­tify any is­sues you know about. You’re not likely ed­u­cated in what to look for, other than cos­metic or ob­vi­ous de­fects. Ideally, you could have had a CAHPI in­spec­tor ac­com­pany you on a full in­spec­tion prior to this point, but that was not likely done.

The prob­lem with your in­spec­tion is not only the lim­i­ta­tion on your knowl­edge, but the lim­ited time given to you by the builder’s rep­re­sen­ta­tive and the need to iden­tify items without prior ac­cess. How­ever, I do com­mend you on seek­ing ad­vice on this is­sue so you are bet­ter pre­pared for your in­spec­tion.

As for eval­u­a­tion of your HRV, I will try to pro­vide a crash course on what to look for on your walk-through.

Firstly, you should en­sure the duct­ing con­nected to the HRV unit is go­ing to the right lo­ca­tions. While this may seem rather com­pli­cated, it can be sim­pli­fied con­sid­er­ably by looking for mark­ings or stick­ers on the HRV unit it­self. There will ei­ther be a schematic draw­ing, show­ing which ducts should be con­nected to var­i­ous ar­eas, or la­bels di­rectly be­side the ducts where they con­nect to the box.

There should be two solid metal ducts con­nected to the stale air com­ing from the house and the fresh air to the house con­nec­tions. The fresh-air duct should be con­nected to the re­turn-air duct­ing on the fur­nace and the stale air to duct­ing com­ing from the bath­rooms and other ar­eas of the house.

The next two con­nec­tions should be to in­su­lated duct­ing, which ter­mi­nates at hoods out­side the house. One will be for the fresh-air in­take and the other will be for ex­haust air. Th­ese vent hoods should be eas­ily vis­i­ble on the ex­te­rior of the house walls or foun­da­tion and of­ten have screens or grates in­te­gral to pre­vent pest in­tru­sion. If th­ese ducts ap­pear to be in the cor­rect lo­ca­tion, which is not nor­mally a prob­lem in most in­stal­la­tions, you can move on to the next step.

The next item to check is the con­trol de­vice for the HRV. This is nor­mally lo­cated in a hall­way or part of the main liv­ing area in the home and usu­ally be­side the ther­mo­stat for the HVAC sys­tems. There are sev­eral dif­fer­ent styles of con­trols, but most have a man­ual por­tion of the con­trol and a hu­midistatic por­tion.

The HRV can also be man­u­ally ac­ti­vated with switches in the bath­rooms. This as­pect re­places the older-style ex­haust fans and can be ac­ti­vated much the same way as in older homes. Again, th­ese are most of­ten work­ing fine in most new-home in­stal­la­tions.

The main prob­lem seems to be with the hu­midistatic con­trols. HRVs are de­signed to con­trol ex­ces­sive hu­mid­ity in homes by ex­haust­ing stale, moist house air and re­plac­ing it with dry, fresh out­side air. This not only re­moves pol­lu­tants from the liv­ing space caused by cook­ing, heat­ing and other hu­man fac­tors, but also elim­i­nates a lot of the mois­ture pro­duced from th­ese ac­tiv­i­ties.

This can be done man­u­ally by turn­ing the HRV on con­tin­u­ously, us­ing the main con­trol or bath­room switches, but may keep the unit run­ning too long, or not long enough. The hu­midi­s­tat on the main con­trol should be ad­justable to en­gage the HRV only when the rel­a­tive hu­mid­ity (RH) in the home sur­passes a cer­tain level. That level can also be ad­justed to ac­com­mo­date changes in weather and cli­matic con­di­tions. If that part of the con­trol is not func­tional, then the HRV is only a more en­er­gy­ef­fi­cient ver­sion of an ex­haust fan and not be­ing used to its max­i­mum po­ten­tial.

To check if it is work­ing, the HRV should come on au­to­mat­i­cally when the RH set­tings are turned down be­low the nor­mal range without en­gag­ing any other switches or con­trols. It should also shut off when the hu­midi­s­tat is fur­ther ad­justed above the RH in the home and both lev­els are nor­mally noted by a small click when the con­trol is ro­tated be­yond that thresh­old.

The fi­nal item to check is whether the HRV con­trols are cross-con­nected with the fur­nace fan. This is im­por­tant to pro­vide max­i­mum ven­ti­la­tion, es­pe­cially in some of to­day’s larger homes. The fans in­te­gral with the HRV are quite small, and the fur­nace fan can be of ma­jor as­sis­tance to pro­vide ef­fec­tive air cir­cu­la­tion when it is used in com­bi­na­tion with the HRV.

This can be checked sim­ply by lis­ten­ing to the fur­nace while the HRV is man­u­ally en­gaged. There may be dif­fer­ent set­tings on the con­trols to turn this func­tion on or off, so be care­ful not to jump to con­clu­sions if it doesn’t work when first at­tempted.

In the last few years, I’ve seen many HRV units im­prop­erly in­stalled or not func­tion­ing prop­erly. Lately, most of the prob­lems have been non-func­tion­ing hu­midistatic con­trols, but other items may also be a con­cern. As with any ap­pli­ance, HRVs re­quire reg­u­lar main­te­nance, which in­cludes clean­ing fil­ters and the core as per man­u­fac­turer’s in­struc­tions.

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