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rdurina
Ventilation: Balanced vs Supply

I had an energy audit performed and they recommend attic insulation and sealing, but since the house is too tight, they recommend a fresh air ventilation system.

I am concerned that any energy saving for insulation and sealing will be offset by the increased operation costs for the ventilation.

The contractor also recommends a supply only ventilation system. While the cost is about 1/2 of a heat recovery or energy recovery ventilator I am concerned that it will cause issues since the stale air is not being exhausted and I am curious if there are increased energy costs since the fresh air is being dumped directly into my HVAC.

I live in New Jersey and have forced hot air\central air conditioning. Either ventilation system will be connected directly to the hvac.

Any feedback on the energy costs or the comparison of a supply versus balanced (HRV\ERV) ventilation system ?

canuk
Re: Ventilation: Balanced vs Supply

Hmmm--- a supply only ???

The whole idea of the HRV is to provide a contolled air exchange for proper indoor air quality. The method you mention is not providing any air exchange.

As for cost of operating a HRV --- generally less than a dollar a day --- depending on size of unit , how often it's used , etc..

canuk
Re: Ventilation: Balanced vs Supply
Sten
Re: Ventilation: Balanced vs Supply

Some Commercial Roof Top Units have what's called an Economiser, it has a damper that opens on days when it's about 55-60 degrees but is warm enough inside the building to have the A/C on. This way you get whats called free air, it's run by an outside temp control that's mounter in the unit, it just bypasses the condenser and uses the same blower motor, sounds like he might be talking of something similar.
Good Luck!!!

Sten
Re: Ventilation: Balanced vs Supply

Hey Canuck, nice links, thanks!!! :D:)

rdesigns
Re: Ventilation: Balanced vs Supply

Houses can't be too tight, but they can be under-ventilated.

What you need is a controllable way to ventilate your tight house.

The best way, in the long run, is to use an HRV system.

This balances intake with exhaust, while at the same time, rcovering about half of the energy that would otherwise be wasted.

There is no need to run the HRV all thru the day. The systems come with timers you set to match your life pattern.

RJordan
Re: Ventilation: Balanced vs Supply

Lucky you to have a tight house. As rdesigns said, houses can only be under ventilated. I disagree with canuk that supply only ventilation doesn't provide any exchange. It does through all the myriad holes in the building. The building is pressurized by the fan however, driving heated air into the walls. This air may carry moisture where it can condense on the cold outside plywood. In your NJ climate you should use exhaust only ventilation. This will typically be a high quality, quiet, bath fan that is exhausted to the outside. It brings in air through the leaks in the building shell. Since you are bringing cold air into a warmer space, there wouldn't be condensation. However, you could be bringing in dust and pollen. The auditor should have the knowledge of how to calculate the size of fan and the necessary run time.

I read that the cost of the heat lost by exhaust only ventilation is about the same as the cost to run an HRV. The HRV is the better way to go, but the system does cost more. It will filter the air and conserves the heat in the building.

Timothy Miller
Re: Ventilation: Balanced vs Supply

Howdy you can have too tight of a sealed home . The # of times an hour that the air is changed in the home is the issue if not enough air exchanges then adding the exchange equipment increases it to a safe level. Consider the energy costs when making your choices as capturing the heat out before exhausting the air saves heating $. This need for air exchanges is is mostly for the winter time. In the other months simply cracking a few windows exchanges the air. If pollen an issue then install a hepa filter into the HVAC....

canuk
Re: Ventilation: Balanced vs Supply
RJordan wrote:

Lucky you to have a tight house. As rdesigns said, houses can only be under ventilated. I disagree with canuk that supply only ventilation doesn't provide any exchange. It does through all the myriad holes in the building. The building is pressurized by the fan however, driving heated air into the walls. This air may carry moisture where it can condense on the cold outside plywood. In your NJ climate you should use exhaust only ventilation. This will typically be a high quality, quiet, bath fan that is exhausted to the outside. It brings in air through the leaks in the building shell. Since you are bringing cold air into a warmer space, there wouldn't be condensation. However, you could be bringing in dust and pollen. The auditor should have the knowledge of how to calculate the size of fan and the necessary run time.

I read that the cost of the heat lost by exhaust only ventilation is about the same as the cost to run an HRV. The HRV is the better way to go, but the system does cost more. It will filter the air and conserves the heat in the building.

No sir ------- that thinking of relying on air exchange through cracks and gaps is and has been proved to be an incorrect assumption.
Current data from research has proven that a mechanical method of removing and supplying the same amount of air is the only proper method of air exchange --- such as the HRV.

RJordan
Re: Ventilation: Balanced vs Supply

Whether it would work depends on how leaky the house is. In a really tight house, probably not. If it wouldn't work, how would a bath fan work or a kitchen exhaust fan or a dryer? They all need to have air come in to make up for what they exhaust. There are "smart holes" that allow air to come in, like a Fresh 80.
Certainly the HRV will provide the best air quality.

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