high humidity in my house

10 on and 50 off is your issue. Not enough run time to drop the RH.

Good question.

Let me clarify the question.

Ventilation will only reduce the humidity indoors if the absolute moisture content of the outside air is lower than the moisture content of the inside air. If the opposite is true, ventilation will increase the humidity indoors.

Relative humidity, as it names implies, is not a measure of absolute moisture content, it's a temperature-dependent measure. The easiest measure to use is dew point. So ventilation only helps reduce humidity when the dew point outside is lower than the dew point inside. In most of the US, in weather where you would be running air conditioning, the outdoor dew point is higher than the indoor dew point.

The reason I asked about the outdoor conditions is that dew point can be calculated from temperature and humidity. What matters is not the range over the course of the year, but at the instant you're running the ventilation.

69 return if the unit is cycling on temp too much it will never lower RH enough. You may need reheat but that is expensive to run a bigger 9thicker coil is better.

I asked this before: With the water and air temps you have it this coil dumping a lot of water? It should be, and is it dumping the water outside the house?

In my experience I find that if HRV vents are at ground level (say if the HRV is in a basement) all they are doing in the summer is bringing in high humidity ground level humidity that defeats the AC system. Where I've found such systems I've asked the customers to turn off their HRVs anytime the outdoor temperature is above 50 degrees and to use them only when needed and only for as long as needed. They are intended to help control humidity and provide some heat exchange for fresh air make-up. However, in regions with high summer humidity they can easily over-ride conventional AC equipment and introduce high humidity air 24/7 if left running.

I think that where people get confused is that HRVs — or air conditioners without condensation, or shade, or whatever — do not change the actual moisture content of a volume of air — measured most conveniently by the dew point. Relative humidity is the relationship between the dew point — at which temperature the air mass holds as much moisture as it can without condensing — and the sensible air temperature, as measured by a normal thermometer. If you lower the sensible temperature, the relative humidity increases. Raise it, and the relative humidity decreases.

The only way you can lower the relative humidity at a given sensible temperature is to cool the air enough to lower it below the dew point, at which some of the moisture will condense out, and then warm it back up to where you want it.