I just purchased a new Panasonic Whispergreen bathroom fan and I like the idea of having it on at low speed at all times. However, since our house is pretty new and has fairly tight construction, I'm concerned that this will create a vacuum condition inside the house and could interfere with the drafting of exhaust gasses from our furnace or water heater. In doing a little research, I found the Honeywell Y8150 fresh air ventilator. I was wondering if anyone has any experience with this, or if I really shouldn't be concerned about it, or is there a better option like a heat recovery ventillation system? I live in Minnesota, in case that matters. I also don't really want to spend $1000+ for a heat recovery ventilator, but if that is what I need, I'd like to know.
How many CFM is the exhaust fan on low.
Although expensive, HRV's can pay for themselves by not increasing your heating and cooling cost, compares to just a fresh air intake.
HRV's are not for make up air.
But are some times used for it.
I have this unit on mine and been happy with this. Reason I went with this instead of HRV is that I have an older home, no space for it, and fresh air was already tied into my return duct.
I just wanted to control the fresh air, rather than having it dump the cold fresh Minnesota air into the home all the time. MN code is that you need to have a fresh air pipe brought into the home and most likey it's next to the water heater. I did add this since the damper is closed at time, and needed make up air for the water heater.
The only thing I don't like about it is that I run my fan 24/7. When the damper opens at night, it brings in more cold air into the home. But I got a VisionPro IAQ on it's way I am going to wire that into the IAQ. The IAQ will allow me set it up to not allow fresh air in sleep mode (Night set back)
The low speed for this fan is configurable, and the chart says for my house I should set it at about 45 CFM.
HMM, yet another reason to get the IAQ! I just got a new heat pump installed and although I wanted an IAQ my HVAC installer said that Carrier recommended against it. Oh well. Maybe I'll upgrade down the road.
So, if I have a fresh air intake as per code (I'll check), is that going to be enough to keep up with the 45 CFM draw? I realize this probably depends on the size of the pipe coming in, but I guess I'm asking for an opinion based on standard practices.
At 45 CFM 24/7 you would be incresing your heat loss to 3402 btu's an hour at 70 ID and 0 OD temp, or 81,648 btu/s a day at those temps.
At 35 OD and 70 ID temp, 1701 btu's an hour, or 40,824 btu's a day.
Are you sure a HRV wouldn't be a good idea.
Wow, I didn't realize that it would increase heat loss that much! It makes sense though. Thanks for the numbers.
Now I have to decide if the additional $20/month that it would cost in heating is worth it for additional fresh air. Time to ask the wife!
Don't forget, if you have central A/C, it adds cooling load also.
Thanks mayguy for the experience advice, and thanks again to beenthere for crunching the numbers. At this point I think I'll hold off on this device and see what happens. BTW, I really like the whispergreen fan. It's very quiet and it actually keeps my mirror from fogging up in the morning.
I just got myself the new IAQ t-stat, and it's tied onto that. Nice thing about the IAQ vs the board that comes with the damper is that the IAQ will allow you to not allow the damper to open at night.
Also, beenthere did make a good point about the load. but this load is not there all the time.. The damper opens and closes as needed on the set up of the IAQ. (How many bedroom, CFM of fresh air, How many Sq ft the home is)
I've been happy with it so far. Today, I wanted more fresh air into the home, I set the timer on the t-stat for an hour.. So the damper is open for an hour.
This is also my dilemma. We have built an ICF house with 3400 sq feet. I currently have planned for an HRV unit but the HVAC installer recommends saving some money and using the Honeywell Fresh Air Ventilator. He also said that from what he has seen is that many people dont change the filters in the HRVs and the motors burn out after two years or so. Then the people dont even use the HRVS. Have you seen this? I am very concerned about fresh air in an ICF house. What do you think on this issue?
You are right about the HRV, I've seen units that the owners never cleaned, and didn't provide any fresh air, kinda like owners never cleaning their electronic air cleaner.
I have the Y8150 on my home, and I am pleased with it.Also, it's simple and quiet. I would of done the HRV, but I have no space for it.
HRV/ERVs, are like any other piece of equipment.
They need to be serviced on a regular basis.
If you clean the filter like you should. You save on your heating and cooling bill.
The effect of adding 45 cfm is misunderstood. A home already has some natural fresh air infiltration/exfiltration. The amount of natural depends on the outside temperature and wind velocity. At 10^F and 7 mph wind, the natural is close to blower door rating. A moderately tight 2,500 sqft. home(.2 air change per hour) leaks 75 cfm during average winter weather. How does adding 45 cfm of make-up air change the house? Experts find that adding air slows the infiltration and increases the exfiltration. The estimate is natural infiltration declines by half of the mechanical make-up air flow. The exfiltration increases by half of the make-up air value. So expect to have to heat an additional 23 cfm of cold air when the make-up air operates. The other important issue is to bring fresh air only when the home is occupied. This is useally less than 12 hours per day. The heating calculation is 23 cfm for 12 hours at the delta tee. This cuts the 80,000 btus down to 20,000 btus per day. This is about 8 therms NG a month during cold weather. During warm weather, natural infiltration declines to wind driven natural ventilation only because the inside/outside temperatures similar. I often find a home like above is getting as little as an air change in +24 hours during cooling season. So adding 45 cfm fresh make-up air to a home that breathes very little has more of an impact cold weather ventilation. Again only operate the make-up air when the home operated. The cost of cooling and dehumidification during the warmest month is $30 per month. 45 cfm of fresh make-up air for 12 hrs/day for the year may cost <$200 for the year, using make-up air without a HRV. An HRV would reduce this cost less than 40%. When large amounts of fresh air are required, HRVs are an ideal device.
Originally Posted by beenthere
My testing indicates it is best to follow ASHRAES recommendations of about 70 cfm of make-up air when occupied year around, as a minimum. If a home does not have moisture on the windows during cold weather, there is usually enough fresh air infiltration to not need fresh air.
During non-heating/non-cooling weather and without dehumidification, the properly ventilated home (air change in 4 hours) will have an interior moisture level (grains/dew point) slightly higher than outside. In green grass climates, +55%RH levels are unacceptable and dehumidification is suggested. I am attaching ASHRAE's suggestion for minimal fresh air. Regards TB
Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
Use +Merv 10 air filter. -Don't forget the "Golden Rule"