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Chemist1961 11-30-2009 07:44 PM

Approaching need for HRV
I have begun insulating my attic and sealing air loss along my rim joist and behind baseboards in my 35 year old home. Before and after Energy audits with blower door tests show I have already reduced my air change rate from 6.5 to 3.5 per hour. :eek:I have also blown in the attic to R50 and sealed the hatch.

My concern is that I still had planned to spray foam under my remaining baseboards on approx 1/3 of the upper and lower levels of the home as well as strip my stucco upper level to tar paper and re wrap and add R10 exterior insulation to the outside stucco portion, which makes up roughly 60 % of my exterior wall surface. In addition I still plan to insulate my basement walls and had planned to use foil faced foam.

I am wondering about how to retrofit an HRV system and how to reduce draft and insulate for up to -30 degree winter temps and +100 summer WITHOUT compromising the proper air flow in the house.

yuri 11-30-2009 08:50 PM

These are the best units in my opinion:

I have a 155MAX.
There is no "specific" "proper" air flow. You are however making your house extremely airtight and you will need a fair bit of fresh air to get rid of odors/ give you fresh oxygen etc. Read the installation info of this Lennox unit for the 3 types of dedicated systems and see which works for you. They are made by Lifebreath for Lennox. I would go with the programmable wall units (real Sweet technology!). Stay away from the ECM motor type as I hear they have noise problems with the motors and contractors are removing them and going with the conventional type. Until they redesign the motors they are not recommended. Not that much more efficient anyway. Send me a private message and I can help you more as this will clog up the board with details that most people won't understand.

The HRV3 is the latest/greatest offering:
You can save those pdf files to your computer.
You should get it professionally installed by someone who has done LOTS of them and has a proper magnehlic gauge to balance it properly or it is a waste of time and $$. I do a lot of this type of work.
Good Luck

beenthere 12-01-2009 04:52 AM

Is that ACH50 3.5???

Chemist1961 12-01-2009 09:24 AM

Yes I believe that it was natural air change rate 6.5 hour at 50 pa.., now reduced to approx 3.5 after sealing the rim joist, some baseboard ares installing weighted damper type vent hoods, etc. I'm stunned by the change, but I want to proceed with caution

beenthere 12-01-2009 03:00 PM

3.5 is very low. Nice job!

Get that HRV installed soon though.

creamaster 12-01-2009 06:38 PM

Im in the same boat, my home energy audit showed that our 45 year old ranch is too air tight after Ive done all new windows, doors , and attic insulation. The technician was surprised as he lives in the same neighborhood in the same type of house and his is leaky. Not sure on my exchange rate but it says my shell leakage is 1700 CFM50 and the industry standard is 1870.31 CFM50 for my house. Can that be converted to ACH? The technician said it means the house is too airtight but the ACH would be nice to know.

They quoted me $2,500 for a Lennox HRV. Im thinking of buying a cheaper one and getting a magnehlic gauge to balance it myself.

Question..Can the HRV simply be ducted into the basement for a ranch house, both supply and return as long as it is balanced?

beenthere 12-01-2009 06:50 PM


Originally Posted by creamaster (Post 359962)

Question..Can the HRV simply be ducted into the basement for a ranch house, both supply and return as long as it is balanced?

Not if you want it to do any good.

Should know the total volume of your house to do the conversion from ACH50 to ACH for your home under normal conditions.

Chemist1961 12-01-2009 09:21 PM

Thanks BT for the compliments and the advice as always. I was fairly diligent but I still surprised myself with these results but as stated I am now in a quandry as to how to proceed as I have several target areas including bulkheads against my garage wall that were never properly sealed and now I'm not sure how to handle them without going to a lower ACH rating.

beenthere 12-02-2009 04:00 AM

Is your heating system hot air, or hot water.
If its a hot air duct system. Use the hot airs duct system to remove stale and distribute fresh air. Tap both the stale and fresh air of the HRV into the return duct. And wire it to bring on the central systems blower when the HRV runs.

If hot water.
One way. Is to install the fresh air supply in a common hallway. And the stale air in the basement(providing that there is undercut on the basement door).
This gives an ok mixing of fresh air to the whole house. A little lacking to the bedrooms at night. If those doors aren't under cut.

Chemist1961 12-02-2009 07:09 AM

The system is original forced air, gas with a new HE furnace last Jan. Given my sealing results and upgrade to R32 insulation on the rim joist I am really looking forward to a plummeting gas bill. Consumption was down over 30% in Feb before the rim joist was done so this has been a huge win. I expect my actual furnace payback after gov't rebates (for energy saving devices) and gas savings will be under 4 years so the savings can be put into an HRV.
On top of that I will get a BONUS grant for my air sealing efforts hitting over 20% above target , plus extra grants for my attic and rim joist of over materials since I completed the work myself above the benchmark. Its like Christmas bonus time for my year long efforts and more grant money on the table along with future gas savings when I insulate the basement walls
Couple more questions:
How big a intake and exhaust opening will I need to core ( I think I have as big as a 4.5" core)thru my brick for a typical HRV and how far away from the furnace intake/ exhaust would be normal... I want to plan for future piping requirements as I insulate and rewire my furnace/laundry room walls.
Will the HRV install conflict with my General humidifier which is currently installed on the cold return or should the humidifier be moved to the hot side and the intake duct be used for the HRV?
Can I install the HRV myself with proper guidance or should it be left to a pro

beenthere 12-02-2009 01:23 PM

The HRV's intake and exhaust sizes, will depend on the unit you get. 6" and 8" are the most common for residential.

Code(USA)requires the intake of the HRV be a min of 10' from the furnace exhaust.

You probably don't need the humidifier anymore with your house getting that tight.
But, if you want to keep it just incase. I would install the HRV stale and fresh air lines in the horizontal trunk, if the humidifier is in the way on the vertical return drop.

A competent person can install one.
So is a contractor you hire competent enough or not?
Are you(not meant to be insulting)? You have to decide that yourself.
Generally. If you can follow directions. without taking unapproved short cuts. You can install one.

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