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26 Answers

Heat loss calcs to cfm?

What is the best way to translate heat loss calculations to CFM needs per room?

I have used HVAC-Calc Residential to identify the heat loss for finishing my basement and now need to turn those calcs into cfm to determine duct sizing.

For the HVAC-Calc experts, the "HVAC-Calc CFM report" does not seem to be helpful in this situation as it wants me to designate the CFM of the equipement for the house. The furnace that will service this zone also services the rest of the house.

Asked By BobTheWeekendWarrior | Jan 3 18
4 Answers

We're having a ventless dryer delivered next weekend. How should we seal the old vent?

The laundry room is finished; I'm not looking forward to the idea of cutting out the drywall to be able to remove the screws so I can pull the vent hood out from the outside. Any suggestions? Or should I just do the drywall work? Should I leave the duct alone and seal at the indoor end in case there's ever reason to go back to a vented dryer?

Asked By Calum Wilde | Jan 7 18
1 Answer

Condensing appliance exhaust heat recovery?

[I tried to add a comment to but it flagged this as spam and I could not.]

I'm looking for products or methods used to preform exhaust air to intake air heat recovery for a condensing furnace or boiler.

Asked By David Hollman | Jan 7 18
4 Answers

Recommendations for minisplit? Climate Zone 6 report included

This is a follow up on an earlier post. I have attached the engineer's report I received along with plans. What I don't know is what the ideal location for heads and zones on the mini split should be. Any recommendations?

The report shows a furnace but please disregard we are trying to use a mini split. We are also using an hrv for the ventilation.

Asked By User-6925805 | Jan 5 18
6 Answers

How to deal with condensation in a cold attic furnace?

I am a HERS Rater and one of my builders said he received callbacks 15 homeowners on completed homes with 95% furnaces in unconditioned (cold) attics this past week. While I suggested they may have been not able to perform due to extreme cold conditions, we then got onto him going back to 80% furnaces, which I do not want to encourage. So here is my question:

Condensate line in attic furnaces - how to do them right without building a room or spray foaming the roof system. To keep them outside thermal envelope but not have a problem with condensate.

Asked By Thomas Barnes | Jan 4 18
1 Answer

Controlling airflow at ventilation system endpoints

If you're trying to get specific airflow amounts at the endpoints for an ERV-based ventilation system, how do you go about doing this? Are dampers commonly used? Just on the supply registers or also on the exhaust intakes?

Or do folks generally try only to measure/control total supply airflow and total exhaust airflow, and then just distribute the endpoints in some reasonable fashion (e.g. one supply for bedrooms or offices, two or three supplies for a great room, etc.)?

Asked By William Costello | Jan 2 18
2 Answers

K-factor and airflow measurement

Can anyone shed light on how to determine your "K-factor" at a given point in a duct? Reason I ask ...

Asked By William Costello | Jan 2 18
5 Answers

Ventilation system registers - wall, ceiling, or floor?

We're going to do a walk through with our HVAC contractor next week to determine endpoint locations and duct layout for our ERV-based ventilation system. Most of what I've read indicates that both the fresh air supply vents and the return grilles should be located high up on the wall or on the ceiling. But some preliminary back and forth has me thinking that my HVAC contractor would like to put the supplies on the floor. Simpler for them I guess. From a comfort perspective, seems like the high wall or ceiling location would be preferable.

Asked By William Costello | Dec 30 17
5 Answers

HRV/ERV with two furnaces

I am looking to install a ERV in a home that has two furnaces. One furnace serves the basement and 1st floor (furnace #1) and the other serves the second floor (Furnace #2).

Square footages are approximately:
1500 first floor
2000 second floor
1500 basement

Climate zone 5 (Chicago)

For cost reasons I would like to install only one ERV system for the entire property. Also for cost reasons I would like to utilize the forced air system(s) duct work.

What does the community think about hooking up the ERV as follows:

Asked By Ryan Ohman | Dec 29 17
9 Answers

Are cupolas worth considering on a well insulated home for ventilation?

Are cupolas worth considering on a well insulated home for ventilation in the summer? In zone 5a there are some months where the day time requires some A/C and the night does not. A whole-house exchange of air would be nice around 8 o'clock at night, when the temps outside drop.

The idea would be to open up the cupola along with the first floor windows and allow the stack effect to exhaust the air. I guess it's the same idea as the whole house fan that pulls all the air out of the house and into the attic. We had one in our old house and it never seemed to work as good as the theory.

Asked By russell berenson | Dec 9 13
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