Dehumidifier and ERV questions for new Construction HVAC
Hi everyone,
I am in the process of building a new construction home in Houston and need help making decisions regarding the HVAC system. The house should have a fairly tight envelope with 2×6 construction and spray foam insulation. I am going with a Lennox system (XC21 condenser, EL296V furnace, ERV, PureAir purification system).
The HVAC contractor says the XC21 has a built-in dehumidifying ability and a separate dehumidifier is unnecessary. Houston is very humid most of the year. I am leaning toward installing the Lennox dehumidifier system, Humiditrol. Would installing the dehumidifier be overkill? Would having an independent dehumidifier save on energy costs (compared to using the condenser to dehumidify)?
My builder thinks the ERV is unnecessary, but I prefer to have a well ventilated house. I know Mr. Holladay says a fully ducted system is the best option. I believe the HVAC contractor wants to do an exhaust ducted-system. Is it a better option to have the fresh air from the ERV go through the purification system? Also, the HVAC contractor said ERV exhaust duct would be placed in the living area. I was under the impression that there should be multiple ducts placed in the bathrooms and utility room. If i only have one exhaust duct, I am planning on having humidity sensor exhaust fans installed.
Thanks for all the help,
Bobby
Replies
I think you need to find someone who knows what they're doing and who you trust to lay out the vent system. It sounds like your contractor wants to do the bare minimum, and you will have to watch him to be sure no "shortcuts" are made.
HRV separate ducted system
I just installed a separate ducted HRV system in my house and thought I'd share my observations/experience with you.
I installed a Fantech 3005R in my attic. For the runs that were in exterior walls, I went with the Zehnder Comfotube piping because I too used spray foam in the walls (mine were mostly 2x4s though) and I was concerned that the spray foam would squish the lines. However, I switched to the cheaper ComfoFlex tubing for the runs that were not in exterior walls. The Zehnder tubing is not cheap, but is very easy to work with/route around obstructions.
Note: when you use spray foam in the walls, it is very important to tie wires and flexible pipes down securely prior to spray foam--you don't want them to be pushed out of the wall cavity--it is a real pain to fix afterwards.
I ran exhaust lines to the kitchen (not the hood, but nearby), bathrooms, and basement laundry room. In retrospect, I should have ran exhaust lines to the two crawl spaces as well. In the bathrooms, I also placed boost switches that push the HRV to high speed for a period of time.
All of the three bedrooms, living room, dining room, and family rooms received supply lines.
I installed the HRV/HRV ducts myself and saved thousands. You don't need much in the way of tools to do this.
A final note: You HAVE to get a Manual J Load Calculation done to determine the size of the HVAC system. There are many online services for this. Most HVAC contractors use a rule of thumb/square feet to determine the right HVAC size and usually over-estimate the needed size in order to avoid callbacks. The Manual J calculations will tell you the number of CFM that each room needs. Don't pay extra for duct design--your HVAC contractor can correctly figure out the size of ducts needed for each room. My HVAC contractor could not believe the low CFM that the house needed (300 CFM) (fully filled wall cavities with spray foam), and would only install the ducts if he was absolved of responsibility for sizing. The house is perfectly comfortable, and the system recommended by the Manual J service was the smallest/cheapest one that the manufacturer made.
Good luck.