Replies

1. 
   charlie_sullivan | Aug 03, 2021 06:45pm | #1

   It's problematic in many ways to install a refrigerant line DIY. In theory, you could do the ductwork and even run the lineset, but leave it for an EPA certified tech, with the right equipment, to make the connections and charge the system. But it's not easy to find an HVAC contractor who will want to do that--for example, what happens if there are warranty issues?

   DIY ERV is a lot less problematic. So maybe you do the ERV and they do the Mitsubishi system?

1. Expert Member
   BILL WICHERS | Aug 03, 2021 07:03pm | #3

   Commercial HVAC contractors should be OK evacuating and charging refrigerant lines. They bill time and materials, and they don't guarnantee anything outside of what they did, since they didn't sell you the unit or do the installation. I've never had a problem with something like that, and I do contract for this all the time commerically since I have a LOT of air conditioning equipment that I manage under contract at work. Leak testing, evacuation, and charging are easy for the contractors to bill as time and materials jobs. If a residential contractor doesn't want to do it, call up a commercial contractor. You should have no trouble finding someone willing to do the work.

   I do recommend encouraging them to start the project a little before lunch. Have them connect the lines and start their vacuum pump before they take lunch. This way the vacuum pumps runs over lunch, and you can often keep labor hours down this way. This also helps to encourage them to run the vacuum pump long enough to get a good vacuum in the lines prior to charging, which is better for the system.

2. Expert Member
   BILL WICHERS | Aug 03, 2021 06:48pm | #2

   Duct work can be tricky and requires some skill. The other "big issue" with trying this as a DIY project will be the refrigerant lines. You can easily run the lines yourself, but charging them is much more complex. You need to evacuate the system, then charge it, and these are critical steps for proper operation of the system. You might be able to get precharged units, but you still have to evacuate the lines.

   What you might try to do is a hybrid approach where you DIY what you can, and contract out the rest. Running the refrigerant lines and electrical lines are easy to do. You might be able to purchase some of the equipment yourself too, possibly saving a contractor's markup. I would consider contracting out the duct work, since that can be difficult to do if this is your first time, and you won't have the equipment to fabricate any custom transitions that you might need.

   I would absolutely contract out the refrigerant charge since it's critical to get right, and you can damage your system if you don't.

   I would absolutely run my own electrical lines, including for any wired thermostats you may have. This stuff is easy to DIY.

   Bill

3. 
   arnoldk | Aug 03, 2021 07:04pm | #4

   Hi,

   My initial thought was to leave the final steps of connecting everything including the referent lines to the unit and balancing the system for the pro's to do but I would do the ERV and the duct work.
   The electrical and low voltage I will be doing when I complete the wiring for the house since I worked in electrical trade for a short time.

   Thanks,
   Arnold

4. 
   arnoldk | Aug 04, 2021 02:54pm | #5

   Hi,

   I was advise by one HVAC contractor that the two cold air return could not be ducted because "There isn’t a way for us to run duct in this space. We need the 3.5” X 14” cavity X2 for each return on this design and going from floor joist spaces to stud spaces just isn’t feasible."

   How crucial is it have make sure the cold air returned are ducted and not simply using a floor or wall cavity?

   Thank you,
   Arnold

1. 
   DCContrarian | Aug 04, 2021 07:56pm | #8

   I'm guessing fire code. The same cavity with sheet metal ducting offers a measure of fire containment.

5. 
   mgensler | Aug 04, 2021 04:51pm | #6

   I would ask them why they can't do it. Seems like they cutout the bottom plate of the wall and subfloor to connect the sheet metal. Panning is easy and it sounds like they just want to take the easy way.

1. 
   arnoldk | Aug 04, 2021 05:08pm | #7

   Hi Mgensler,

   I suspect you are correct that they simply don't want to do it since most HVAC contractor use panning for air return.
   They haven't gotten back to me with more details as to why it cannot be done but I have reached out to them with the attached drawing showing a possible solution.

   Thanks,
   Arnold

   
1. Expert Member
   Akos | Aug 04, 2021 08:46pm | #9

   Arnold, what size are the floor joists for the 2nd floor? You can definitely do a fully ducted return with runs going up through walls. I've done this before in retrofit situation and even there it is not a big deal. Make sure your wall framing lines up with the floor joist framing bellow in any location where you want to bring up ducts.

   You can also do a jog in the bedroom wall and upsize the section of the wall from the corner until the end of the return and go with a single 8x14 return duct instead of trying figure out how to duct to two bays.

   You do have to watch your equivalent length as some of the fittings for these are extremely restrictive (ie reverse stack elbow).

   For a high performance home you don't want panned returns. There is no way to guarantee the panned return does not leak, you'll be sucking in outside air through leaks in your framing and dust and dirt into your return. A well sealed return with a filter grill means your equipment and ducts will stay pristine for years to come.

   Everything should be hard pipe with maybe short runs of flex at each room for a bit of extra sound isolation.

   P.S. I think it would be simpler to do a ceiling air return on the main floor instead of trying bring it down in the wall.

1. 
   arnoldk | Aug 05, 2021 07:56am | #10

   Thank Akos. The reason you mentioned is why I want everything duct including the return air.

   I'll mention your suggestion to put the air return on the ceiling instead at the bottom of the wall. Question, why are return air on the second floor often up high on the wall while the first floor and basement they are at floor level?

   Arnold

1. Expert Member
   Akos | Aug 05, 2021 09:05am | #11

   In most cases air leaks happen near floor or ceiling level. In the winter this means stack effect is drawing cold air in near the main floor and in the summer hot air near the ceiling upstairs. Without a return there, this air would get stuck and make the place uncomfortable.

   With a well sealed place, this is less of an issue but you still get stratification because of the height of the building, thus the need for a high 2nd floor return for good cooling performance.

   Also in most cases the air handler is in the basement, so having low returns in the basement and the main floor is simpler ducting.

6. 
   arnoldk | Aug 06, 2021 10:45am | #12

   Hi,

   The HVAC is recommending for a hybrid ERV system since I'm doing a full duct heating system. They suggest doing an exhaust only system in the bathrooms and kitchen but supplying the fresh air by utilising the heating/cooling ducts.

   Is this recommended or should I stick with my original design by having a fully dedicated duct system for the ERV?

   Thank you,
   Arnold

1. Expert Member
   Akos | Aug 07, 2021 09:05pm | #13

   I've done a number of these as it is a much simpler setup. It also has the benefit of pre-heating and pre-cooling fresh air. I would also put a stale air pickup in the primary bedroom as this will guarantee air changes no matter what speed the air handler runs at.

   Since you are running a modulating heat pump the blower on the unit will run 24/7, which generally means decent fresh air distribution, I would still check that at the lowest modulation point all rooms get enough air.

   The important detail with this type of setup is to have low pressure drop across the return duct, this should be generally bellow 0.1" with the air handler running full tilt. If you get an autoblance ERV, this is less critical as they can usually handle a fair bit of pressure change without effecting airflow.

   I would also add a damper to the fresh air intake wired to the ERV's blower interlock output so you don't pull outside air through the unit when the ERV is off and freeze the core.