Layout for ductwork and register questions

[machsnell]

I have a 1600 sf garage and i am installing my own ductwork and heat pump to be hooked up by a professional. I will do the time consuming work and have a few questions.

I am in Northern Virginia.

1. i have 3 doors. they are 2" insulated metal doors.

2. I have a 61k btu pellet stove that will run on its own thermostat.

3. i will have 6" of sprayfoam walls and 8" spray foam ceiling. open cell

4. I put insulation under my slab. 3" and the sides.

5. i have man door so garage door doesnt open ALL of the time.

6. It is fairly well shaded overhead and i have 6 dbl. pane windows that are 4 x 2

7. I will have 3 60" ceiling fans in there and ceiling height is 9 feet for most and a 26 x 16 that is 12 foot.

8. i know nothing about hvac. the bad.



Questions:

1. how important is it to have the registers at ground level. It is much easier to duct through the ceiling but want to know how much more important it is?

2. How important is it to have the air handler in conditioned space? ductwork wont and cant be without chase inside which i dont want to do.

3. a guy that originally quoted 10k for the ductwork and heat pump suggested a 3 ton with propane backup. Is that sound reasonable. I will not do the propane backup because of the pellet stove. just heat pump with strips.

4. Any suggestions for a total rookie with some skills in other areas?

5. I was planning on doing one trunk line and have flex take off that to ceiling registers OR to 3x10 square lines to registers if i take down to the ground level.


Thanks in advance for any advice.

 

[Charles (in GA)]

With those specs, in a VA climate, you are going to need little to no HVAC. The building will just about take care of itself.

I'd put it all in the attic, with thru the ceiling vents, or simply install a couple of good, large, minisplits and forget the venting altogether. As I see it (and I'm no expert) the pellet stove alone with probably provide plenty of heat, certainly no need for propane backup, and probably no need for the heat strips.

 

[Angry welder]

They only thing I would suggest is running your duct work in the ceiling and don't use flex line, instead use hard pipe and wrap everything. Using hard line makes it easier to clean everything out with brushes later on, granted you may never do that, also the wrap insulation can give you a better R-rating which will come in handy in the winter months. Also make sure you put dampers on your main trunk line to branch line connections. They will help even out the supply air throughout the garage. The return line does not need it.

 

[machsnell]

charles - thanks that makes me feel better and i hope and think you are correct but unsure.

Angry welder - going through the ceiling will make life much easier for a total novice. i have read on the install of dampers and will definitely do so to even the air. I am going to try and get a helper from one of my construction sites to help with the hard line. Unfortunately the flex is so easy but if i have someone to help with the metal i will do so. I was definitely going to run the trunk and return line in metal. thanks for your advice.

 

[davidlee]

You may want to get a second quote. I had a 3.5 ton heat pump installed a few months ago and paid $3200.00. I has 10kw back up heat strips. To be fair I did not need a whole lot of duct work because of my layout but unless running duct is really expensive that sounds kinda high.

 

[machsnell]

That is a great idea. I have a lot to do in the garage and not having to do that portion would be really nice. that sounds like a great deal. i need air handler also.

Considering the fact that i feel more comfortable ducting through the ceiling now it should cut the cost down also.

Thanks for ideas.

 

[Ohmthis]

May I ask why you are putting a ceiling in, or are you talking about the bottom cord is 9' off of the ground. With everything being foamed the whole place is essentially conditioned space. There for no reason, besides the duct temp not affecting the air as much to insulate the duct work. Defiantly run your duct over head and use round metal branches. Being sealed as good as it is you won't need 3 tons. Do (look online for it) or have someone do a Manual j. This will tell you how much heat and air you will actually need. Guessing on the size can have a real big effect on how comfortable your place is and how much you spend (both on equipment as well as utility bills). Good luck and ask if you have anymore questions. There are several here more than willing to help.

 

[machsnell]

yes my truss bottom chord is 9 feet from finish floor. The attic area is not conditioned. I didnt want to put in the spacers for air flow from soffit to ridge and then spray on that. also the cost would be greater for spraying that area.

There are 3 garage doors which the previous guy said would be the biggest source of leaking and incoming air.

The best place for the air handler is in the attic space as well as the duct work. I could find a spot for the air handler only but it sounds like the unless the ductwork is in conditioned space it doesnt matter about the ah.

who can do the calculation? a heat and air supplier?

Thanks

 

[7echo]

Any decent HVAC outfit can run a Manual J. But, there is a calculator on-line that I think cost $50 for a month of use. You can input all the variables and see what you need. You can go back and tweak a little here and there and see how much the load changes.

Like Charles suggested, check out the mini split options. Depending on the layout you may be fine with a couple of those. No duct work involved.

 

[7echo]

When I did my home renovation I used this calculator-

http://hvac-calc.com/main.asp

 

[machsnell]

Alright i had thought about the mini splits but i had enough space in attic and trusses to run the duct so and the ocd in me didnt want to see the wall units and i didnt have tons of wall space with cabinets and such.

However, ....i just looked at the minis and saw you can get the cassettes that mount in the ceiling. i also figured a way i could get the 3 wall units in if i had to.

So now i am leaning towards doing the mini splits.

Anyone know of a brand and a place to calculate what i need?

I will check with a local supplier and see if they can calculate if that is something they do.

Thanks for changing my mind. sounds much easier.

 

[Ohmthis]

Any HVAC outfit worth its own salt can do a manual J. You can also use the online versions, but I'm not really sure how accurate they are. Mini splits are a good option, but the filters need to be cleaned often, they aren't designed for a dirty environment.

 

[7echo]

Any HVAC outfit worth its own salt can do a manual J. You can also use the online versions, but I'm not really sure how accurate they are. Mini splits are a good option, but the filters need to be cleaned often, they aren't designed for a dirty environment.

Absolutely on the filter issue. They will need attention more often for sure. On the Mitsubishi ones we have at work they are all washable so that helps.

Another advantage, or really another way to view the options, is that there will be more storage space in the attic without the duct work.

 

[Angry welder]

To address some of the questions and statements I have glanced at. A/C unit size is determined by heat generated in the building. So if you have a lot of people in the building with a lot of body heat you need a bigger unit. If you are in a shop and the equipment is making a lot of heat then you need a bigger unit. Second the unit is also sized to the size of the building and the insulation value of the building. If you have an open ceiling and can see the roof trusses then there is no insulating barrier from the heat on the surface of the roof, and trust me roofs get hot quickly. Thirdly to save money and time, I would pour a concrete pad next to the shop and set a package unit beside it and run the duct work up the side of the building and into the roof line that way. If you don't want to see the duct work on the outside then build what they call a dog house around it. Running a package unit on the outside does have some benefits with what they call make up air. Its a vent on the side of the unit that opens to the outside air and instead of the unit compressor coming on just the fan motor will come on and will cool the building that way. It does help to save a lot of money running a 110 fan verses a 220 compressor when ever possible.