Replacing old range hood w/ over range microwave

[jeromedawg]

Hey guys,

Was curious on the replacement of a range hood with over range microwave if I can use something like a 'flexible' dryer vent hose or maybe something else (not really sure what) in place of the rigid galvanized steel ducts that are currently in place - there's a small section that the previous installer (from 10+ years back before we moved in) had cut and appears to have attached to extend from the adjustable 90-degree galvanized steel elbow into the current range hood. This appears to be 8" diameter galvanized ducting  it's patched up with duct tape and is just super ugly and I'm positive there is leakage.

Anyway, for the new microwave I'll likely be getting these:
https://www.lowes.com/pd/IMPERIAL-10-in-x-3-25-in-x-7-in-Galvanized-Steel-Straight-Stack-Duct-Boot/1000228333
https://www.lowes.com/pd/IMPERIAL-8-in-Dia-x-7-in-Dia-Duct-Reducer/3664090

Wondering if the awkward section of galvanized steel can be replaced with something durable but more flexible. I'd prefer not to deal with having to get a new section of galvanized steel duct and have to make odd cuts in order to conform it to the new over range microwave setup. If there's something that can be cut easier and bend/flex that would be great. I figure this may be less desirable though because perhaps the ridges that make these types of flexible hoses/ducts *flexible* probably is more prone to catching grease, and lint right?

Here are some pictures of the current configuration:

[lthenderson]

My state code doesn't allow for flexible ducting because it restricts air flow, builds up debris, can be a fire hazard and is generally not as durable as rigid ducting. Definitely use rigid. Also, don't use that duct tape that was used previously. Buy the metal foil tape for ducting. Plumbing those up definitely isn't my favorite of jobs because it is tedious PITA work but if you just take your time and do a good job with the metal foil tape, they look a lot better in the long run.

[jeromedawg]

My state code doesn't allow for flexible ducting because it restricts air flow, builds up debris, can be a fire hazard and is generally not as durable as rigid ducting. Definitely use rigid. Also, don't use that duct tape that was used previously. Buy the metal foil tape for ducting. Plumbing those up definitely isn't my favorite of jobs because it is tedious PITA work but if you just take your time and do a good job with the metal foil tape, they look a lot better in the long run.

Thanks. I figured that might be the case after thinking it through. Guess I'll just use what's in place. I did buy some aluminum/foil tape as well as the boot and fitting I linked prior. Looks like I'll be having to do it the old-fashioned way and crimping with a pair of linesman pliers. I'm apprehensive to remove that duct tape and that space is super difficult to work in but I'll just have to deal with it all. When applying the foil tape, how long of pieces do you typically work with especially in these tighter spots? 

[lthenderson]

I usually get a piece that is slightly more than half the circumference of the pipe in length. I peel one end of the backing and carefully feed it between the pipe and the wall and get it centered where it is needed and then stick the end, pull the tape and stick the rest. Once I get the backside done, I then do the same with the front overlapping the back piece of tape on both sides. It creates the effect of looking like one piece of tape all the way around but much easier to do neatly.

[NorCal]

I just did the same thing, and surprisingly the old duct fit perfectly with the new microwave.

It looked like standardized sizing/dimensions, but maybe I just got lucky.

There’s a decent chance yours will line up too.

[jeromedawg]

BTW: I removed the hood and cleaned it up - glad I got that thing off. But the next challenge is getting the microwave up and filler blocks in the gap spacing between the microwave and the cabinet - there's a front overhang so it's not going to be flush. The vent had a series of shim blocks (1-3/4") air-nailed into the bottom of the cabinets so unless I want to crowbar those out (which I don't really want to do at this point), I'll need to add a couple shims in. I have some 2x4 pieces but still need an additional 1/4" shim - I happened to stumbled across an old piece of cedar that's 1/4" thick but was used to repel moths in the closet - the hanger piece broke off, leaving a nice rectangular piece that I can cut in half and use to shim the remaining 1/4" space. The 2x4 is a piece of pinewood. Is it OK to use the cedar wood to support and bolt the microwave from the top? I have to add two bolts in from the top cabinetry, which is where they suggest using the filler blocks/shims in case you have a gap due to a front overhang, etc.

EDIT: it looks like I will have to remove these shims - I don't quite know the best way to get them out considering how they were nailed in with an airgun from the bottom up :( I don't want to damage the existing cabinetry so this will be a challenge. I have some wood chisels and a small crowbar so I guess I'll have to just work at it unless someone can offer a better alternative. Unfortunately, I cannot reuse the shim as they are in their current positions because they don't line up with the bolt holes for the microwave. So it's best just to remove them completely and install new shims in the proper places where the bolts are going to go:

[jeromedawg]

I ended up just starting some cracks with the chisel and then was able to hammer the short crowbar in and got the shims off. Likely won't be reusing those, especially with all the nails/staples that are sticking out of them. I will probably just cut a couple 3" or 4" sized square filler blocks for the bolts to secure the microwave. Still wondering if I should or shouldn't shim the 1/4" space with that piece of cedar...


The other challenge is trying to make use of the installation template - because there's such a recess, it makes it really difficult to even tape the template evenly (compared to if it was just a flat surface). Pretty annoying but I think I may have to kind of do it the old-fashioned way and try to guesstimate where the bolt hole is by taking rough measurements

[lthenderson]

Rather than trying to tape a flimsy paper template in an awkward place, tape it to a stiff piece of cardboard on any comfortable surface, mark and drill your holes, and then hold the piece of cardboard up and mark and drill your holes through the wood.

[jeromedawg]

Rather than trying to tape a flimsy paper template in an awkward place, tape it to a stiff piece of cardboard on any comfortable surface, mark and drill your holes, and then hold the piece of cardboard up and mark and drill your holes through the wood.

That's a great idea. I ended up 'free-handing' it with the holes - hopefully they match up lol.

Someone else had suggested that I forego the filler blocks and instead beef up and add frame-support to the cabinet above the microwave. The bolt will pull the microwave up to the front overhang but there's nothing in the back - adding some support in the back would help bracket the cabinet/shelf to prevent it from falling down.



The yellow outlined item would be a 1x6 piece of hardwood board and the red dots would be the wood screws securing the board in place (two in the front/face of the frame and two going up through the back of the plywood shelving and into the solid wood back support strip). Not sure if additional brackets would be recommended after that but I'd do it on the other side as well. Then I can shim that space or certain parts of it as wanted or needed.

[lthenderson]

I wouldn't waste my time supporting the back of the cabinet. All the load of the microwave is split between the front two screws and the metal bracket screwed to the wall. Once you get the back of the microwaved clipped into the bracket, it requires very little force to hold it up while getting the bolts started.

[jeromedawg]

I wouldn't waste my time supporting the back of the cabinet. All the load of the microwave is split between the front two screws and the metal bracket screwed to the wall. Once you get the back of the microwaved clipped into the bracket, it requires very little force to hold it up while getting the bolts started.

Hmm, I ended up asking the question over at DIY Chatroom (https://www.diychatroom.com/f47/filler-block-cedar-shim-over-range-microwave-687353/) and the guys there are saying I should try to support it if I can especially because the shelves on the upper cabinet are only particle board (which I don't think I disclosed here). The microwave is significantly heavier (57lbs) than the range hood (prob no more than 10-15 lbs if that) that was previously in place

What was suggested at some point was this:
so I ended up cutting up a 2x4 I had laying around. And now I'm wondering if I should do this:


OR



Those are *not* going to come all the way down to hit the top of the microwave (there will be a bit of a gap but I could shim it if I need to meet the "filler block" suggestion). Otherwise, the thought behind these additional supports was really to just support the framing of the upper cabinet since it was was perceived that the framing is weak and could potentially collapse (particularly in the back)

It was also suggested that the vendor-recommended filler block (sandwiched between the microwave bolt hole and the bottom of the cabinet) is unnecessary.

Thoughts?

[jeromedawg]

nevermind...

[jeromedawg]

Okay, so I got it up but now am having trouble with the vent ducts:





This is the prior existing 7" duct work from the range hood. I have another section of 7" duct that I pulled out but it's big (the vent was lower profile so more room to work with the ducts). And I don't have any sheet metal shears to cut this stuff :(

Is there a way I can force it in to work or retrofit? If not, am I going to need to size down to smaller ducting? I'm not sure if there's a certain minimum requirement diameter for duct work in my area (Orange County, CA) if that's a factor.

Any ideas on how to get this to work out? I just read a blurb on the city's website about potentially needing a permit for hood and duct systems but there are no listed requirements or specifics about what's allowed or not allowed. Ughh... not sure if this was supposed to be 'permitted' work and if I'll have to end up removing it and hiring an appliance installer to do all this :T

[lthenderson]

Without tools, this is a tough one and very tight quarters. They do make offset boots where the transition to the round duct work is on one side of the boot instead of center like yours appears to be. If you can get one and move the transition to round duct farther away from the elbow shown, you might be able to get another elbow in there to make the connection. Personally, it would be easier just to get a hunk of galvanized sheet metal, duct flange and a handful of rivets and make my own transition but you would need a rivet gun and hand shears at the minimum.

As far as sizing goes, almost every installation manual I have seen for an appliance with ducting specifies minimum size ducting, distances, etc. I would look there first.

[jeromedawg]

Without tools, this is a tough one and very tight quarters. They do make offset boots where the transition to the round duct work is on one side of the boot instead of center like yours appears to be. If you can get one and move the transition to round duct farther away from the elbow shown, you might be able to get another elbow in there to make the connection. Personally, it would be easier just to get a hunk of galvanized sheet metal, duct flange and a handful of rivets and make my own transition but you would need a rivet gun and hand shears at the minimum.

As far as sizing goes, almost every installation manual I have seen for an appliance with ducting specifies minimum size ducting, distances, etc. I would look there first.

The installation manual recommends 6" minimum ducting. The ducting I have there now is 7" ducting which is what the original ducting was.