Cleaning a 130-year-old hydronic system before new boiler install - was it worth the 30+ hours?

RickT

So before I installed my HTP UFT-100W (I bought two new on ebay for $1k each, which I posted about previously, still working on the install), I decided I should probably clean out my ancient system.

I should first say: I'm not a pro, this is all diy and learn as you go. My boiler burned earlier this year so I'm on an adventure that will end up saving me thousands but obviously very time consuming and still has a lot of expense.

Second: obviously you don't want to do ANY of this with the boiler, expansion tank, or any sensitive equipment connected; this was just the bare bones piping and old cast iron radiators. And also my trusty B&G single speed pump that has been running for much longer than I've owned the house on the existing system anyway.

The house is from the 1890s and I'm pretty sure the cast iron radiators and most of the black pipe are originally a gravity system that was later retrofitted to a pump with expansion tank. The water that came out when I drained it looked... well, not terrible actually. Kind of rusty orange when ran through a white cloth, clear looking in a bucket, and no black sludge or anything. But I knew there had to be decades of crud in there and I didn't want to kill my new boiler or my new Taco VT2218 variable speed pump right out of the gate.

I went down a bit of a rabbit hole on this cleaning process and figured I'd share what I learned, both the good and the spectacularly messy parts.

The Setup

My system is about 150 gallons total with nine cast iron radiators across two floors (the house also has a second steam system that hasn't functioned in decades; I'm in the process of sourcing salvage hot water radiators and adding these parts of the house to the hot water system).

The piping is a mix of original black pipe and about 20 feet of newer 1 inch PEX sections where I made repairs after a very long term galvanic corrosion leak at the supply of one radiator (it had been leaking a long time and finally failed; all other connections still look great btw).

For the cleaning I set up a temporary loop in my basement, using about 25 ft of non oxygen barrier 1 inch PEX A (non O2 barrier for a temporary cleaning = fine) and a point-of-use electric water heater (14 kW) to heat the cleaning solutions, with a garden hose connection on the inlet side and drain valve on the return side. This let me fill, heat, circulate, and drain without having the new boiler connected yet. After flushing the hot water heater I plan to resell it. I already had a bunch of 6 gage wire lying around so was able to use that and a 50A breaker (but I had to be careful to manage the power consumption of the heater using the temperature controls because it would trip the breaker after a few minutes at full power; supposed to. be on a 70A breaker).

Round 1: TSP

I started with trisodium phosphate because I'd read it's good for loosening crud without being too aggressive on the metal. Mixed up about 3 pounds in the system and heated it to around 140F, let it circulate for 26 hours. When I drained it the water came out pretty dark, definitely darker than what came out initially.

But here's where I learned something important. After draining I tried reverse flushing by running city water backwards through the system (in the drain side, out the inlet side). Holy crap, the water that came out was BLACK. Just pitch black for probably 20 minutes of flushing before it finally started running lighter. The TSP had loosened a ton of crud but it was just sitting in the radiators and low spots, not actually leaving the system until I forced it out.

Round 2: Citric Acid

After the TSP I moved on to citric acid, which I'd read is better for actually dissolving bonded scale and rust. I used 3 pounds of food-grade citric acid powder in the 150 gallons, heated it to about 140F (max temp for the water heater) and let it run. I was planning on 24 hours but I stopped after about 18 because the water in my drip bucket (there was a small leak at a temporary fitting) was absolutely jet black. I figured the acid must be spent at that point. It was so black (similar to the TSP water) that at this point I became suspicious that a lot of that black water was probably still leftover from the TSP cycle that had been hiding in even more dead spots, not necessarily all new stuff the citric was pulling out.

Drained it and did another reverse flush, and again, BLACK water just kept coming and coming. I flushed back and forth for probably 45 minutes through both sides (supply and return which I didn't do multiple of before) until it finally started running just yellow instead of black. Never got fully clear this time.

The Compressed Air Discovery

This is where things got interesting. I have an air compressor and I'd bought a quick-connect adapter to connect it to my system (3/4" female garden hose thread to 1/4" male quick connect for air tools, for anyone keeping track, about $7 at Menards). I was going to use compressed air to help target specific radiators during a second citric cycle, because those rads had never gotten hot from the 140 degree water (this is a lot cooler water than the system had ever had in it before, obviously, so I think that's why...) but I decided to do a test run first.

When I pressurized the system to 40 PSI with just the little bit of water that's impossible to fully drain out, then opened the drain valve to blow it out, BLACK water came spraying out. Really nasty stuff. I thought I should probably do it again before more acid treatment, so filled the system partway with fresh water, pressurized it with air, and blew it out hard. Even more black water. I kept doing this over and over, filling partially while pressurizing to 40 PSI (this slows filling but you can force the water to specific radiators by open their bleed valves- all my radiator valves are completely seized btw) then blowing it all out forcefully through the drain.

This compressed air blow-out method turned out to be incredibly effective. The pressurized air and water together creates this scouring jet action that physically dislodges sediment that gravity draining just can't touch. After probably 3 hours and half a dozen cycles of fill-pressurize-blow, the water was finally coming out pretty clean.

Round 3: Second Citric Cycle (and Disaster)

Since I'd already mixed up another bucket of citric solution before testing the compressed air setup and discovering the hiding black stuff, I figured I'd run one more cycle. I loaded it into the system and got it circulating. Remember that temporary connection that had been seeping a little bit since the beginning? The black steel bushing threaded into a black steel coupling on the cold side of the water heater? Well, after about 6 hours of citric acid circulation, I came downstairs to find my bucket overflowing and acid spraying everywhere. Probably 20+ gallons of citric acid solution all over the basement floor.

When I took apart that connection after draining everything, I found that the acid had actually eaten channels into the threads on both the bushing and the coupling. It looks like the citric concentrated at that leak point and just corroded the stink out of those thin threads. The other connections that weren't leaking were completely fine. Lesson learned: fix ALL leaks before running acid through your system.

Final Cleanup

After the acid spill I did another series of compressed air blow-outs with fresh water. Still got pretty dirty water initially, though noticeably cleaner than the first round of blow-outs. I eventually disconnected the water heater setup, established a simple loop with PEX fittings, and circulated fresh water for about 36 hours while waiting for my corrosion inhibitor to arrive.

PART II NEXT POST

RickT

The Inhibitor

I ended up going with ChemWorld Boiler Rust Inhibitor from Amazon. It was $57 for a half gallon that treats up to 250 gallons, way cheaper than the Fernox F1 or other retail options I was finding at $150+. I know some folks will say to stick with the name brands, but at that price difference I figured it was worth trying. The product specifically says it works for closed loop systems and has good reviews, so we'll see how it holds up.

So Was It Worth It?

This whole process took maybe 30 hours of actual hands-on work spread over about a week (a lot of that time the system was just soaking while I worked on other parts of the install or, you know, slept). I spent roughly $300 on chemicals, fittings, and supplies.

Here's my thinking on whether it was worth it. If I were just protecting the boiler, I'm honestly not sure. The water that came out initially didn't look that bad. I don't know what pros would have done; maybe just a quick powered flush or maybe a single TSP cycle and called it good? The boiler probably would have been fine, maybe lost a bit of efficiency over the years.

But I'm also protecting a $500 Taco VT2218 variable speed pump, and from what I've learned, those high-tech pumps with their tight tolerances and electronic controls do NOT like dirty systems. Sediment can damage the sensors, clog the precision impeller, and cause premature failure. For a sophisticated variable speed pump, a clean system isn't optional, it's essential.

Plus I learned a TON about my old system during this process and how important it is to have places in the new piping panel I am building now for connections and future maintenance. I know exactly which radiators get good flow and which don't, where the air pockets like to form, and I developed this compressed air blow-out technique that I'm pretty sure is way more effective than just draining and refilling. I'm also mulling over how to modify the piping to fix my uneven flow issues (I didn't talk much about that but with my seized valves it's a real challenge).

The system is absolutely much cleaner now. When I was doing those final blow-outs the water was coming out crystal clear. My new boiler and pump are going into the cleanest 130-year-old hydronic system in Ohio.

Lessons Learned

Reverse flushing is critical. Just draining after a cleaning cycle leaves tons of crud sitting in the radiators and low spots.Compressed air blow-outs are incredibly effective. Fill partway, pressurize to 40 PSI, blow it out hard. The combination of air and water scours out sediment that gravity can't touch. I think this should be standard practice for cleaning old systems. Don't do this with the expansion tank or boiler or other sensitive system components in the mix, though! And fix all leaks before using acid cleaners. Citric acid will attack any connection that's leaking, and it's aggressive about it.Multiple shorter cycles with aggressive flushing between them probably works better than one long cycle. The crud needs to be physically removed, not just dissolved.Variable speed pumps really do need clean systems. If I'd been installing an old-school mechanical pump I might have skipped some of this, but protecting that VT2218 made it worth the effort.

Would I do it again? Yeah, probably. Though next time I'd skip the second citric cycle and just do TSP, thorough flushing, lots of compressed air blow-outs, and then inhibitor. That would have saved some time and avoided the acid spill disaster.

Anyway, figured I'd share in case anyone else is facing a similar decision about whether to clean an old system before a new install. Happy to answer questions if anyone has them.

hot_rod

You certainly went the distance on the clean. Probably the most critical component to have now is a magnetic separator. You did not, will not ever, get all that black magnetite out. So any of it that loosens will make it's way to any magnet in the system.

We call that black water "boiler ink" it looks harmless, let it settle in a glass overnight, stick a magnet in the glass. This identifies it as ferrous metal particles.

ECM circulators have a permanent magnet rotor in side them. So that black gunk WILL make it's way into you electronic pump. Regardless of what pump manufacturers tell you :)

Here is an exploded view of that rotor, pulled out of the rotor can that it spins in.

That part is filled with the system water, so magnetite at a .05 micron size makes it way into.

Part 2 is to maintain the mag sep. Flush it weekly util you get hardly any particles out.

It's good to know a little about the water you fill with, hardness, TDS, chloride levels.

Your boiler manual should have a water spec like this.

RickT

Love it! I'll definitely spring for the magnetic filter, sound like money well spent. Maybe I'll go get one from the pluming supply store and run it in the existing cleaning loop for several days before I disassemble it in preparation from the final connection to the new system.

(haha listen to me "several days"- at this rate it will likely be weeks before I finally get the new into service… gawd)

RickT

Question: I'm using a Spirovent air eliminator. If I put a MagnaClean in place, given my old system would I benefit greatly from also adding a dirt separator, like the Spirotrap…? All of these things certainly add up. I feel like I already evacuated most of the sediment etc. out of it though with the thorough cleaning- maybe I can skip the dirt trap.

SuperTech

I enjoyed reading this thread. I think the effort you made to clean your system will be worth it.

Unfortunately I think you will be disappointed once you start using that $500 delta T circulator. It's really doesn't work the way you think it should. No matter what mode you operate it in its never "variable speed" or modulating. It just cycles 100% on to 100% off. It doesn't vary the flow based on the delta T.

hot_rod

Rust never sleeps , my friend! If O2 is getting in, and it is, corrosion will continue

If your boiler treatment has an oxygen scavenger ingredient, that will help. But it needs to be boosted from time to time.

Either a combination device, or two separates

Air removal is usually supply out if the boiler

Mag and dirt on the return side.

Can’t go wrong with Caleffi products. We pioneered the various separation devices, especially hydraulic and magnetic

RickT

https://forum.heatinghelp.com/discussion/comment/1871164#Comment_1871164

Really?! Huh. All advertisements say it's an ECM pump!

Is there a pump should I consider instead, in your opinion?

mattmia2

You want a magnetic dirt separator if you are putting a wet rotor circulator on a converted gravity system or really any system with steel piping or ci or steel emitters.

A pool pump would be a better choice for your pump cart to flush the system, a 3 piece circulator is designed for relatively low flow and head, a pool pump or even big sump pump would created more flow where it has to lift the water and flush more of the sediment out. A shop vac is good for creating more velocity to move things along too.

TSP won't do a lot to make minerals dissolve, it will just loosen particles up and allow them to move with enough flow. Citric acid will make the mineral salts and the iron itself soluble in water.

Most installers would just put some system cleaner in the old system and let it circulate for a few days and flush it out then let the magnetic separator do its job.

RickT

Did a little more research: it seems what you're saying is essentially correct. It still ramps up and down but it does it fast, "hunting" for the right temperature by ping ponging between a fast and slow speed essentially and it never settles on a single speed to manage a constant delta T, which is DEFINITELY what I was imagining.

Maybe I'll return it and just get a Grundos constant pressure pump.

hot_rod

The circ you have is an ECM. That refers to the type of motor. PSC permanent split capacitor is what a pre- ecm circ used for a motor.

In some cases that circ you have may work better in a fixed speed mode. It still uses less energy, but the variable speed function is not working.

A system that is zoned with zone valves, radiator valves, TRV works better with a delta P, pressure differential type control logic. The pump "sees" a change in delta P as valves open and close and varies it's speed accordingly.

I don't think your pump has a ∆P option.

SuperTech

https://forum.heatinghelp.com/discussion/comment/1871177#Comment_1871177

I think there's quite a bit of false advertisement with that circulator.

I think the Alpha circs are more useful, especially with zoning.

RickT

Thanks guys.

No: the Taco VT2218 doesn't have Delta P, just Delta T. Also has fixed speed modes.

What I like about the idea of the Delta T pump is not having to worry about gaining a deep understanding of how pressure translates into GPM flow rates, and how that translates into Delta T. It's just a lot of things to understand and keep track of and I like the idea of just "knowing" that the pump will get me the targeted Delta T (regardless of HOW it does it: "hunting" or not, I don't care) and I can focus on comfort levels in different parts of my system…:

• Zone 1 is going to be the existing large diameter black pipe and oversized cast iron rads
• Zone 2 is going to be modern 1/2" PEX with salvaged rads (probably will end up oversized but hopefully not if I can find smaller radiators…. these are smaller rooms) and 1 more properly sized baseboard in my kitchen
• Zone 3 is going to also be modern 1/2" PEX, with two properly sized baseboards and two salvaged cast iron rads (these will almost certainly be a little bit oversized)

I have 3 Taco Sentry zone valves. I'm doing direct piping (no primary-secondary) with a bypass to maintain the boiler minimum flow rate so I can get deep condensing (maybe 110 degrees average temp?) in mild seasons (when enough zones are calling for heat and the bypass isn't open).

BTW I'm getting the salvaged rads partly to save money but partly for the aesthetics of the house.

So my thinking is with a very complicated mixture of emitters like this, and a complicated mixture of losses, the Delta T functionality- even if it doesn't work exactly as advertised- will help me a lot because at least the pump is automatically getting the temperature differential handled across the whole house, and I can focus on turning ball valves on zones and on individual radiator circuits to bring things into balance over time (I anticipate it will be a longer process to get there- partly because of the complications, but also because there's no way I'm going to get all these new emitters installed in this current season).

I'm an engineer (civil, not mechanical) and I am very given to making this complicated and wanting to always calculate every single thing. Without the Delta T management I anticipate that every time I go to adjust a valve, I'll be getting out my spreadsheet and calculating the Delta T and all these things and I just don't have time for it…

RickT

https://forum.heatinghelp.com/discussion/comment/1871179#Comment_1871179

Yeah I noticed that the pump barely did ANYTHING- the compressed air was when I really started to get things to move! Although running city water back and forth did seem to help some too.

Part of the issue was cost sensitivity for the cleaning part: TSP and citric acid are CHEAP compared to the usual cleaners (F3 etc). My system is 150 gallons and it was going to be well over $100 of just cleaner! A few bags of TSP and tubs of food grade citric acid did the trick for a lot less.

It's good to know that what I've done will only HELP compared to what pros would do (even though maybe it was more time and effort than I needed to put in, haha)- and I ordered a magnetic filter yesterday! Thanks for all the input, fellas!!

hot_rod

That ∆T mode of operation is often referred to as constrained ∆T. The pump attempts to maintain a fixed delta. Is that a good or desirable operation method?

Would you drive a vehicle that was constrained to a fixed rpm range, up, down hill, under heavy load, regardless of changing highway conditions?

The load on a building constantly changes based on temperature, wind, occupant use, internal gains, etc. So ideally a heating system that could monitor that and change accordingly would be good. Allowing the delta T to move around as loads inevitably change a common way to control.

The delta T is an indication of how much heat is being transferred at any given point in time.

Cold start up expect to see a wide delta. As the room warms, load drops, the delta will drop, maybe to a few degrees. If not constrained.

Heat transfer is related to temperature differences. Output charts for most any heat emitter show that relationship. More reading in the attached link Idronics 23

Higher flow rates= tighter delta = higher average temperature across the emitter = higher output. That is stated in the Laws of Thermodynamics.

If you use outdoor reset control, and you should :) then ∆T control logic will fight the ODR function.

Your high mass radiators will compound the effect of constrained operation.

https://www.caleffi.com/en-us/magazine/23-heat-transfer-hydronic-systems

RickT

Thanks.

What I'm getting from this is you really have to carefully design your ODR curve, directly taking into account whichever pump you select. It will not be the same for a Delta P pump and a Delta T pump.

hot_rod

A perfect or near perfect ODR setting takes some time and practice. It's not a number you can pull out of a book. Every home and homeowners expectations are different. If you get a good quality ODR control, you have endless adjustment opportunties.

In some cases an indoor feed back helps fine tune even more.

Just because outdoor temperature is dropping doesn't necessarily mean supply temperature needs to increase.

Internal gains from people, cooking, laundry, showers, etc all add heat to the space. The tekmar system allows both indoor and outdoor inputs for fine tuning.

Tekmar has excellent essays explaining how the technologies work together. Search around some a legacy documents

https://www.watts.com/our-story/brands/tekmar/references/how-outdoor-temperature-reset-controls-save-energy

RickT

Thanks!

Did some more research this morning: here's what I'm thinking.

Right now I think the Delta T pump actually makes the most sense, because given the details of my system, it cannot maintain 20 to 25° Delta T... And this is a feature, not a bug. On cold days, the system curve limits the flow to something like 6 GPM, so my actual Delta T ends up being more like 30 to 35° on those days… And the pump system stability feature ensures it never exceeds about 65% Max RPM; It detects that the Delta T has stopped changing and then just holds without trying to push more (because my cast iron emitters, both existing and the salvage ones I'm getting, are way oversized).

And for mild days. I just utilize the minimum setting on the pump, setting it to about 30%. The pump can't go any lower than about 2 to 3 GPM, so in shoulder season the Delta T ends up being more like 10 to 15°. Which is great for the baseboard emitters because it limits stratification.

An important detail though is that I need to oversize the baseboards. Happily, I'm not putting that much baseboard in, just less than a handful of rooms.

Could be wrong about all of this! But the math seems right to me.

RickT

One other detail is all the baseboard rooms save one are connected through open doors to rooms with cast iron 100% of the time. I am a little concerned about the kitchen, which is going to be on baseboard because of space issues and because It is not as connected to the rest of the house to get heat from the cast irons, but I'm not so much worried about that because it has a mini split that can supplement the heat if it really starts to get to be a problem. I don't think it will get that bad though.

hot_rod

https://forum.heatinghelp.com/discussion/comment/1871411#Comment_1871411

So you bought an $$ circ to specifically maintain your selected ∆. But it doesn't for the reason explained above with ODR upsetting it. But you are comfortable with that result, so go for it.

With the mix of high mass and very low mass emitters mixed, you want as few on/ off cycles as possible due to the thermal lag of the high mass. So to me a fine tuned ODR has more value that constrained ∆. Which you don't have anyways.

What does math have to do with it at this point? 😚

Constrained ∆ operation:

Stratification has more to do with higher fin operating temperature than ∆. Hotter convection currents will rise higher, quicker.

Run the entire system at the lowest possible SWT for comfort, efficiency, less component cycling. That is the job of ODR, not constrained ∆ operation.

Your issue may be the difference in how fin tube transfers heat opposed to radiators. Finned tube needs enough temperature to get the convection going and mix the room temperature.

Radiators are largely radiant transfer, that's what people love about them. Some convection depending on the type of radiator. I've run cast radiators as low as 120 SWT and they still feel great against my 90- 98° skin temperature.

Not much heat to you or the objects in the room standing in front of a fin tube. Meager output with 120 SWT at 30 ∆

The radiator heats by long wave radiation striking anything it can "see" in the room.

At days end, it what makes you smile, and comfortable, regardless of how you get there.

RickT

Thanks!

Had a little bit of evolution in my details since last time: I did not realize until this weekend, after doing some more calculations, how MASSIVELY oversized my existing cast irons are. They are HUGE. I can run them at 135 supply temp on design day continuously and still be just fine!

I'm now planning on running two design temperatures so I don't have to oversize baseboards, and can run hotter water in them without short cycles in the cast iron. Going to do this with a cold water buffer tank (I actually have a 40 gallon gas water heater that I am not using for anything in my basement right now, perfect for a tank).

So I will set the cast iron at about 135 supply temp with a mixing valve, using the cast iron return water as the cold buffer via the tank (115 return water on design day). I'll program the ODR based on about 185 on design day for the baseboards. I'll get a delta T of about 30 on design day, so my return combined water temp on design day should be getting close to condensing if not condensing (although that's not really my goal, just a nice side benefit). I'll get very good condensing on moderate days.

However I'm worried about bb stratification even at 10 degrees delta T because the GPM in my emitters is going to be so low, so I am thinking about adding a small secondary pump to boost the GPM just in the bbs. The salvaged radiators won't be part of that additional pump trunk.

I still like the constrained delta T… it gives me more confidence that I am doing the programming for the ODR curve correctly… if I had to do it with constrained pressure instead, the math just doesn't make sense to me. I tried making a spreadsheet using constrained P and it just didn't seem to all come together. My brain couldn't understand it. But if I can know I'm getting a delta T of about 30 on cold days, 20 on moderate days, and 10 on mild days, it makes the math so much easier…

hot_rod

If you search around HH you will find contractors first hand experiences with ∆T and ODR. A demo is this simple.

Two way ro regulate heat output, temperature and flow. Temperature regulation is very linear, which is why ODR can be so useful. Reset graphs tell the story.

Modulating flow is nowhere near as linear.

I'm still not following what you mean by BB stratification?

Good news on the over-sized rads being useable with 135° SWT.

RickT

I just mean using only 1 pump I only have about 6 GPM available because of my system curve, so each bb would see a pretty tiny GPM: something like 0.3 to 0.5, depending on the bb. So the bbs would have to be pretty heavily de-rated for their output at such low GPM, and they have to get pretty huge as a result. Just not cost effective.

I thought about doing a secondary pump for the bbs only, which would work and keep the bbs much more reasonably sized, but that would result in a much lower delta T and ruin the ~80% of the season condensing that I wanted to see (when the hotter return water mixes with the low temp cast iron return water at the boiler).

Because of this challenge I've spent the last couple days exploring other options. I am now pricing imported panel radiators off of Alibaba. :) They are certified to be used in the EU/UK (EN 442) and they will provide NPT adapters for them too. Haven't gotten pricing back yet but from what I understand, panel radiators are used all over the UK and are intended to work great for condensing systems at low flow rates, so they could be just what the dr ordered if the cost is reasonable (it should be, but I don't know yet). My hope is I can reasonably obtain 3X oversized panel rads that will allow me to run 135 degrees throughout more of the house! But some rooms will still require 180, so I think I'll still be using the cold water buffer idea.

The panel in one of my rooms with a design load of about 4100 has to be about 6 ft tall x 3.5 ft wide!!! Sheesh. But they look pretty nice/stylish, actually, and they aren't a piece of furniture taking up a huge amount of floor space like cast irons (stick out from the wall 4 inches max), so it won't be too bad.

Thanks for the additional info! I'll definitely be digesting it. I will point out though that- it seems to me, anyway- the final chart suffers from the flaw that in reality, delta T pumps don't actually constrain the delta T to 20 degrees, like in that example. The delta T naturally changes throughout the season because it is constrained by the pump flow capacity in the cold season (results in higher delta T), and by the pump minimum flow setting in the mild season (results in a lower delta T).

I wonder what that orange curve/line would look like if it were modeled based on a real-world constrained delta T example. Might line up much better with the red line. But I dunno man I'm not a mechanical engineer or HVAC person, I'm just a dude.

hot_rod

why would you spend $$ on a delta T circ that isn’t actually doing that function. With a standard or delta p you get this same result, variable delta.

Bottom line the pump attempts to match the load with flow adjustments.

Matching the changing heat load by varying temperature is an accurate proven technology, very predictable, called ODR outdoor reset. So common that most boilers have some version included. Why make it more complicated?

RickT

I don't think it's more complicated, just different. And it was easier for my brain to initially understand.

However, with the help of your consistent input, I took a LOT of time to deeply investigate this issue and I believe… I think (I am still hedging a little, but just a little!)… I have decided to return the Taco pump and get a Grundfos instead. I will explain my reasoning thoroughly in a later post (with charts! and numbers!) but the short version is the following:

https://www.youtube.com/watch?v=edyVNlo5uW0