Water heater insulation

[Runs with bison]

I'll stand by my signature....

It is unfortunate that you have not done that in this thread.

[Dana]

One must also divide by the burner efficiency (for the mode the tank will be in when it fires just to bump the temp back up to set point...and that will be very low, something less than the 76% or so that it gets in cold tank recovery mode.)

Power vented versions tend to hit raw combustion efficiencies pf ~80-82% in cold water recovery mode, ~79-80% in maintenance (or in space-heating combi) mode these days. I'm sure it's somewhat lower than that for atmospheric drafted versions, but I'd still be surprised if it's ever under 75% in raw combustion efficiency, even with the cold end the water side of the flue heat exchanger over 120F. It's not a counterflow HX- the hottest combustion gases are many hundreds of degrees, and in contact with the coldest end of the HX, so the percentage difference in delta-T gas side/water side isn't huge between a ~60F (water side at the bottom of the HX) start and a 130F finish of a burn.

Still, I'm educable- got online references? (Or have you actually measured net stack & O2 under various modes?)

On the general fire-hazard theme, manufacturer legalese notwithstanding, can anybody point to a reference the number of house fires caused by water heater blankets per year/decade in N. America (or just team USA?) I can understand the impulse of manufacturers to limit their liablity in situations where it's theoretically possible to really screw it up (like DIY blanket stuffed into the flue or restricting combustion/dilution air, etc.), but how often are such installations ACTUALLY screwed up to the point where they cause a problem? (I'm thinkin' it's pretty rare...)

[Runs with bison]

Power vented versions tend to hit raw combustion efficiencies pf ~80-82% in cold water recovery mode, ~79-80% in maintenance (or in space-heating combi) mode these days. I'm sure it's somewhat lower than that for atmospheric drafted versions, but I'd still be surprised if it's ever under 75% in raw combustion efficiency, even with the cold end the water side of the flue heat exchanger over 120F. It's not a counterflow HX- the hottest combustion gases are many hundreds of degrees, and in contact with the coldest end of the HX, so the percentage difference in delta-T gas side/water side isn't huge between a ~60F (water side at the bottom of the HX) start and a 130F finish of a burn.

Still, I'm educable- got online references? (Or have you actually measured net stack & O2 under various modes?)

I pulled the 76% from the Energy Star reported value for recovery mode for typical atmospheric drafted versions like mine. I have not measured directly. I have directly observed the condensing characteristic in the early phases of cold recovery mode--with water dripping down the flue onto the burner and sweating from the combustion chamber roof. The gas side heat transfer coefficient is usually controlling for sensible heat with lots of inert non-condensibles, so when there is a condensing film the coefficient will be at its greatest. (The twisted flue/baffle helps of course, with or without the condensate.)

With a cold tank the top of the tank is going to be about 40-60 F colder than normal maintenance mode. While in normal mode the water at the top has not cooled substantially, it will be cold in recovery mode. So whatever the approach at the outlet was before it should be similar (if not less due to partial condensation). Take whatever the exhaust discharge temp was before and subtract the colder starting value from it initially. For the govt. reported value it is probably the average from start to finish.

As to how hot it is at the discharge and the excess air, I don't presently have the instruments to do that. I said in an early thread that measuring the temperature just before the exhaust exits the flue could be a neat trick for plumbers to evaluate when a unit was scaled/sedimented to the point it should be replaced. There is likely to be a death spiral where the outlet gas temp. increases and overall efficiency tumbles. Can't say for sure though without measuring dozens at different points in their life up to failure. If I was in the business it is something I would probably track.

I'm not really looking at power vented versions for the insulation blanket, though. I'm sticking with what I have experience with and can lay hands on: atmos. vent. In fact I was looking at a big box (because it was along the way) just to verify that the current line still showed the efficiency gain going from 1" to 2" insulation, all else being equal. They did and the 2" diameter increase was there as well. I also didn't see any automatic flue dampers on the atmos. vent models with the differing insulation...not sure how one would do that with a constantly lit pilot, but Doherty claims they do.

On the general fire-hazard theme, manufacturer legalese notwithstanding, can anybody point to a reference the number of house fires caused by water heater blankets per year/decade in N. America (or just team USA?) I can understand the impulse of manufacturers to limit their liablity in situations where it's theoretically possible to really screw it up (like DIY blanket stuffed into the flue or restricting combustion/dilution air, etc.), but how often are such installations ACTUALLY screwed up to the point where they cause a problem? (I'm thinkin' it's pretty rare...)

Exactly. I asked myself the same question. It's simply an attempt to avoid any potential liability for something that they have no control over.

[Redwood]

I'm not disputing the flue losses.

UA's work out to:
wall = 21/8 = 2.6
top head = 2/8 = 0.25
bottom head/flue = 5/1

Sum = 7.85

No surprise, the flue losses are dominant.

Thank You for confirming what I already stated...
What was it you were arguing about?


I'd go for the 95% efficiency myself....
http://www.bradfordwhite.com/images/...eets/123-B.pdf

[Runs with bison]

Thank You for confirming what I already stated...
What was it you were arguing about?

The fact that you and many other plumbers are lousy at economics and heat transfer. Of course, neither are really meant to be plumbing core competencies so it's not difficult to understand it being a stretch. That's also why the "99% of Being Smart...Is Knowing What You're Dumb At" signature is so ironic in this instance.

I'd go for the 95% efficiency myself....
http://www.bradfordwhite.com/images/...eets/123-B.pdf

That would be great if it was really 95%. However, 95% is AFUE, not EF. By the same measures as for other tanks it will likely be somewhere in the 80% range. I hope it is higher but suspect the base EF of non-condensing of similar config would be about 0.67 @ ~82% AFUE. That would give a storage loss factor of about 0.67 EF/0.82 AFUE = 0.82 storage efficiency loss. 0.95*0.82 would be 78%. I'm anxiously awaiting the Energy Star results of these new units and hope they outperform in the 85% range.

What do you want to bet that it has 2" or more of insulation thickness? I suspect it is 3" or more... That of course is one of the central points about the silly statements by plumbers about blankets doing nothing or not being cost effective. The average consumer tank from what I can tell still has about 1" of insulation.

To give your argument a fighting chance, I'll generously spot you an EF of 0.85 for condensing storage vs an EF improvement of 0.03 for adding a blanket to a 0.58 tank. 150 therms a year is the 1.0 EF factor annual gas use. At 0.85 it would be 176.5 therms. At 0.58 it is 258.6. At 0.61 it is 245.9. The condensing storage saves 82.1 therms a year, impressive! The blanket saves 12.7 therms/year. Condensing sounds like a no brainer.

But there is also the price to consider. Even if you use a high end blanket price of $25 the cost per annual therm of saving is only $1.97. Now, do you think you can get anywhere close to buying a condensing unit for only 82.1 * 1.97 = $161.7 more than a 0.58 EF tank?

How about cost of installation? Cost of installing blanket = $0. Cost of installing condensing unit > $0. Cost of moving blanket from one tank to the next...$0.

Maybe the real reason plumbers hate the insulation blankets and repeat erroneous claims about them is that they don't get paid to install them?

[Redwood]

Continue on!
I'll be hanging out with the others...

[Doherty Plumbing]

But there is also the price to consider. Even if you use a high end blanket price of $25 the cost per annual therm of saving is only $1.97.

So you're arguing that someone should spend $25 to save $1.97 / year and HOPE that they break even on the cost of the jacket over the lifetime of the hotwater tank. Then they need to hope that the jacket fits the next new tank they put in?

If this is the case and I'm reading your statement correctly I'd say there is no sense in arguing with you because you have no sense to argue with.

[Redwood]

So you're arguing that someone should spend $25 to save $1.97 / year and HOPE that they break even on the cost of the jacket over the lifetime of the hotwater tank. Then they need to hope that the jacket fits the next new tank they put in?

If this is the case and I'm reading your statement correctly I'd say there is no sense in arguing with you because you have no sense to argue with.

These engineers just seem to have an endless supply of flawed logic...

Might be best to let him win this argument lol

[Runs with bison]

So you're arguing that someone should spend $25 to save $1.97 / year and HOPE that they break even on the cost of the jacket over the lifetime of the hotwater tank. Then they need to hope that the jacket fits the next new tank they put in?

If this is the case and I'm reading your statement correctly I'd say there is no sense in arguing with you because you have no sense to argue with.

Apparently it is you who lacks common sense and can't read or figure. The cost is $1.97/per therm saved each year...it's a measurement of the investment cost compared to the annual benefit.

That's $25 (max) invested, perhaps as low as $16 (I've seen both prices on R10 and with tax locally they are running $22.50 at the moment). The savings in the example were 12.7 therms per year (could be less or more depending on circumstances so don't get fixated on the value itself, but the magnitude.) So that's $1.97 cost for saving a therm annually. Around here a therm averages about $1 so that's a very fast return, just under two years on the payback. Any safe investment I can make with a reasonable life that returns roughly $1 every year for ~$2 invested is awesome.

Let's say the tank lasts a very short time in the example above, only 6 years. (I've never had a tank go that soon, but there are tanks rated at 6 years.) The savings add up to roughly 12.7 * 1 * 6 = $76.2. That's not too shabby of a return on $16-25. More likely the tank will last 10 years or so. And more than likely the blanket will outlive the tank.

As for whether or not it will fit another tank...it ain't rocket science, it's not welded titanium or specially formed carbon fiber, it's a 48" x 75" piece of insulation. Have you not even seen one, or are you just spreading FUD? The overall tank dimensions are pretty well fixed for a given increment--around 20-22" diameter for 1-2" blown insulation thickness on 40-50 gallon tanks. The lengths covered are also essentially fixed. That's why the standard blankets fit them. A small notch for the T&P and a small cut out for the gas valve/thermostat are the other parts to consider for fit...again nothing that can't be changed/moved later with a utility knife and/or some HVAC foil tape. DIY-wise it is somewhat more involved than changing a light bulb, roughly the equivalent of changing a tire.

So whether or not the blanket can be reused depends on whether or not one is updating to a considerably different type of tank the next time out. That's a possibility if one changes tech, but the blanket I'm currently using would have fit any tank I've had in the past 20 years in five different homes. If one were to go to a tank with 2" foam the benefits of the blanket would be greatly diminished...but if you already have it, and it fits the space, it pays out essentially free money.

Some might be eligible for energy tax credits as well, although since I purchased mine before the credits I have not investigated the possibility.

[Thatguy]

there is no sense in arguing with you because you have no sense to argue with.

Good one. I'll have to remember it. But, it is
ad_hominem.