Pipe Insulation Advice

David Nadle

According to the thermal data I got from Knauf, the marginal benefit to 1-1/2" or 2" insulation on my 2" mains is small, while the extra cost of the thicker insulation is not small at all.

[EDITED -- ORIGINAL POST HAD INCORRECT DATA]
At 200 deg. operating, 80 deg. ambient, 1" insulation reduces heat loss 86%. 2", 91%. Surface temp is 93 deg. vs. 86 deg. Meanwhile, the 2" insulation is 2.6 times more expensive. I'm not sure if the model energy codes take that into account.

There is also headroom in the basement to consider, and the increased likelihood of having to squeeze thicker insulation around nearby obstructions.

Brad's point about grooved returns is interesting but insulation seems like a pretty expensive way to guard against what must be a very slow process of pipe corrosion.

AG

A few questions

I have a gas-fired steam boiler with piping that ranges from 2.5" to 2" to 1.5" up to the radiators. I have only owned the house through one winter and it was really inefficient. I have researched and it looks like the first thing I should do is insulate the pipes since they are not insulated. It is a one-pipe system and it looks like iron pipes, so I have a few questions:

1. Do I just insulate the supply piping? or is it necessary to also insulate the return piping?

2. I looked at insulation options at Home Depot and a couple of local plumbing/heating supplies. It looks like my readily available option is fiberglass insulation. Home Depot and a few locals carry the half inch thick insulation. One local has a 1" thick that is a little more costly. Any recommendations on how much better the 1" may be?

I welcome any advice. Thank you.

Big Ed_3

Advice

You only need to insulate the supply piping . The 1" insulation is best .

Brad White

Respectfully

I have to disagree with Big Ed, in part.

Where I do agree is that 1-inch insulation is a minimum, will work well and that the 1/2" thick stuff in the Big Box Stores is best left to insulate those shelves.

Many model energy codes prescribe 1.5" thick for up to 1.5-inch pipe and 2" thick insulation for piping 2-inch to 4-inch sizes.

But if 1-inch is what you have, so be it. It will cut the bare-pipe heat loss to about 1/6th of what it was and is a good value.

Where I disagree more is the advice to insulate only the mains. Yes, do those, but also insulate the returns.

I used to advise to do so as an option, but the tendency for the cooling condensate to absorb CO2 and create carbonic acid which will groove the piping, convinced me to insulate the returns too. 1" is OK for that.

Brad White

All very good points, David

Thanks for adding them. I agree, the thicker insulation jumps beyond proportion and the energy codes as far as retrofit applications, is self-policing. No one but you will turn yourself in to the Energy Police.

Agreed too, the energy codes do not always balance a true cost-benefit equation in all areas. A personal friend chaired the Mass. Energy Code committee some years ago and I was impressed to see how the panel had representation from across the spectrum of contractors, energy experts, architects and even homeowners. A weighted code meeting at least a concurrence was achieved.

I have not seen data to support the 94% reduction numbers- my data says about 84% and yes, the additional 0.50 to 1.0 inches is an exercise in diminishing returns.

Speaking of diminishing returns.... to me it is all about longevity and an inch or even a half-inch of insulation on the returns is money well spent for a system that should last 100 years. If the piping is to be concealed, say below a finished, I would insist on it. Short money as it may double the life.

JohnNY

Good information, David


At 200 deg. opertating, 65 deg. ambient, 1" insulation reduces heat loss 94%. 2", 96%. Surface temp is 72 deg. vs. 68 deg.

Could you link to the page detailing that information. I can't seem to find it.

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David Nadle

Oops...used the wrong table.

Using the most appropriate table from Knauf this time: at 80 deg. ambient with 1" ASJ insulation, heat loss for 2" pipe is reduced 86%. 2", 91%. I still don't think that justifies the extra expense. It's 6% better for almost three times the cost.

Brad White

No question

the extra material cost cannot be justified (three times? Wow. It has been some time since I checked).

This discussion does underscore an old maxim, that "the first inch does most of the work". Absent banging from steam collapse and general thermal fitness and in working out the numbers some time ago, I am "soft" in insisting on thicker than one inch but am compelled to mention the energy codes. My cynical side says that energy code mandates drive the cost up although I imagine the extra thickness does cost more to make, could it be that much more?

My data is from the insulation manufacturer's association (I forget the exact name) but they do have a free-ware insulation program based on your target goal (energy savings, personnel protection, etc.)

All good information indeed.

David Nadle

Link to PDF at Knauf

Here's the link--but I used the wrong table in my first post. Use the one for ASJ insulation, not metal jacket.

http://www.knaufinsulation.us/pdf/Pipe%20Insulation%20Thermal%20Data%20Guide.pdf

David Nadle

The extra cost makes sense.

If you compare the cross sectional area of the 2" insulation vs the 1", it's 2.6 times more material, therefore 2.6 times the price.