Insulate the Wet Return?

EF_4

I there any reason to insulate the wet return in a steam pipe heating system?

Norm Harvey

Generally you dont need to insulate after the main vent. The main vent is on the end of the line and at that point you dont care if the steam condenses.

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EF_4

How about insulating . . .

the risers inside the home or apartment?

And I assume that when we speak of insulating the main that also includes the branches from the main to the risers?

DanHolohan

Yes,

as water cools, it absorbs carbon dioxide and forms carbonic acid, which eats wet returns. The water you keep the return water, the longer the pipes will last.

The Wire Nut

Different Reason . . .

Thanks. Although I was told a different reason for keeping the water in the wet return as hot as possible.

William Faust

strictly for energy costs

You could insulate returns with result that boiler would have to fire less. If you have a pumped system, however, you would want to make sure that the condensate is not too hot (from bad steam traps); otherwise, the pump will cavitate.

The Wire Nut

Size Insulation?

And is there a standard accepted size for insulation of the main? My main is 2.5"

Brad White_9

At least one inch

Most state model building codes dictate one-inch thick insulation for 141 up to 200 degrees and for that pipe size (up to 4-inch pipe size -This is per Mass. Code, FWIW).

Naturally if all you have available is half-inch HD grade, it is better than nothing. One inch will take your heat loss down to about 1/6th that of bare pipe. Half-inch will take it down to about 1/4th to 1/5th so it is not such a bad thing if the thicker stuff will not fit or is not immediately available.

Use fiberglass though, not foam unless the high temperature stuff from Armaflex.

The Wire Nut

1\" v 2\"

Actually, I was thinking whether it needed to be more than 1" insulation. Someone told me to use 2" on the main. And I didn't even think about what the local code requires as a minimum.

Brad White_9

Your codes may vary

On the returns, one-inch would be fine and would meet code. Not sure that thicker insulation would buy you much; call it the law of diminishing returns. The first inch cuts the heat loss to about 16% of what bare pipe was. Double that insulation -add another inch- and you cut it in half (meaning another 8% saved). Add another inch and in rough terms you cut another 33% of the remaining 8% or another 2.6%... See what the first inch does compared to the second? Not saying "don't use thicker insulation", rather just see what the cause and effect is, if heat conservation is your goal.

On 2" steam pipe, 2-inch insulation is stipulated.

This is not to say that less will not work "OK" but the codes are there for a reason.

Prompted by a question some months ago, I looked into the difference of various thicknesses and given the cost of the thicker stuff, the choice to recommend a greater thickness over an inch based on economic factors only was not so simple nor clear. That is why I love this place- always learning something new.

The Wire Nut

So 2\" for the main . . .

is what you're saying as far as insulating the main.

Brad White_9

Yes

Snug as a bug in a rug.

The Wire Nut

Thanks . . .

for all of the info. Looks like the time has arrived to put this thread to rest.

Brad White_9

Yes, lack of insulation leads to heat loss which causes...

oh never mind!

JJ_4

non-insulated returns

My one pipe system is 84 years old. Other than a replacement boiler (coal to gas, new isolation valves, and new vents, the system has never been modified. It was installed with no insulation on the returns.

Ten years ago I had to replace a 12 ft section of wet return and this year I replaced the remaining 24 ft. The other return (the system splits front/rear of the house)drops down right at the boiler and isn't wet.

I think I'm good for another 74-84 years. I'll let my son know to tell my yet to be born grandson that he'll have to do this maintenance someday.