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Old 12-04-2019, 14:58   #1
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Hot water tank construction

Hi all,

I am soon to build my boat heating system, modeled mostly on ColdEH's excellent boat heating thread from a few years ago.

Hydronic heating. cabin/water

A bit sad to see that I thought I was ready to go back in 2015 and here I am with the bits in my hand in 2019.

But that's life really.

So, I am building the buffer tank, and I have a good place in the boat, a space that otherwise would not get any use at all because it is very inaccessible. To get to the tank in, I will have to remove the stove, but the access to the top is very good, so maintenance will not be an issue.

I am using a 50 liter (11 US gallon) plastic drum with a threaded opening on the top for access, the drum top will incorporate the connections for the feed and return for the coolant water, and the feed and return for the heat exchanger.

My plan is to make a box that fits reasonably snugly in the space available, then I will put the plastic drum inside the box, suspended clear of the base, and then fill the void with two part poured foam. This should give a VERY thick layer of foam around the barrel, a minimum of four inches, and a lot more at the corners.

Does this sound like a workable system? Should I include some kind of foil insulation? Do you think the foam will be enough to support the drum or should I maybe incorporate some timber supports? Is this two part foam even suitable for heat insulation?

Over to the thermo-nerds,

Matt
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Old 12-04-2019, 15:23   #2
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Re: Hot water tank construction

Matt:

Such foam was commonly used "way back when" to spray in around inadequately insulated refrigerators. We used it on our first Insatiable for that, and it greatly helped: the fridge ran for shorter periods of time, and occasionally, we made ice, which it would hold, okay, with a closed cell foam "lid" for the "freezer" section. There's other, better insulation, but the spray in foam is sorta magic.

The foam, where exposed, is sort of crumbly: you can dent it with your fingernail. I think your tank should have timber floors to sit on, but leave space for the foam to work its way in. You can always remove excess if you need access to hoses or ??. It is a major pita.

Good luck with it.

Ann
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Old 12-04-2019, 16:31   #3
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Re: Hot water tank construction

Matt, that kinda foam has the reputation of gradually absorbing moisture, which eventually compromises the R factor. It is also a pretty damn good adhesive, at least in terms of sticking to everything. This means that if you use it directly on the tank, it will be bloody hard to remove if that ever became necessary. It is also tricky to mix and spray without making a mess (I'll describe my experience with it someday when we finally share an anchorage) and the mess is incredibly tenacious. Nasty stuff... if you decide to go that route, do some practice runs off the boat!

Jim
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Old 12-04-2019, 16:41   #4
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Re: Hot water tank construction

I've poured expanding foam into large lightweight plastic bags to help contain the foam and reduce water absorption in past projects. It still moulds to shape around the object without sticking directly to it and it can help with removal at a later date if necessary.
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Old 12-04-2019, 16:51   #5
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Re: Hot water tank construction

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I've poured expanding foam into large lightweight plastic bags to help contain the foam and reduce water absorption in past projects. It still moulds to shape around the object without sticking directly to it and it can help with removal at a later date if necessary.
That's a neat idea! How much room for expansion do you allow? and how do you seal the bags?

Ann
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Old 12-04-2019, 19:36   #6
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Re: Hot water tank construction

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Matt:

Such foam was commonly used "way back when" to spray in around inadequately insulated refrigerators. .... There's other, better insulation, but the spray in foam is sorta magic.
Quote:
Originally Posted by Jim Cate View Post
Matt, that kinda foam has the reputation of gradually absorbing moisture, which eventually compromises the R factor...

Just a clarification, I am talking poured two part foam, not the spray sort. Does that change anything?
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Old 12-04-2019, 19:37   #7
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Re: Hot water tank construction

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Originally Posted by cj88 View Post
I've poured expanding foam into large lightweight plastic bags to help contain the foam and reduce water absorption in past projects. It still moulds to shape around the object without sticking directly to it and it can help with removal at a later date if necessary.
That's easily applied to this job when I think about it. All I need to do is wrap the tank in something as simple as cling wrap before I pour.

Nice one.
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Old 12-04-2019, 19:49   #8
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Re: Hot water tank construction

Quote:
Originally Posted by GILow View Post
Just a clarification, I am talking poured two part foam, not the spray sort. Does that change anything?
I'm not really sure, Matt. The foam used as floatation in some FRP skiffs, etc, is notorious for absorption over time, becoming a soggy mess. It's likely "mix and pour", but there are doubtless many different formulations available. Best to ask the supplier rather than an infrequent amateur user like me.

But the mess warning is pretty universal, I think!

Jim
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Old 13-04-2019, 05:07   #9
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Re: Hot water tank construction

Yes, a bit of googling around clarified the issue of saturation in closed cell foam. Mostly seems to be when the foam is exposed to trapped moisture. Seems like it will not be a problem with my application since there will be no water in contact with the tank (unless things have gone horribly wrong) and condensation should not be a problem with a hot water tank.

But good tip on the mess as you say.
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Old 13-04-2019, 10:03   #10
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Re: Hot water tank construction

Quote:
Originally Posted by GILow View Post
Hi all,

I am soon to build my boat heating system, modeled mostly on ColdEH's excellent boat heating thread from a few years ago.

Hydronic heating. cabin/water

A bit sad to see that I thought I was ready to go back in 2015 and here I am with the bits in my hand in 2019.

But that's life really.

So, I am building the buffer tank, and I have a good place in the boat, a space that otherwise would not get any use at all because it is very inaccessible. To get to the tank in, I will have to remove the stove, but the access to the top is very good, so maintenance will not be an issue.

I am using a 50 liter (11 US gallon) plastic drum with a threaded opening on the top for access, the drum top will incorporate the connections for the feed and return for the coolant water, and the feed and return for the heat exchanger.

My plan is to make a box that fits reasonably snugly in the space available, then I will put the plastic drum inside the box, suspended clear of the base, and then fill the void with two part poured foam. This should give a VERY thick layer of foam around the barrel, a minimum of four inches, and a lot more at the corners.

Does this sound like a workable system? Should I include some kind of foil insulation? Do you think the foam will be enough to support the drum or should I maybe incorporate some timber supports? Is this two part foam even suitable for heat insulation?

Over to the thermo-nerds,

Matt
One remark !!

You are talking of a plastic tank. Bare in mind that coolant water that will heat up your tank in diesel engines usually runs at almost boiling temp. 90 degree celsius. In my boat tank is made of pure copper.

Alex
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Old 13-04-2019, 12:31   #11
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Re: Hot water tank construction

There are epoxy foams that I believe do not absorption water. In the long term any additional cost is likely well worth it. Good luck
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Old 13-04-2019, 12:52   #12
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Re: Hot water tank construction

Why heat and hold water? ........install a Hurricane hydronic heating system with on demand hot water.........I think hoarding hot water is so last millennium.....
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Old 13-04-2019, 13:04   #13
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Re: Hot water tank construction

You can try this one:

http://www.vc-24.com/index.php?id=4&...7bfa7c80014a17

91% closed cell....
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Old 13-04-2019, 13:45   #14
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Re: Hot water tank construction

If you do go forward.........think a 50 kg drum trying to move around in tune to your sailing movement........yeh suspending and pouring not such a good idea without LOTS of bracing.....otherwise over time it will pound away and crush the foam then want to visit the galley at the wrong time mid passage somewhere.....fuel and water tanks are always strapped in so they don't move.
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Old 13-04-2019, 14:04   #15
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Re: Hot water tank construction

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Why heat and hold water? ........install a Hurricane hydronic heating system with on demand hot water.........I think hoarding hot water is so last millennium.....
Unfortunately my budget is last millennium too. Sometimes innovation and applied effort have to replace cash.

And I like building things.
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