Buffer Tank glass-lined vs stainless, sizing

wcs5050

New to the buffer tank game, but definitely see the advantage. I’m seeing some sizing calcs here and there… doesn’t seem like a huge volume is needed. Can anyone weigh in on the glass-lined vs stainless choice? I feel like with properly treated, oxygen/air free fluid the glass will endure far better than in a DHW situation. If stainless is only a bit more cost, why not. Thanks.

wcs5050

I’m primarily concerned with connection to low mass, modulating boilers for the moment.

I’m thinking with air to water heat pump connection, bigger buffer tank is better? Merely guessing.

hot_rod

Plain steel works on a closed system. I've used air compressor tanks, LP tanks for buffers also.

But scratch and dent water heaters are cheap and easy to come by. I find electric water heat tanks on FB marketplace for around 150 bucks.

There is a number of criteria for sizing. Cycling, storage, space availability, cost, etc.

The loads and the equipment you have or are considering is the determining factor.

Buffers for HPs are getting smaller as the compressor modulating gets better. At least one brand promotes buffer-less HP piping.

On the boiler side, look at the smallest zone BTU, and the lowest turndown of the boiler to help decide. Some formulas in this issue.

https://www.caleffi.com/sites/default/files/media/external-file/Idronics_17_NA_Thermal%20storage%20in%20hydronic%20systems.pdf

wcs5050

Very good HR. Thx for the intel!

I had considered electric tanks but thought the 3/4 taps would be a choker. If the flow math works then probably fine. I guess on the glass lined vs stainless I was wondering if it’s worth worrying about upgrading to stainless for longevity. I suppose the stainless option might just be an upsell.

I have a decent size job coming up that will absolutely benefit from a buffer tank, but I’m considering options for my own home that’s being served by a late 90s series 2 with Tekmar 256. It’s a dependable workhorse but I’m finally thinking about a modulating solution.

What about the old series 2 as a buffer? Haha.

Thanks again.

hot_rod

Make the size increase short and close to the tank. You get a slight velocity increase through the increaser.

I've taken 3/4 to 1-1/4" on tanks 12- 14 gpm possible.

Here are the fittings I have used on HW tanks.

3/4 mip to 1-1/4 copper adapter use on the water connections

3/4 x 1-1/2 stainless bell

1" mip x 1-1/4 copper use for the element holes

1X 1-1/4 brass swage nipple

Swage nipples were used in Munchkins as their header was 1" connection. So some were 1X 1-1/4 and some actually were 1 X 1-1/2" nipples! I think the 199,000 had the 1X 1-1/2 swage nipples

On this 6 gallon tank, the 3/4 water connections are increased to 1-1/4 for the LLH function

Stainless tanks? How are your chloride levels?

Glass lined seem to be able to handle most any water condition. Keep them under 180°F. High temperature, thermal stress, is a killer on glass DHW tanks.

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Big Ed_4

For longevity I would lean toward glass line . Stainless tank makes sense . Welding stainless is difficult which , Which brings up the percentage of an issue …

Kaos

With any setup, it is generally best to design the buffer tank out. There are many ways of limiting cycling, I would look at those options first. No buffer tank (less $), no chance of mixing (better fuel efficiency) and takes up less space.

For example on my AWHP, I can use the primary loop itself as a buffer volume. Stores enough heat to support defrost and limit cycling in warmer weather.

hot_rod

It doesn't take a lot of tank to hold hydronic pressure and temperature. An expansion tank for example is sheetmetal.

I built a solar drainback tank from a Harbor Freight air tank.

Heck a .11 mm aluminum Coke can, about the thickness of a human hair, can hold 90 psi!

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