Livin’ in the USA

Some people call him the Space Cowboy, some call him the Gangster of Love. But Steve Miller’s always lived in the USA…

Great rocker from – are you ready – 1968!

So far this month, we’ve learned why Europeans primarily install panel radiator systems with TRV’s (click here to review) and, as a result, why European-designed circulators typically have low-flow, high-head, steep performance curves (click here to review).

Quite simply, the most practical installation method bred a circulator designed to match the system requirements.

Why, then, is the classic “American” style pump curve a high flow, low head, flat curve?

Same reason.

In older cities, the next-to” communities started growing in the mid-to-late 1800′s due to new transportation technology – electric street cars and that new-fangled “horseless carriage” made it easy to live out there and travel into the city to earn your daily bread.  If you’ve ever worked in any of those older homes you’ve seen amazing old heating systems, mostly  steam or converted gravity systems.

These home had lots of heat loss (therefore lots of flow) and big pipe (therefore very little head loss).  Fast forward into the 30′s and what homes that were being built during the depression (with enticements from the newly formed FHA) had either 2-pipe hydronic systems or venturi-tee systems.

Reading through the B&G Hydronics Design Handbook published in 1940 is fascinating – a design example shows a venturi-tee system requiring 12.5 GPM (120,000 BTUH, using their math) with an estimated 4′ of head.

High flow, low head.

Look and compare:


After WWII, VA loans made buying a home in the suburbs less expensive than renting an apartment in the city.  And new tax laws allowed homeowners to, for the first time, deduct mortgage interest from their taxes.  It was a perfect storm for suburbia to explode.


And explode it did.

You all know the story of Levittown, but similar communities were sprouting all over the country. And many of those homes had hot water heat with venturi-tee systems or two-pipe systems with cast iron baseboard, radiant floor heat or another new-fangled development: fin-tube baseboard zoned by circulator or zone valve.

These homes shared relatively speaking high heat loads, and since the design standard of the day was a 20Delta-T, the required flow rates were high.  But since the pipe was large (¾ or 1″ copper or black iron), the head losses were fairly low. Here’s an example:

100,000 BTUH = 10 GPM

Biggest zone = 40,000 BTUH or 4 GPM

Length of biggest zone: 120 feet

The head loss of  ¾” L tubing (most common back then) at 4 GPM is .04′ of head per foot of pipe.  If the adjusted length (taking into account fittings, valves, etc) of that longest loop is 160 feet, then the overall head loss would be:

160 feet × .04′ of head per foot of pipe = 6.4′ of head.

So if this were a zone valve job, we’d need a circulator capable of 10 GPM at 6.4′ of head.

Again, ideal for a high flow, low head, flat curve circulator, no?

Bottom line: both in North American and in Europe, circulators were developed to work in the systems most commonly installed in those markets.  There’s nothing inherently better about a high head circulator or a low head circulator.

The best circulator is the one that fits the job you’re working on.

As we  continue this series, we’ll discuss what can happen when you stick the proverbial square peg into a round hole.

Gotta hand it to ole Stevie — he’s an American Original…

And just to make you feel old, Steve just turned 70 last fall.

“Same old story with a new set of words…”

Leave a Reply

You must be logged in to post a comment.