Help with number of pumps for retrofit radiant floor system

softieroberto

Hello, I'm retrofitting radiant floor loops into an existing system with an old boiler and cast iron rads. I'd like to separate out the floor loops with a heat exchange.

I'd love some guidance on whether the pump on the boiler side of the heat exchange is enough to pump water through the CI rads and the heat exchange. Would also love any suggestions if you see any other mistakes. Thank you!!

Big Ed_4

Why the use of the heat exchanger , are we talking about a snow melt system ?

softieroberto

Big Ed_4 said:

Why the use of the heat exchanger , are we talking about a snow melt system ?

It's just for radiant floor heating. I was thinking that since the CI boiler, steel piping, and CI radiators are 100 years old, and I've seen a fair amount of dirty water in them when I empty out the system, that I don't want that contaminating the new radiant floor loops. When I have the budget, I'm going to upgrade to an air to water heat pump and will lose the heat exchanger.

But maybe I don't need it even with the old piping/boiler/rads?

Big Ed_4

A aged hydronic system will build up black water , that aged water is great for heat transfer . Ongoing leaks are bad , slab leaks . Chunks of iron , red rust should be a concern .

The heat exchanger may be an over kill .

softieroberto

Big Ed_4 said:

A aged hydronic system will build up black water , that aged water is great for heat transfer . Ongoing leaks are bad , slab leaks . Chunks of iron , red rust should be a concern .

The heat exchanger may be an over kill .

Thanks. I have no existing leaks. If I remove the heat exchange, then where would the pumps go? Would I need 3 -- boiler return, radiator manifold, and floor loops? What are the principles I use to guide this decision?

Jamie Hall

Nothing wrong with "dirty" water. Now if there are particulates in it, you need a filter anyway.

And what you do need is first, everything must be piped in metal or oxygen barrier PEX. Don't skimp on that. Then the radiant loop pulls off the main system, treating the main system as the primary loop and the supply and return from the radiant as secondary, with closely spaced Ts in the usual way. The radiant loop, however, has the supply from the main loop feeding into the hot side of a mixing valve and a line from the return from the loop feeding into the cold side, and a secondary pump pulling from the mixed outlet to feed the loop. The mixing valve is set for the temperature you want in the loop.

Simple.

softieroberto

Jamie Hall said:

Nothing wrong with "dirty" water. Now if there are particulates in it, you need a filter anyway.

And what you do need is first, everything must be piped in metal or oxygen barrier PEX. Don't skimp on that. Then the radiant loop pulls off the main system, treating the main system as the primary loop and the supply and return from the radiant as secondary, with closely spaced Ts in the usual way. The radiant loop, however, has the supply from the main loop feeding into the hot side of a mixing valve and a line from the return from the loop feeding into the cold side, and a secondary pump pulling from the mixed outlet to feed the loop. The mixing valve is set for the temperature you want in the loop.

Simple.

Makes sense -- thank you!

softieroberto

Jamie Hall said:

Nothing wrong with "dirty" water. Now if there are particulates in it, you need a filter anyway.

And what you do need is first, everything must be piped in metal or oxygen barrier PEX. Don't skimp on that. Then the radiant loop pulls off the main system, treating the main system as the primary loop and the supply and return from the radiant as secondary, with closely spaced Ts in the usual way. The radiant loop, however, has the supply from the main loop feeding into the hot side of a mixing valve and a line from the return from the loop feeding into the cold side, and a secondary pump pulling from the mixed outlet to feed the loop. The mixing valve is set for the temperature you want in the loop.

Simple.

Sorry, one more question. I left out important info. The old cast iron rads will be used as "second stage" heating only when it's cold. So the radiant floor loops will be on the most. Does that change anything in terms of what the primary loop is and whether the radiant loop should be on closely-spaced tees off of the primary?

Jamie Hall

Shouldn't. Makee sure, though, that when the CI stuff is off that there still is enough flow through the boiler to keep the boiler happy.