Redoing existing system

Heat Source?

Is a boiler better then a water heater - YES, significantly more so. Boilers and their heat exchangers are built much more robustly than a water heater.  They also must adhere/meet higher standards in most cases.

The problem with older systems is you can run into all sorts of products, controls, and "deviations" from the norm of how it is supposed to be done (or could be done).  This may scare some guys away and I can see why one person may have wanted to work with your exisiting controls, the other preferred not to. Having said that a serious hydronic guru can usually pick up the pieces and see the similiarities in most systems to current offerings with a different badge on it.

As to if you can use one pump for the entire system, well it depends. What type of boiler do you have? Electric? Gas? Oil? Propane? Is it a conventional boiler or a condensing boiler?

I'm going to go out on a limb and bet it's probably a conventional natural gas boiler in which case  you'd want 2 pumps at a minimum pumping through a 4 way mixing valve. A 4 way mixing valve is one design/installation method that allows a conventional (high temp) boiler to work with a low temp load. It protects the boiler from cold return water (which is what radiant floors give) and it protects the radiant floors from the very hot supply water from a conventional boiler. It does this by mixing a little bit of the hot supply water from the boiler with the return water from the radiant floors to achieve a moderated, temperated water temperature to heat your radiant floors, while at the same time, mixing even more hot boiler water with some of the radiants return water, to send moderated, hot water back to the return of the boiler to protect the heat exchanger from flue gas condensation.

If you send cold return water to a conventional boiler for a long period of time it will cause the heat excahnger to condense. This will over time eat the heat exchanger and cause it to fail prematurely. If you send too hot of water to the floors you can do all sorts of things - from warp or crack floors, to unbearable floor temps, the list goes on...hence the requirement of a control method that accomodates the requirements of a conventional boiler and radiant floors.

Typical conventional boiler supply temps are 140-180 degrees with the general rule being you do not want to send water any cooler than 135 degrees back to the return of the boiler.

Radiant floor temps, depending on the designed heat loss and radiant panel design, as well as the floor coverings (e.g. hardwood, carpet) typically top out at about 140 degrees or less supply temp- the key being you don't want the finished product i.e. the floor temperature to be more than say 85 degres (these are fahrenheit).  85 degrees, again is the finished product. You could send 140 degree water to the floors but only get 85 degree floors if you have thick carpet which requires warmer temps to drive the heat through.

There are a myriad of ways to work with the attributes of the heat source and the heat distribution I described above but you will need at least 2 pumps. For a 4 way mixing valve - 2 pumps, primary secondary, 2 pumps, 3 way mixing valve off of a primary secondary, 2 pumps, Injection mixing, 3 pumps. So 2 pumps minimum for any of the systems I described.

Typically, you have at least 1 pump for the heat source, and 1 for the distribution.



For the distribution, you can zone with either zone valves (or actuators which are basically just zone valves for each loop), or pumps. In this case you could have 1 pump per zone, or 1 pump and 1 zone valve per zone, and when 1 zone valve opens up, it turns on the pump on a call for heat.

I apologize for bastardizing the word pump - in a closed system it's actually a "circulator."