Hi, We're installing a radiant floor heating system and had a couple questions about install. Heat loss was done and all zones mapped out but not the actual panel where everything connects. So first question was, we have 2 temperatures, so will be using 2 mixing valves to lower temp from existing boiler and am unsure sequence to put them in. There will be 2 manifolds of 7 loops of one temperature and 1 zone on other temp. Can't seem to find many people in my area who do radiant and can't get any companies to help via internet without paying them all kinds of money to do their own heatlosss which I already have done and dont need. Anyone that can help would be greatly appreciated. Secondly I want to make sure boiler is protect from flue gas condensing, any ideas? Thanks for the help.

The reason hydronic designers want to do their own heat loads is because of experience.

Have you done a heat load for each room? each manifold? Is this a cast iron gas-fired boiler? You will have to tell us what the two manifolds are hooked up to. What is the load and the output of your emitters?

I wonder how you came to the two design water temperatures? The controls and near-piping are the rub on any hydronic system as there are many ways to do it (most of them not optimal).

I had a local guy do the heat loss, but wanted to do install myself. Each room heat load was done. Yes it is a cast iron gas boiler. Right now nothing is hooked up and I don't have all the parts, that what I was looking for help with. Around here the few people who do it all use a certain manufacturers products and only that manufacturer so a lot higher price on some things. Two water temps came because one zone had a high heat requirement so a fairly large difference from rest of rooms. I was hoping to have someone look over the heat loads and possibly provide a diagram for hookup and parts list. I understand each guy wants to do their own heat loss but there shouldn't be that much difference from one to another if its done properly.

" I understand each guy wants to do their own heat loss but there shouldn't be that much difference from one to another if its done properly."

I couldn't agree more!

In fact it is hard to explain to my local customers here in Minneapolis (many of which are engineers of one sort of another) why the five professional heating contractors that proceeded me, all came up with a different load. The answer is education, experience, software and due diligence. Once the heat load is established manufacturers specifications are used to size the radiant panel, panel radiator or emitter whatever it be, for each room. If you have existing cast iron radiators, they too may be sized according to established guidelines, resized for lower water temperatures and a design water temperature specified matching potential output to the actual room load.

As to your problem; protecting the boiler is first and most often, if crudely, done with a simple bypass. In multi-zone, multi-temperature hydronic systems, this approach will result in unsatisfactory results. My choice is a mixing valve with outdoor reset and boiler return water protection.

Second, I look to the coldest room and the lowest output emitter (why they are always in the same room, I can't say).

I like to design hydronic systems for older homes using a single design water temperature (the average water temperature needed to satisfy the thermostat on the coldest day of the year) and adjust my radiation to fit. I do this by adding panel radiators to radiant panels and installing thermostatic radiator valves on old cast iron radiators for perfect room control. As I use condensing boilers almost exclusively, outdoor reset allows for the lowest and most efficient water temperature while increasing comfort. The radiation is warmer more of the time just keeping up with heat loss.

This perfect comfort can be achieved with ODR controls added to an existing cast iron boiler with considerable fuel savings and matching comfort but without the 40 to 50% fuel savings of the condensing boiler on such applications.

When using mixing valves I most often use them to limit temperature downstream of a mixing valve, for instance when mixing a low temperature radiant floor with fin-tube. But on a recent sub-floor system with plates the floor lagged so far behind the wall-to-wall fin tube, the fin had to be shut down to better balance the system.

In other words, mixed radiation with a conventional boiler isn't easy...but you already guessed that.

If I heat the one zone that has much higher temp with a different system(baseboard possibbly), then all my temps will be same and make life much easier. If only one temp now, would you still recomment mixing vavle with ODR?

ODR is a bare minimum for most normal temp radiant systems' proper operation.

I can say I concur with everything morgAn has said here. Our own experience with external heat losses is at least 3/4 of them are what we would consider to be very high, and it takes almost as long to do a survey of another person's work as it does to simply do the work ourselves. If we do it ourselves, we can ensure good results, so it only makes sense to avoid the potential for additional finger pointing.

Thank you kindly Rob.

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