Super interesting, Thanks for the info! So for condesnsing boilers, what would be better than a retrofit, radiant floor? Is there a type of baseboard radiator for condensing boilers that are more efficient than the retrofitted radiators/basboards mentioned?
I did not put in my post because it was alluded to in an earlier post -- the "condensing" occurs when the cool return water is used to cool the exhaust gases -- this extracts heat from the hot flue gas -- heating up the returning water before it goes back to be reheated in the boiler. Doing this produces water -- that's why condensing units require a pump/ drain. The water come out of the flue gasses
A typical non condensing boiler (furnace) sends the very hot flue gases up the flue/vent/chimney -- the water is taken with it.
Yes -- radiant is great for condensing boiler s .. because it uses lower temp water.
As Jackfre mentioned -- there are other types of radiators that can be used.
Example: For the house I mentioned above in Chestnut Hill. The entire heating system was over sized ... originally a coal fired boiler. All the radiators when supplied with 180 degree water would over heat the space. Two ways to control the system -- thermostats on the wall making an on/off situation ... or having each radiator w/ a thermostatic head that allowed water to flow.
A third way occurred when outdoor reset became available: you can now send cooler water throughout the house continually. Instead of making 180 degree water on a 40 degree day .. you make 130 degree water .. or 120 degree water. Whatever is needed ... the boiler's water temp is controlled based on the outside temp. It takes a little trial and error but eventually you can actually match. A modern wall boiler can modulate the gas fired to achieve the temp ... the old school cast iron fires on and off keeping the water temp constant.
When cooper fin baseboard became the norm -- the installer would do a heat load and factor the amount of baseboard based on the water temp. Well -- you can do many feet less of baseboard at 200 degree water vs 160 degree water ..... what do you think got installed? It was cheaper and the installer made more money putting in less feet and cranking up the boiler. But you can read the tables and they will show you how many feet to install with 150 degree water .. etc. Copper baseboard can be sized to be continuous w/ outdoor reset.
On of my projects was a deep retrofit where much of the heat was underfloor plates -- not as efficient as slab or some other floor systems. I figured we would run 130 - 140 degree water on cold days. So in the spaces that I could not do radiant -- or that would not get enough heat from the floor (too many windows/ old plaster stone walls) I added panel radiators .... factoring the output at 140 degree water. IE: I installed larger panels.
My newest project is almost all radiant (warmboard/slab/ a few panels) -- the goal is to try to use all the same water temp. With a wall condensing boiler and outdoor reset I shod be able to run low temp water most of the time .. condensing. This house is propane ... so the fuel cost is greater .. it's also larger 5k+. I'm not using a combi -- it will have an indirect.
Combi units add the issue of hot water .. it's no different vs an "on demand' unit. It is an "on demand" unit. They work great in some applications. But again -- it just hot water. If you need huge amounts of hot water -- I use one for a dedicated outdoor shower at my beach house .. they are great. It may not give you anything if you are a typically household w/ NG -- a tank or indirect is hard to beat. Sometimes rebates make the difference.
