Can I use my exsistin boiler for my baseboard heat to run radiant floors?
Discussion Forum
Discussion Forum
Up Next
Video Shorts
Featured Story
There's a constant source of clean water for you to use, and all you have to do is collect it.
Featured Video
How to Install Cable Rail Around Wood-Post CornersHighlights
"I have learned so much thanks to the searchable articles on the FHB website. I can confidently say that I expect to be a life-long subscriber." - M.K.
Replies
Yes, you can but..... a few questions and comments are necesssary.
Is this radiant floor area existing that you are coverting from baseboards or is it new in an addition?
If new addtional floor area, you'll have to determine if the boiler will be large enough to handle all loads. Will the nozzle have to be upsized or is a new boiler in order. How do you heat the domestic hot water (DHW)?
Assuming the boiler is large enough for all loads and the DHW is from an immersion coil in the boiler, you'll have to choose a way to bring the heating water for the floors down to the 95-105 *F range. Until we hear whether you're converting from existing baseboars to radiant or adding new radiant to existing existing boiler, I won't go any further as it wil get too tangled to talk about both, not knowing what your true situation is!
This is an existing house with baseboard heat. DHW supllied by the boiler. Realy Just a gemeral question about a house I am looking at. The bases take up a lot of room (wall space) in a small house. Great garage awsome lot small but aforable house.
Baseboards use water at much higher temps than floors, usually something like 180 degrees for base and 140 for floors.
If you are doing both with one boiler, you need to have a way of supplying both temperatures, such as a tempering valve that reduces the 180 boiler water to 140 before it goes to the floor. A radiant contractor could work out the controls for you.
If you are going to do floors only and no baseboards, then you just turn down the boiler to the lower temp.
I'm fairly experienced with this stuff but would not do much of it myself. Radiant is a very technical area and the guys who do it all day every day are the people to call. If you proceed you should hire a radiant contractor.
The radiant water temps are a bit lower, about 95-105. If the floor gets warmer than 82-85*, the feet don't like it!!!
I have installed and lived with radiant floor, and ran 140 in my staple up system. Floor was about 85 degrees and just right.
Makes me curious. What's above the tubing and what type of insulation/r value is under the tubing? age of house and air tightness?
Older single story home in a moderate climate, I remodeled everything and it was well insulated with good windows. 1/2" tubing installed 8" OC under 7/8" fir plank subfloor and 5/16" oak strip. Most areas with radiant foil insulation and 5-1/2" fiberglass under the tubing but with a 2" air space. Set the boiler to cut off at 140 and return water was a very consistent 135. I used a HyrdoTherm HC-1 boiler, about 82% as I recall, should have used a more efficient unit, that's my only regret. All the control stuff and circulators were Taco.
This is a very typical retrofit install ("staple-up" although I did not use staples) and I did a ton of research before installing it. A radiant contractor (and cycling partner) did the heat loss and spec'd all the parts. The "Wall" is a very useful website for anyone interested in hydronic.
In a slab you might go lower on the water temp, I'm not sure. I'm going to pour a slab for my shop this winter and need to get my design together for that system.
Water temperatures for radiant can vary from 75 degrees to 160 degrees depending on loads, flooring and tubing installation methods.At the higher end of the spectrum though, you're missing a lot of potential benefit.Do NOT turn down your boiler below 135-140 unless it's a condensing boiler. You will rot it out quickly otherwise. To do lower temp radiant (highly recommended) off a high temp boiler you need to add a mixing system of some kind. You will probably also need boiler protection unless you put in a weak, high temp radiant system. The good news is, the controllers used to do the GOOD mixing also incorporate a ton of boiler control features which can really jazz up your boiler performance.. but this is easiest if your DHW is in a seperate storage tank heated by the boiler, not with a coil in the boiler.Once you know your loads, your flooring and your installation options, then you can figure out what needs to be done to control it properly.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Pardon my ignorance but what is a condensing boiler and why would lowering the temp on a non condensing boiler cause it to "rot"?
Wouldn't a mixing system incress the volume of fluid in the system? and if so where would the extra go?
Chardo
The mixing valve doesn't introduce new water to the system, but mixes the cooler return water with the water coming direct from the boiler. I just recently installed an outdoor wood boiler onto my existing radiant floor system in my house, and plan to add my woodshop radiant floor to the system also. Right now, my incoming water from the boiler enters the house at about 170-175 degrees. The mixing valve lowers it to about 135 when it first enters the staple up radiant loops,{below wood plank floors and tile}. The flooring is reading about 85-90 degrees. It also circulates in my basement floor slab. When I tie into my woodshop I anticipate having to re-adjust mixing valves a little bit. That is a concrete slab area, on a seperate loop from house. I kept my existing propane fired water heater that served as my boiler hooked up as a backup. So far, it's worked great.
no problem at all. If a "regular" boiler is turned down too low... or if too much cool water comes back to it... its flue gases can condense. This causes corrosion and rots out the boiler, sometimes very quickly. For this reason most regular boilers need to operate at 135-140 degrees as a minimum... which is much hotter than many radiant systems need.For *any* system to give excellent comfort, it should be run at the minimum temperature it can be, just so you know.A condensing boiler is one of the new generation of boilers out there that not only doesn't mind condensation, but is built to take advantage of it.. it extracts additional energy from its flue gases using condensation. Run at low temperature, these units can easily hit mid to high 90's in efficiency. Plus, most of them have outdoor sensors fairly cheap, which makes the whole unit figure out how hot it really needs to be depending on how cold it is outside, which does *great* things both for its own efficiency, and the comfort of your system.A heating system is "closed", so no new water gets in. Mixing is achieved through different piping practices.. it's called primary/secondary piping, and basically you have a hot side (primary) and a cold side (secondary) that are only attached by a mixing valve, or by an injection pump that can push a little or a lot of hot into the cool. this does send some of the cool water back to the boiler along with whatever hot water was not mixed into the cool loop, so care must be taken that the boiler is protected from the water going back to it is not TOO cool... many mixing controller have this feature built in though, so it will both mix your radiant and protect your boiler.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Quote: "If a "regular" boiler is turned down too low... or if too much cool water comes back to it... its flue gases can condense."
Couldn't you raise the the flue gas temp a bit by sacrificing a few points of efficiency?
We had to have oil burner techs do that here when some of the mid-eff furnaces were being tuned to 88-89%. The flue gas temps got down to 265-280* F and being dumped into exterior cold chimneys. Here it condensed and in one case I consulted on, the condensation ran through the liner and brick joints both and caused staining at the baseboard at the interior wall!
Our national oil appliance installation standard (Canadian Standards Association B-139) now has a chart that all furnaces, boilers, stoves must meet for exiting flue gas temps and liner size. It depends on the BTU input, chimney height, insulated or uninsulated chimney. The flue gas must be measured just before the chimney breeching and not at the test hole used for the efficiency test.
Honestly, I'm not a boiler tech, so I couldn't say. I *believe*, though I may be incorrect, that the problem w/cool return water temps is flue gases condensing on the cooler portions of the boiler itself. I'm not sure if that can be rectified by simply making the flue gas hotter... and anyway, the whole idea of tuning a boiler to dump MORE heat into the flue just makes my skin crawl, especially when the alternative is spending some dollars... not an exhorbitant amount, but making an investment... and adding a controller that will substantially increase efficiency instead of reducing it. And that can do so while maintaining proper minimum temperatures.I think you make a good point though, and not every boiler can have a proper control effectively retrofitted.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com