Anyone here have experience with retrofitting hydronic radiant heat? I'd like to get rid of my forced air system. I have access to the floor joists from the basement.

Really interested in knowing if it's worth a damn?

I have designed a few remodels where the client added hydronic heating after the fact. The biggest problem is what type of flooring is ABOVE the radiant flooring. It takes A LOT of energy (and loss) for that heat to heat not only the subfloor, but also the materials above. Tile is a GREAT receiver of radiant heating, and probably the only flooring I'd use on a retrofit.

The biggest complaint I have heard (besides the labor and time intensive install) is that you can feel the temp difference at the joists. The heat doesn't do well spreading laterally into the area above the joist, so it's a repetitive hot/cold/hot/cold. This may play havoc if you have real hardwood floors too.

Good info, thanks.

I do have 60 year old oak flooring, was wondering if there's a risk of buckling with the increased expansion/contraction that heating it directly would cause.

We had a hydronic system in our condo. It was awful because it shared the hot water heater with our regular hot water. Lots of cold showers in the morning. And the heat wasn’t much. Thankfully, we had a gas fireplace to heat the condo. And I found some nice mica space heaters and plug-in thermostats for the bedrooms.

If you’re going to do this, make sure you have a sprite boiler. And keep your expectations low.


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edogg not sure if your system designer failed here or you just went cheap??? good hydronic system will never run out of hot water........ we can run all 3 showers and the floor indefinatly with no loss of hot water

we have but one complaint with ours...you cant cool it down for short periods when needed, example: have a bunch of folks over for a party you have to open windows to cool stuff down with all the body heat. This is due to the fact that you are heating the structure of the home and not just the air in it. This will vary from home to home based on insulation and your system. Ours is on a slab on the ground floor but run between joists on the second floor and works great. You just have to completely fill the void between joists with insulation to help force the heat up although it will naturally want to go that way anyhow.

Done correctly these are efficient systems especially when powered with gas or propane as electricity is the worst for making heat. Our system is propane powered and yes it uses some electricity but minimal to run things and on our 2600 sq ft home we will use somewhere close to $100 worth of propane a month in the colder months. Home was built in 2000 with efficiency in mind but gives you an idea of what can be done

i like carpet and since the ground floor is a slab i wanted excellent padding, we used a thick and expensive pad which has not caused any problems with the function of the system. Have not noticed hot / cold spots in the upstairs joist install as once the sysytem heats all that mass it maintains it across the whole surface...id say if joist areas are hot/cold someone did not insulate between and underneath joists to spread and maintain even distribution of heat

we dont have any wood floors so id check to be sure but since you are only heating the floor and not adding or subtracting any moisture it should be fine???

contact me if you would like more info

Better systems go on top of the sub floor,
But you’ll probably need to replace most of your flooring to tile and wood,
Not so good with carpet, but it can be done.
Dedicated water heater/ boiler for heating is best, does not take much with a recirculating system, if you have room for it.
Zone controls and thermostats in every room are essential.

That's not something that can be retrofitted effectively

I've framed enough houses from scratch that had problems with it to know. All of those systems went above the subfloor

Trying to retrofit from below is insane. You'll heat more of you crawlspace or basement than the living space

It can be done, but not as efficiently as a new install.

My brother has what appears to be a retrofitted system in his house, utilizing two 40-gallon natural gas domestic water heaters. Seems to work OK for the two zones he has, but I wouldn't recommend it. Much better to use a dedicated boiler for the heating side along with a traditional water heater OR a water storage tank, like a Bosch SST, or, if you need a single unit, get a combi-boiler. You can get combi-core water heaters, but I've heard they don't get hot enough to burn off the condensate, so, according to the heating guys that come through, they rust out fairly often. Condensing boilers drain off the condensate, so they don't have that problem.

If you're going to use PEX tubing for your heating lines, make sure to get barrier tubing. PEX-A (cold expansion) and PEX-B (crimp) will slowly absorb oxygen through the walls of the tubing and rust out any steel or cast iron parts in a closed-loop heating system. PEX-C is designed for use in heating systems, and doesn't have that problem.