Details Hot Water Under Floor Heating??

[NY_Yankees_Fan]

I am about to start a kitchen remodel project and want to install hot water underfloor heating in the kitchen, about 18' long by 14' wide. Not sure how to go about it. I know from watching This Old House I can place the pipes with reflectors under the floor via the full height basement. Not sure but I think the water can only be a max of 120F or so. Boiler runs at about 180-220F depending on the outside temperature. So how do you control the temperature, a mixing valve? I assume a separate zone off the boiler, and PEX would work. Just not sure of the details. Do you think this is a do it yourself project? The flooring will be tile.

Thanks for your help.

 

[kubotabilly]

Tom,
Here's the infloor heat that I had used in the past and it works great Vanguard Piping Systems, Inc. - Welcome You do need a mixing valve to temper the infloor heat and yes it is a do-it-yourself project providing you can make the tap into your existing boiler. You may need a plumber for that end of it.

Bill

 

[DWW68]

A mixing valve and another pump for will be needed. That size room you will want to put in multiple loops connecting to a header. It can be a little costly, but the comfort of in floor heating is worth every penny.

 

[Asymtave]

Not sure if this is to code where you live but this was recommended to me by an old pipefitter I used to work with. He did in a house that he built:

I simply ran fin tube between the floor joists. They are not in contact with anything (except the steel hangers), but are closer to the floor above than the ceiling below (second story bathroom.) I laid fiberglass insulation in the bays with the foil side facing up to reflect the heat up towards the floor I was trying to heat.

The floor is tile and I always put a 3/4" mortar bed underneath my floor tile. So with the thermal mass of the mud and tile, the floor has a nice even warmth. Works awesome!

From my research into wood burning for heat, I understand that pyrolisis (sp?) of wood can't start until at least 180 degrees F. This is the only way that hot water heat can be safe in the first place, as pipes are going to touch the framing somewhere. So I'm not the least bit concerned about safety. I really don't see a downside. Dirt cheap and easy.

 

[quicksandfarmer]

I've done a couple radiant floor heat installations, and it takes a fair bit of design. In a conventional hot-water heat installation, you figure out the heat requirements for a room, then you order an appropriately sized radiator. With radiant floor heat, the floor is the radiator, and you have to design and build it on site. I would recommend an engineered solution, where you buy pieces of subfloor that are machined to accept tubing, which cuts out a lot of the calculations.

Just to give you an idea, here is a rough outline of the calculations in a site-built system.

First you do a heat loss calculation for the room. You can then calculate the heat output of a radiant floor. In addition to being a radiator, the floor is still a floor, and people need to walk on it. The recommendation is that no spot on the floor exceed 85F, so that bare feet are not uncomfortable -- (although I've gone as high as 100F with no complaints. ) So you calculate the output of a radiator at 85F with the surface area of the floor. It's entirely possible that the floor will not have enough heating capacity for the room, in which case you will have to add conventional radiators as well.

From the required heat output, you can calculate the required gallons per minute of hot water, and linear feet of tubing, and size your tubing and circulator appropriately.

Then you design the floor. You want to design your floor so that the temperature is as even as possible. A warm floor is no good if it has cold spots. Also, a radiator at 85F doesn't put out a whole lot of heat; you want as much of the floor to be as close to 85F as possible to meet your heating needs. The key to having the floor heat even is to have a uniform layer of a material with high thermal conductivity under the floor. Usually this is either poured concrete or aluminum plates but I suppose there are lots of things you could use. Even a lot of people in the business don't get this point; they talk about "thermal mass" but what you really need is thermal conductivity.

Above your conductive layer you can have a layer that is somewhat insulating, like wood or carpet -- you can just increase the water temperature until the surface temperature hits 85F. Since you want to heat your occupied space and not the space below the floor, you want to have insulation below your pipes, and the more insulation above, the more below. Also, all of the materials used have to be able to stand up to the temperature of the water.

Once the floor is designed the next step is the water temperature. Most likely the boiler water that is available is too hot and has to be tempered. You can estimate this as part of your design, but you'll want to have an adjustable tempering valve to fine-tune the floor temperature once it's up and running.

 

[NY_Yankees_Fan]

The room has no heat, but after 20 years of living in the house this has never been a problem because of the open design of the home. The sole purpose for the heat is to keep the better half from having cold feet with a tile floor. I want tile since I think a wood floor will not hold up, i.e. water from everyday use and a dish washer that has overflowed for one reason or another for the past 20 years. I have looked at an electric mat that is laid down and then mud applied over the mat and will heat the floor. But the cost of material alone was $2500 plus install. I think the electric will be more expensive to run in the long run, and will not last.

I like the idea of Asymtave of just running fin tube between the floor joists. My concern during cold months the water temperature is higher then 180F, more like 200F that can make the floor too hot to walk on.

More thinking and figuring on this problem.

 

[Sigarms]

Just remember, flow rate and water temperature.

Lot of guys use water heaters down here in N.C for room infloor radiant heat, but at the same time, have had to bail a couple out because they undersized the load for various reasons and couldn't get the water temp as high as they needed.

Makes for a very unhappy homeowner.

 

[Asymtave]

I'm not a heat flow guy but here's my take on it.

Since the fin tube doesn't actually touch anything, all it's doing is heating the air between the floor joists. Since I have an old drafty farmhouse, I put Blue Board blocking at either end of the bay and caulked them to prevent air from moving through. So the air in the bays reaches some equilibrium - I don't know what. This then transfers heat to the floor above.

So from my single experience all I have to say is that the floor is nice and toasty stepping out of the shower. Not hot at all just really nice. I think I had about a total of 20 feet of residential 3/4" fin tube in a 10 X 11 bathroom. My boiler is set and forget (for me literally!) so I think I leave it at 180F all winter. This circuit has a flow control (ball valve) in it to regulate the flow and allow adjustment separate from the rest of the zone.

And yes I misspoke earlier when I said "thermal mass." The themal conductivity of the mud/tile combo helps the heat from the joist bay go "up" into the room just as the insulation below the fin tube resists the heat from going "down" to the ceiling below. The thermal mass of my tile system evens out the heat between boiler cycles. I have never taken a pyrometer or IR thermometer and looked at temperature gradient across the floor, because it's not worth my time because my feet are happy!

Hope this helps.

 

[SpringHollow]

I ran my own in floor heat in my first floor when I renovated my house. It is very easy if you are installing it where there is easy access from below (ex., basement) and you are comfortable doing plumbing. If you like, you can even purchase pre-assembled manifolds. You can buy mixing valves that allow for different temperatures in your in-floor heat versus radiators. The manufacturer will design the tubing lengths and spacings for you. In my case, they thought might need the aluminum plates to help distribute heat. I decided not to use them because I could install them later if necessary. It's been about 15 years and I still have not needed them.

In-floor heat is extremely comfortable.

 

[ktm250rider]

I have radiant heating just too keep my tile warm in my kitchen and bathrooms. Also, in my garage but i did not use it this year. Check out these companies for information on DIY systems. Radiantec.com and radiantcompany.com. They can help you with all your needs. My system uses aluminum pex tubing nailed to the floor joists. I may try to increase efficiancy and use some al plates over the tubing.
My boiler runs at 190F. The water in my system never got over 160F. I have a metering valve that controls the mix of water from the boiler and return water from the heating lines. I can regulate the water temp with this. Room temperature was held at 66-68. I didnt need to heat the room to anything comfortable, just enough to keep the tile warm.
I would also suggest that you use a setpoing thermostat. It uses a remote sensor that gets installed into the floor. With it, you control the temperature of the floor rather than the room.
Oh yeah, i cant believe that i just offered help to a Yankees fan

GO REDSOX!!!