WARNING -- Beware of Radiant heat in a cold climate (windows, heaters)

[RayinAK]

Originally Posted by brewsterK

We have a house in the Northeast built in 1931. Two years ago, we converted what was originally an attached garage into a family room, and we installed in-floor hydronic radiant heating in a slab for this 20x20 room. The project was supervised by an architect. The pex tubing was properly placed. The walls and slab are properly insulated.

In our cold climate, this system simply does not keep the room warm in the Winter. It works for the milder conditions of Spring and Fall, but it is simply inadequate when the weather is cold. Today, with the cold snap we are experiencing, the room temp stands at 58.

The problem is caused due to the following:

1. Temperatures vary here from the 40's during the day to the 20's at night, and the constant floor temperature simply doesn't respond to the changes. In other words, in the rest of our house where there are hot water radiators, the heat simply comes on and the radiators get hot in response to falling temperature. I understand the concept that our problem must be due to inadequate insulation, need for more pex, need to sue the contractor, etc., but the fact is that where the heat source is constant and where the temperature varies widely, there is always going to be a lag while the heat "catches up" unless you have a way to increase the heat on demand for a surge. A radiant system simply doesn't do this.

2. Our carpets and flooring are causing the problem. I haven't tried removing the furniture from the room to see what would happen, but I presume the problem would disappear if we took up the large area rug and rug pad that covers the wood floor. Even though heat simply rises, and even though with a properly insulated slab there is ultimately no where else for the heat to go but into the room, it must also be true that it is possible to "insulate" the slab to the point where there is insufficient heat transfer -- the heat simply remains in the slab the way a pizza stays warm on the delivery truck because it is in an insulated bag.

And this leads to my major conclusion about the radiant system we installed: it is not much of a heating system where you have to select furniture based upon it. There is something wrong when the heating contractor is "partnered" with a decorator.

If you Google radiant heating systems, you get a billion hits for people who install them. These web sites all provide the same basic (canned) information about how great they are. But upon careful inspection, the success stories center around people who live in milder climates such as the upper South.

It's not the radiant floor that responds to temperature changes. The thermostat responds to temperature changes, which in turn directs the zone valve on and off as needed. The boiler too, responds to signals from the thermostat. If the temperature of the water returning to the boiler is colder than the boiler's preset temperature, it comes on and heats the water as it circulates through the zone.

The insulation is placed under the slab to prevent loss of heat underneath. Placing a pad and rug on top of the slab traps heat in the slab. You don't want any insulation on top of the slab. Hopefully the installer set the slab with its own thermostat and zone (zone valve) independent from the rest of the house.

For example, my house has three bedrooms, a garage, and a playroom downstairs. The house has 4 zones for the boiler to heat, and 4 primary thermostats: zone 1 is the living room and kitchen areas upstairs, zone 2 is the bedrooms upstairs, zone 3 is the large room downstairs, and zone 4 is the garage. There are secondary thermostats that work with the primary thermostats in the bedrooms, which in turn allows for keeping the temperature in one room different than the rest if needed.

[Radiantec Guy]

It's unfortunate that the original poster (brewsterk) had such a poor experience because it really gives a black eye to the industry. Radiant will work in cold climates but one must have realistic expectations when installing under floor radiant heat in an older home.

The lower the energy efficiency of a space, the lower the chance a radiant heating system will provide all of the necessary heat. A heat loss calculation is the most important step when considering a radiant heating system. Even if the radiant system cannot provide all of the heat to a space it can still be a worthwhile project because it will add significant comfort and increase the overall energy efficiency of the heating systems. In these cases, the existing heating system would remain and become the supplement to the radiant system.

Without knowing more about the project my guess is that there were several problems. 1) The heat loss is greater than the amount of heat you can get out of the floor 2) This was probably a staple-up system and aluminum heat transfer plates were not used. Aluminum heat emission fins can greatly increase the heat output of a system. Plus, the less energy efficient the building is, the greater they will impact the system performance. You can read this post about the benefits of aluminum heat emission finds here: Study of Heat Transfer Plates - Radiantec 3) The water temperature is probably too low 4) An air t-stat was used instead of a floor control. While many radiant systems will work fine with an air t-stat, a floor control works better in building that is not energy efficient or will experience wide outdoor temperature changes.

Have questions about radiant heat? You can reach me at Home of Affordable High Efficiency Radiant Heating - Radiantec

[swilliamsny]

The biggest problem we have with ours is that we're in a location where our only options for powering the boiler are electric or propane. We're using electric right now, and it's incredibly expensive. Hoping to covert to solar hot water soon, as my husband isn't comfortable with propane.

[thecoalman]

Originally Posted by swilliamsny

The biggest problem we have with ours is that we're in a location where our only options for powering the boiler are electric or propane. We're using electric right now, and it's incredibly expensive. Hoping to covert to solar hot water soon, as my husband isn't comfortable with propane.

Look into a coal boiler... no I'm not kidding....

Anthracite Coal & Bituminous Coal Heating

[clutchrider]

We have radiant in our home 3k sqft open floorplan. The kitchen is through the floor and other areas baseboard. We keep our house at 68 in the winter and have no issues with the cold. Located in CT where we can go 40's to 20's or lower depending. Never had an issue and we love it more than our old home that was forced hot air. That house was significantly dryer and more stuffy feeling than this one.

The only update I had to make was that our open floor plan conflicted with the upstairs, as our thermostat for the bedrooms was located in the hallway where there were 1) no baseboards and 2) open to the downstairs. So the heat downstairs radiates up and the rooms would stay cooler. So I moved the thermostat to our master bedroom and it keeps the upstairs much more comfortable. We are planning an update on the master bath soon and I am going to be removing the two small baseboards along the wall to make room for a built-in makeup vanity but also to switch the tile floor out and install radiant flooring.

[Coldjensens]

We have radiant heat in our 181 year old 3900 s.f. home. The insulation is not great because the old part of the house is post and beam construction which is very hard/impossible to insulate properly.

We are in Michigan. It usually gets into the -10 or colder for a few weeks and stays below 30 for months. We have no problems for the most part. (THe floor in our bedroom gets cold when it is windy, but that is an insulation issue, not a heating issue).

It is marvelous. Radiant heat is superior to forced air in every way except one. The one issue is you cannot use a radiant heat system for AC. Otherwise is it more efficient, healthier, more comfortable, more pleasant.

One nice thing about radiant heat is you cannot block it. Unlike forced air registers, you do not need to keep furniture away from radiators, or rugs from over the top. It is perfectly fine to put coats, boots, towels or cats on top of radiators. Radiant heat works by heating up other objects (floors, walls, couches, rugs, etc.), not by heating up the air inside your house. Thus, more objects simply make more things for your radiators to heat up and help your house hold heat better if someone opens a door or whatever.

A radiant heat system can provide as much heat as you want. Just add more radiators or if practical, turn up the boiler output. If the OP is having a problem, it is either an installation problem or an insulation problem. As a concept, radiated heat is the best way to go, it is just more expensive to install, especially if you also have AC. There is a reason you find radiated heat in the best high end houses being build today.

I am not sure what the highest output level you can use for the boiler is. Ours is set at about 177. Sometimes it goes up into the 180s. By the time it gets to the radiators, it is considerably lower, the radiators will not burn you, but they do get a bit to warm for continuous bare skin contact.

Radiant heat is somewhat more efficient than forced air. There are studies on this you cna find on the internet. If people are reducing haeting costs by switching to forced ai, it is due to getting a more efficient furnace (which can be done by getting a more efficient boiler). Sorry, but the assertion that forced air improves efficiency is simply wrong as a matter of physics.

[sholomar]

Electric Heat is 100% efficient...there is literally no way to make any electric heat source more efficient (aside from a heat pump but that is not really a 100% electric source then.. it's earth source) and any claims to the contrary are marketing gimmicks... though a pure electric baseboard heat will be somewhat more efficient than a pure electric forced air furnace due to heat loss from the metal ducting radiating a small amount of heat.. a bit of heat will end up in your basement but my basement is finished anyways. It's much less expensive to use natural gas compared to electric, so any way you can get a system in place that runs on natural gas, all the better, regardless of whether it's forced air, hot water, or whatever. Fortunately I do have what I want.. forced air furnace and central AC.. the furnace is 96.3% efficient.

If radiant heat works for you, great. I loved the hot water baseboards my apartment had. I didnt have to pay the heat bill and could keep it at the temp I wanted day and night.

[AlaskaErik]

It's used in Alaska both in homes and for aircraft hangars. If yours is not keeping up with the outside temperature, something wasn't done right during installation.

[Coldjensens]

While electric heat may be 100% efficient from a technical/scientific point of view, it is inefficient from a cost to heat your home point of view. Simply put, it costs more to heat with electric because of the cost of electricity. So when you consider efficiency as heat per dollar, or simply how much is you monthly bill compared to gas, electric is a very inefficient way to heat your house.

I think that is what they meant. They were not talking about the physical properties of a heating element compared to a gas flame.

[cully]

All of this is fascinating. Around us are beautiful large newer homes with radiant heat and only tile floor.

Also, just a little further out are the heated floors...heated by wood burned in a stove in a shed a few yards from the house. A lot of work so early, I thought. Shoveling snow before daybreak to get to that shed to replenish wood. But, these are farmers and horse people who are already up early and used to hard work.