Hydronic Radiant Floors - HELP

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Old 02-18-13, 07:51 PM
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Hydronic Radiant Floors - HELP

Hello! I am new to this forum so please forgive me if I am posting in the wrong place.

My husband and I just bought a house and have decided to redo just about everything. The house was built in 1921. The bathroom is pretty small - 5x10 ish. Because of this I would like to get rid of the radiator and install a heated floor to ensure we can put in a big enough vanity for a growing family. I have done some research and it seems like hydronic floors are most energy efficient way to go. WHile the DIY electric mats look the simplest, it also looks like they will cost the most in the long run. So my two questions -
1. are the mats as inefficient as other sites have said?
2. Our house is currently heated by a steam boiler and there is no real reason to change that at the moment. Will the hydronic system work with a steam boiler? Is it just as simple as installing a relief valve somewhere?

Any help/advice would be much appreciated!!
 
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Old 02-18-13, 10:31 PM
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Number one.... there's no such thing as an efficient or inefficient electric heat source. By the laws of physics, a given amount of electric power outputs out a certain amount of heat. There is no negligible variation.

Furthermore, electric heat is technically the most efficient because it it generated at the source; there are no piping runs or ducts were heat losses can occur.

The only way electric will cost more in the long run is if you pay more per unit energy output than gas or whatever specific fuel your steam boiler uses.


Number two, hydronic systems cannot be steam. They either circulate plain water or they contain a mix of water, anti-freeze and other chemicals.

The key difference between the two radiating components is that the underfloor tubing is one long, continuous piece (or pieces, depending on zones), whereas a radiator is a series of linked chambers.
 
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Old 02-19-13, 05:57 AM
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Hi LaBuckley and welcome to the forum.
Major renovations are a great opportunity to plan all of the improvements so they fit together nicely when completed.

I'm not a HVAC pro, but I can ask some questions to help determine what would be best.
What is under that bathroom floor. If it is a heated space, then the floor will have much of the heat you needs from the start. If it is over an unheated crawl space or cold basement, then perhaps addressing improvements down there would be a first step.

Placing the heat at the floor does help to keep the toes warm, but the amount of heat needed will be dictated more by the windows, walls, and heat loss from that room.

Venting will be necessary, a good quiet bath fan to remove excess moisture. As you air seal the house, excess moisture will become a problem.

If you truly have steam, I don't think it works directly with a in floor heat. Typically they reduce the temperature going to a floor to keep from cooking those toes. A standard boiler can have a lower temperature loop added, but I'm not sure about steam.

What type of flooring do you plan on? Will you be removing walls and ceiling at the same time?

That will get this process started, if we don't get the pro's attention we can have one move this to another area.

Again, welcome.
Bud
 
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Old 02-19-13, 07:58 AM
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Floor heat is HOT WATER... there IS hot water in a steam boiler.

It IS possible to run a hot water heating loop off of a steam system, but it is CRITICAL the piping is done 100% correctly. If this is a 2nd floor bathroom, I would give up the idea of running a hot water loop right away. You MIGHT be able to get it to work, but it may not work reliably in the long run. A hot water loop on the 1st floor above a steam boiler in the basement is do-able. You probably will have a heckuva time finding someone who knows how to do this properly.

If it's only the bath that you are looking to heat the floor, I highly doubt if you would consider it cost effective to do so.

Electricity is more or less 100% efficient. This doesn't mean it won't cost more to run it though... depends on how warm you want to keep the bath.

Insulation UNDER the floor would seem to be CRITICAL to economic operation.

I would consider the electric mat... make sure that it will meet the HEAT LOSS of the room in terms of BTU output.

Also look into a bathroom vent fan that is combined with a heater... that would only need to be turned on to supplement when needed. Wire a timer on the wall that automatically turns it off after a period of time.
 
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Old 02-19-13, 09:39 AM
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Our second bath has an electric in the wall heater with a fan. It's rarely turned on, and when it is it's super effective, quick and provides a comfortable warmth. And for sure, cost effective.

Operational cost is 20 cents per hour, if it's on continuously - but it cycles with it's own thermostat. It might be on for 30 minutes a day, if that, so... maybe 10 cents a day when it calls for heat. For $3 month, it's fine.

There are also overhead infrared bulbs in multipurpose (fan/vent/heat) fixtures for instant warmth.
 
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Old 02-19-13, 10:41 AM
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You could install a hot-water heated floor in the bathroom no matter what the height difference was from the boiler BUT it would be quite expensive. There is also the probability that you do not have enough floor area to use a radiant floor by itself to heat that room.

I think that TBurr's suggestion of an in-wall electric heater is a good one. The major drawback to it is placement, if you don't have the free wall space for the heater then it can't be done. A combination of a ceiling mount electric heater and an electric mat for the floor would probably work well.
 
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Old 02-19-13, 10:53 AM
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Thank you all for the input.

It is a second floor bathroom, right now the only bathroom in the house. (we plan to install a first floor half bath)
My husband is a refrigeration mechanic and was concerned that he could get it to work but not for as long as the floor would last! NJTrooper
We unfortunately do not have room for a wall heater. So I think we'll go with the mat and just be super conscience about it.
 
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Old 02-19-13, 01:28 PM
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Originally Posted by NJ Trooper View Post
It IS possible to run a hot water heating loop off of a steam system, but it is CRITICAL the piping is done 100% correctly.
Thanks... I thought it was possible but did not know if it was code and I have never heard of it being done.

As such, it seems something one would not want to pursue.
 

Last edited by Nick D.; 02-19-13 at 01:45 PM.
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Old 02-19-13, 01:44 PM
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For such a small room, I wonder if you could use the DHW system ?
Just a 'poor mans' system.. a loop off the water heater with a t-stat (or timer?) controlled circ pump ?
(providing your water heater has enough btu to warm the floor AND supply your shower/bath needs without running out of heat)
 
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Old 02-19-13, 02:34 PM
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It's really not that DIFFICULT to do, but as I mentioned, it must be done 'by the book'.

This 'handout' from Bell & Gossett explains how...

How to Run a Hot Water Zone Off a Steam Boiler | Xylem - Residential and Commercial Water Systems

In the case of a radiant floor however, there is more piping involved because you can't feed the floor heat with 180-200 degree water. One must also include a MIXING VALVE to temper the water going to the floor down to about 120 or so, and this setup would also require a second pump.

One more thing to consider... while a cast iron pump will work OK for a few years, the fact that steam systems are open means that there is oxygen in the water, unlike a pressurized hot water system, and this oxygen will eventually corrode a cast iron pump. BRONZE is strongly recommended... and they are pricey!

Furd stated that height didn't really matter... but [edit added in response to Furd's post #11, below] if one is running a hot water loop directly off the water in the boiler without an intervening heat exchanger and a completely separate pressurized system on the other side of the heat exchanger, it DOES matter.

A quote from the B&G article:

...but that zone must be not more than 30 feet above the boiler water line. At higher altitudes, it will have to be even closer to the boiler, because of the drop in atmospheric pressure.
Since steam systems are 'open', i.e. not pressurized, the only thing holding that water up in the piping is a combination of atmospheric pressure and the 'suction' (think of a finger on top of a drinking straw here) that is created by the gravity trying to pull the water back down into the boiler.

The higher you try to go, the more difficult it is to keep the water up in the piping.

This is the reason I wouldn't recommend it for a 2nd floor... it's not that it couldn't be done, just that I personally would not recommend trying.
 

Last edited by NJT; 02-19-13 at 07:42 PM.
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Old 02-19-13, 03:33 PM
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Furd stated that height didn't really matter... but it does.
No, that is NOT what I stated. My exact statement was:
You could install a hot-water heated floor in the bathroom no matter what the height difference was from the boiler BUT it would be quite expensive.
You would not use water from the lower part of the boiler direct but instead use an intervening heat exchanger. Pipe the boiler water through one side of the heat exchanger using a bronze or stainless steel pump and then have a conventional hot water loop on the other side of the heat exchanger complete with circulating pump, temperature regulating valve, air elimination device, make-up water system and expansion tank. The pump on the boiler side would be thermostatically controlled to maintain the proper temperature on the water side within a reasonable range and the temperature regulating valve on the water side would be used for final temperature control to the floor piping.

If instead of a residential steam boiler (virtually no pressure) you had a supply of steam at five psi or above you could use a steam-to-hot water heat exchanger and eliminate the SS pump. Somewhat different controls as well. Regardless, it would be an expensive system for just a bit of radiant floor heat in a small bathroom.

I've been in this steam business a long time. Next time you have a question just ask rather than trying to say I'm wrong.
 
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Old 02-19-13, 07:35 PM
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Sorry Furd, no disrespect intended... you know I value your input... BUT, without the further explanation you made in your last post about running a heat exchanger, etc., what you said in your first post DID say that height doesn't matter.

Just a misunderstanding is all it is... no anger needed.

I've added a few more words to my post that should help to clarify MY meaning.
 
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Old 02-20-13, 05:22 PM
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I think we'll go with the mat and just be super conscience about it.
If you're considering the electric mats then I'll guess that you're laying a tile floor. Correct?

One of the challenges with electric radiant floor heat is that the heat source cannot be installed under anything but open floor. That means that it has to be kept clear of the tub, shower, toilet and vanity. That can become very tricky when trying to use the mats.

When I re-did the second floor bathroom in our old house, my tile man and I laid heating wire between two layers of concrete base about 1-1/2" below the surface. The cable has to be installed as the full length - it cannot be cut - and it can't cross itself, but it is far easier to fit in than the mats are, especially if you'd like to curve it around the toilet, say.

If you draw your bathroom to scale, a heating supply store can tell you how to calculate the length you'll need. To adjust the length to the space, you can play with the spacing between the parallel loops. The one we used specified 3" spacing, but we calculated, purchased and installed it using 4" spacing. We installed a second cable on 4" spacing, offset from the first one by 2". In the thermostat box, we capped off and labeled one of the loops as a spare, to be used if the first one ever fails, and wired up the other one.

Most comfortable bathroom floor I've ever stood on, period, and the room stayed nicely warm too.

The whole installation took maybe a couple of hours, including both cables.
 
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