Under floor hydronic heat versus Radiators

[BigguyZ]

My brother's house was badly damaged in the Mpls tornado, and after a couple of weekend's worth of vigorous work at the house, the entire house is now gutted.

Unfortunately, even though it has a roof on it now, it took about 7 weeks for that to happen and there was a LOT of water getting in that needs to be dried out.

So now we're planning the major mechanicals for the house (electrical, plumbing, HVAC). It's an old house, so it has a huge boiler and radiators. The boiler is definitely being replaced, as are the steel pipe lines to the radiator locations (the pipes have all been taken out).

But my brother's wondering about the possibility of using underfloor heating for the first and second floors, rather than re-using the radiators.

Has anyone used underfloor hydronic heating? Menards has the Nibco "Rad Trax" plates on sale for $4.50 each, as well as the oxygen barrier pex that'd be needed. But my concern is that the system won't work as well. In theory, it sounds great, but you're talking about transfering the heat from the plank subfloor to the wood floors, into the room. Wood's not a great conductor, so how well would that system work?

Anyone use underfloor heating, or can compare rads vs underfloor?

Thanks,
Travis

[twistsol]

We put in underfloor heating a couple of years ago and love it. We used a retrofit system from www.Radiantec.com. The tubing is stapled under the sub floor from below and covered with aluminum plates to distribut heat. Our subfloor is 1/2 inch plywood under 5/8 particle board. We have either carpet or hardwood over that.

It cut our heating bill over 50% but there was some additional insulation added in spots as well

The one thing to know about it is that it heats up the mass of the floor before it heats the room. An automatic thermostat is pretty much out of the question. It takes about twelve hours for a change in the thermostat to take affect.

[atgcpaul]

My BIL has radiant on both floors of his house. Upstairs is carpet. Downstairs
is tile. Walking barefoot on the tile is great on cold days. I like to sleep in a
cold room so I wasn't too thrilled with the upstairs because my sister likes to
keep the house warm. Warm bathroom tiles are nice, though.

Almost every house done on This Old House is upgraded with radiant. I would
definitely do the same if I had the chance.

[BigguyZ]

We put in underfloor heating a couple of years ago and love it. We used a retrofit system from www.Radiantec.com. The tubing is stapled under the sub floor from below and covered with aluminum plates to distribut heat. Our subfloor is 1/2 inch plywood under 5/8 particle board. We have either carpet or hardwood over that.

It cut our heating bill over 50% but there was some additional insulation added in spots as well

The one thing to know about it is that it heats up the mass of the floor before it heats the room. An automatic thermostat is pretty much out of the question. It takes about twelve hours for a change in the thermostat to take affect.

What size tubing did you use?

[herb fellows]

Only second hand knowledge, but a friend had this and loved it, with one exception; it took forever to warm up if you turned it down.
I do stress however, with that exception, he loved it.

[twistsol]

We used the 5/8 tubing throughout the house under the floors and 3/4 or 1 inch copper to run the branch from the zone pump in the utility room to the start and return from each heat zone.

The exception Herb mentioned is a big issue. We made the mistake of turning the heat down to 45 while we were away on vacation and it took nearly two days to get the house back up to temperature.

One added benefit that we didn't anticipate. My teenage girls were in the habit of throwing clothes all over the floor of their rooms. When the floor was completely covered, that meant not as much heat and their rooms were cold. Clean rooms = warm rooms.

[BigguyZ]

We used the 5/8 tubing throughout the house under the floors and 3/4 or 1 inch copper to run the branch from the zone pump in the utility room to the start and return from each heat zone.

The exception Herb mentioned is a big issue. We made the mistake of turning the heat down to 45 while we were away on vacation and it took nearly two days to get the house back up to temperature.

One added benefit that we didn't anticipate. My teenage girls were in the habit of throwing clothes all over the floor of their rooms. When the floor was completely covered, that meant not as much heat and their rooms were cold. Clean rooms = warm rooms.

My brother is typically in the habit of turning down the heat to rather low when he's not home, so I'm wondering if the startup time will be an issue. Then again, with the additional insulation he's going to be adding (spray foam, versus the old insulation: nothing), it still may be more efficient... Also, I would think he'd have at least 2 zones, so he can keep the lower floor colder, while keeping upstairs warmer.

So what did you use for the heat source? An old boiler, a new boiler, your old water heater, or their water heater? I actually really like the idea of the super efficient water heater and using that for both the water supply and the heating. When you think of it, why have two heating sources trying to keep two tanks/ resiviors warm? Did you use a closed system, an indirect system, or the open system?

Thanks!

[twistsol]

We used their new water heater, the Polaris 50 gallon. Even with three teenage girls in the house we've never run out of hot water. When we installed it, filled it and cranked it up, the plumbers (I had pros do the gas line) thought something was wrong because it shut off after about 5 minutes. The water was already hot.

We used to have the electronic thermostat that turned the head up and down on a schedule, now all four zones are just set at 72 degrees 24/7. It worried me a bit at first, but we went from an average of 950 gallons of LP a year to 733 while replacing the electric water heater with this gas one.

The total investment was around $13,000.

[BigguyZ]

How long ago was that? I've seen that the SS tank had issues, but they moved to a new plant around 2007. But consistently the negatives listed are ignitor issues. Have you had it break down? If so, how quickly was it able to be fixed (and by whom)? How costly was that?

Also, is that an indirect or an open system? Just curious on that too.

I get really excited about the idea of this... but it's definitely a new idea.

I found the polaris for $500 cheaper than on the Radiantec site, or there's one by AO smith that's also 96% efficient, only 100,000 btu, and only about $2k shipped. So that's a $1k savings right there. BUT- it's a glass-lined tank. 6 year warranty, I think. It has an anode, which needs replacing every 3 years as well. But I haven't seen any complaints about reliability....

Sorry to pick your brain like this, but I'm trying to get as much info as I can- and as a fellow Minnesota resident, your experience is good to note.

Thanks!

[twistsol]

We installed it in November/December 2009 and haven't had a single issue with the heater so far. Radiantec included a spare igniter with it and it is sitting on the shelf waiting to be installed should it ever be necessary. I checked before I bought it an there was a company on the north side of Minneapolis that did repairs that said the trek down to Cannon Falls for a $50 travel fee in addition to their usual rates. I dont' remember who it was though. I find bad reviews online for all kinds of things and I wonder what the failure rate really is. You can have 20 disgruntled people posting everywhere they can and thousands of people who've had no problem never say a word. That worried me a bit as well, and I still think about it since I was never able to locate actual failure rates.

We installed it as an open system. It took some noodling to get the layout right with the check valves etc and splitting the incoming so I had unsoftened water going to some cold pipes in the house and softened to others as well as the mixing valve and running unmixed hot to the dishwasher.

Really, any water heater with appropriate BTU's should work. When I was planning this, the plumbing and heating guy who did our A/C recommended an off peak electric boiler and just use the gas water heater during peak electric demand. We get some pretty good discounts from the co-op for electricity on the peak cutoff meters so it would have been cheaper than LP in the long run but would have meant a water heater and a boiler in a room that's just plain too small.