Radiant Floor Heating added in a 100-yr old house

[GB]

I'm in the process of getting quotes for hydronic radiant floor heating to be added to my 1st floor of my 100 yr. old house. I live in NH and the winters are cold and the woeful baseboards can not keep up. I'm thinking heated floors would be a great addition for comfort/convenience/efficiency/resale value.

My basement has full access and is cement floored. The floor joists are accessible but are not all on 16" centers. The centers range from 13" to

22"! Damn old home builders! Makes insulating a little more difficult but I'll manage. All of the exterior walls have blown-in insulation and all of the windows are double hung, thermopane windows.

My oil-boiler is less than 20 years old and seems to be working fine (87% efficiency according to last tune up).

Has anyone done this and regretted it? I'm sure it's expensive (probably between $5k and $10k) but I'm really wanting to try this.

I would put up Reflectix insulation to reflect the heat back into the floor. The latest technique seems to be hang the PEX tubing about 1" under the subfloor, attached to the joists. Then insulate the hell out of it (R19) to heat up the "pocket" of air between the joists and push it into the floor.

Then you set the thermostat to one temperature (68 or so) and leave it. None of the turn-down-at-night-turn-up-in-morning scenario. Set it and forget it.

I've been in a couple houses with this and I was instantly hooked! Warm furniture, warm feet, generally a comfortable and cozy feeling.

With winter in New England last about 6 months (!) I figure I need to upgrade to help be comfortable for half my life.

Thoughts/tips/tricks/caveats?

Thanks.

[yourname]

You will want to nail heat spreaders[ aluminum thingies] to the floor and then pop the tube into them. I would not think you would want suspended tube, very inefficient. If you are running it as a secondary system, you really need to put a primary secondary system to lower the water temp to the floor. Insulation below is of course a must.

go to heatinghelp.com 'the wall' and there are a lot of pros there who know quite a bit.

If your house is well insulated, it shouldn't take much to heat it, so I might look at what is going on there as well, not that radiant isn't great.

[Edwin Pawlowski]

Why does the baseboard not keep up? If the boiler is not putting out sufficient heat, the radiant heat will be no better. It takes a certain amount of Btu's to heat the house no matter what type of system you use.

Is the radiant heat going to run off the same boiler or an additional one? If the same, thee are water temperature considerations. Before you spend a lot of money, be sure you have the figures as to how much heat you need and be sure you have the ability to generate it.

[GB]

The baseboard is woefully under spec'd for the home. Original house has huge cast iron radiators. Previous owner decided to add baseboard by himself. He ripped out all the rads and mickey-moused a baseboard setup.

HVAC company came in and did a calculated heat load for my house and my system. There should be X amount of feet in each room and I'm anywhere from 5-12 feet short of baseboard in various rooms. The runs is not in a "loop" but each baseboard is tapped off the supply line and returned to the supply line with tees. Also...the baseboard supply lines are 1/2" from the boiler.

HVAC company wants to pull it all out, replace with 3/4" feeds and add baseboards in a bunch of rooms. He quoted around $2600 for this work. An additional quote was near that so I'm not too keen on that since the contractor said "That might do it".

If I'm going to pay that much, I'm gonna go the whole boat to a radiant heating system. More energy efficient, nicer heat, warm floors, etc.... High initial cost but that's OK. I can suck it up. I'm sure the benefits will be worth it in the end.

I've been in a couple of homes that have this retrofit and both had the tubes suspended in the joist bay, not stapled directly to the subfloor. Apparently, if you insulate well, it's not that much more inefficient than the aluminum plates stapled to the subfloor. I've heard from many that this methods is noisy as the plates expand/contract. If you ever add hardwood flooring, nails can penetrate the PEX tubing during install. Hanging them 1" down the joist helps alleviate this possible problem.

Plus, when I remodel a couple of the rooms next year, baseboards won't be in the way of new drywall/plaster and furniture can be pushed up against the wall...along with TVs and stereo equipment.

[yourname]

I think it is significantly worse, but I could be wrong

glue is the answer. The pex expands in the alum, but if it is rtv or urethaned in, it can't

If they are in plates, you know where they are. My above the subfloor system had no punctures.....til this year, under the floor where it exited, caught it before sheetrock went up, so same could happen in any system. If you ever add hardwood[is this really oging to happen?], you trace the[ perfectly straight] path of the tube in plates, and avoid them, usually running at a right angle to the tube helps.

[m Ransley]

An oil boiler 20 yrs old, 87%, how did they test it, because I dought it.

[GB]

It's on the spec sheet after they clean and service it.

87%. I thought that meant efficiency but maybe it means something else.

[Edwin Pawlowski]

I have the same thing and yes, efficiency. . Reads 87.5% one year, 88% another year, after cleaning. My heater is 28 years old.

[yourname]

That is a gross efficiency number, really a blind friggin guess, not an afue

[m Ransley]

They mean burner efficiency, not boiler efficiency. Testing a burner is fairly easy , testing efficiency of a boiler gets into alot of parameters and time. It is likely an 77-80 % unit overall at that age. You can have an 87% efficient flame and a 60% efficent boiler design ,for example. Non condensing wont be over apx 83%.

[andrew.alexander.burgess]

I wonder if you need to insulate that much. Still air is R5 per inch for downward heat flow so it would seem a radiant barrier would be enough, maybe with a small R-value since it won't be 100% reflective and will get warm. I was planning to try this with 1" polyisocyanurate board across the bottom of the joists and nothing in the joist bay except the pex.

There is also 'local wisdom' here that heat spreaders can be replaced by higher water temperature. It would seem that hot spots would be the only downside and your idea of hanging the pex would reduce that as the air at the top of the joist bay above the pex would get heated convectively, whereas the air beloww the pex would be stagnant and thus R5/inch.

HTH