6 posts / 0 new
Last post
Radiant heat in old houses

I have a wood frame house in Cass, WV built in 1905. It was added onto in 1917 and a coal fired boiler, later changed to oil, was installed. The system used hot water with cast iron radiators and heavy black iron pipe.

The house has undergone extensive restoration, not renovation and three radiators were removed in the kitchen, bath, and entry hall.

Do to a major freeze up the entire heating system (boiler, piping and radiators) has to be replaced. We have learned our lesson and are installing a thermostat that will call us if the temperature drops below a set point. (We do not live in the house, it is a weekend getaway.) In addition the system will be piped with Pex and filled with anti-freeze.

What I want to ask you is the feasibility of installing radiant hot water heat in the floors in the kitchen, bath and entry hall. These floors are ¾” pine subflooring, black felt paper and 5/8” oak and maple flooring.

The local contractor states that it won’t work. He says the floors are too thick. I have checked old articles in Fine Homebuilding and TOH, and they don’t seem to see this as a problem.

Can you help?

Re: Radiant heat in old houses

I would get a 2nd and a 3rd opinion from other radiant floor heat installers.

Radiant installs are still new enough in the U.S. so that there is still a shortage of experienced installers in different parts of the country.

Consult the Yellow Pages in your area under "Heating Contractors"; the display ads will indicate which ones install radiant.

Your local library has Yellow Pages for all the large cities in your part of the country; while there, ask the reference librarian to see the Blue Book of local A/C & Heating Contractors.

Also consult the Yellow Pages under "Heating Equipment & Systems- Parts" in the largest city near you; phone them up and ASK TO SPEAK TO THE COUNTERMAN IN THE PARTS DEPT.

Ask the counterman to refer you to 3 highly experienced radiant floor installers in your area (they may ask you to call back after they check around); do this with several "heating equipment" shops until you get the referrals you need.

It's important to get 4 or 5 estimates, as the price quotes will vary widely.

The countermen deal with these contractors day in & day out & know who the best ones are.

If there is thick carpet on the floors in question, then I could see his argument, otherwise, this seems just the opposite to my experience.

To understand radiant, one must see the entire floor as the radiator (which acts much like the cast iron radiators you had before, but at a lower, more subtle temperature of ~100 degrees).

A floor this temperature hardly feels warm; yet, what has happened is that tens of thousands of btu's of heat have been pumped into the wood (this often takes hours to accomplish), and these heat btu's will spend the next several hours radiating their heat into the room.

That's why cast iron, wood and stone/concrete slabs are used in radiant; they can store a tremendous amount of heat in their bulk & release it over time.

If you remember your experience with the cast iron radiators, even after the circulator stopped pumping hot water into them, they remained hot/warm for hours, allowing the boiler to remain off & thus saving fuel.

This also assumes there is subfloor access to the flooring joists & there will be a sub-floor staple-up with aluminum shielding.

If there ARE any problems down the road with the kitchen & bathroom, once the radiant is installed, they can always be hooked up to a separate zone manifold with a slightly higher temp.(this is often needed for the bathroom in winter months).

From your post, I'm not sure how far along you are in the heat installation process; or if the present contractor has already been hired.

A radiant distribution system (piping) is often combined with a new gas-fired condensing boiler on a new install, since these are ~95% efficient & are tailor made for producing the 95 degrees hot water used by radiant.

But in your neck of the woods, A/C & a longer cooling season is usually much more important than heating; you would still have to install a separate A/C system if you install radiant heat.

If you have natural gas in your area, the latest gas-fired condensing forced hot air furnaces are also getting ~95% efficiency; this could be combined with a Unico A/C system or heat pump in one package.

Make sure you take care of insulating the exterior walls before any heating/A/C installs are done.

If you need any insulation, now is the time to do it; see "Insulation Contractors" in the Yellow Pages; they have a service where they remove a piece of siding here & there & blow in cellulose for a few hundred $$; this is extremely important in saving big $$$ on heating & cooling bills.

Once the insulation is installed, you can calculate the btu rating needed on your heating equipment & A/C equipment; the insulation will allow you to see a 25% drop in heating & cooling bills; the new heating system should drop bills another 25%.

If nothing has been installed yet, I would have you also consider the forced-air Unico system, if the house is going to be continued to be used only on weekends.

The Unico system snakes 3" diameter flex tubing thru the walls & under floors to supply forced hot air in the winter & A/C in the summer.

A forced air system will not freeze if the heat fails & is less expensive to install & maintain than a radiant system.

Although the radiant system will be filled with propylene glycol, this stuff costs $10-$15/gallon & what's removed has to be replaced every time service is done on the piping.
If there is still time, I would get an estimate for both the radiant floor system & the Unico system, compare the two estimates & then make a decision.

Although I live up North where we have much longer winters, & radiant is valued for superior performance, the payback ofen takes much longer, & radiant is inherently more complicated & expensive to install.

On the PMmag site enter "a little floor warming please" in their search box"; also enter ""radiant floor heat" in the PM site.

At the Wood Floor site, scroll down to click on "radiant & wood floors".


Re: Radiant heat in old houses

I do not see a problem with what you want to do. My friend did it in his new house in Vermont with 3/4 Avantech sheathing and 3/4 inch oak on top of that. It works great for him. I used the same thing on my house during my remodel and I have 3/4 inch plywood and an engineered wood floor. Last winter was my first winter with it and it worked great for me. You have pretty much the same thickness as me so you should have no problems. The key is to have the system sized to your house and insulation levels. Hope this helps you out.

Re: Radiant heat in old houses

From the above posts, it sounds like your floors thinckness may be OK. I have a similar question but my floors are even thicker: 2 layers of 3/4" plywood (needed to bring the level up to the previous owners addition), 1/2" cement board, grout, and 3/8" ceramic tile for a finished floor thickness of about 2.5 inches. I would like to install PEX and aluminum heat transfer plates in the open joists below in the basement but am worried about the poor conductivity of the 1.5" of plywood. Or is this not an issue if I use the Al transfer plates and insulate the joists when the install is complete?

Re: Radiant heat in old houses

I don't see any problem using radiant in this application.

The only big problems I've heard of is when someone tries to use thick, plush carpeting over the radiant floor.

It would help if you have a heat source that can vary the water temp from say, 90 degrees to 120 degrees to give you more leeway in controlling the floor temp.

Do you intend to attempt this yourself, or hire a contractor.

Re: Radiant heat in old houses

Thanks for the info. I would be doing this project myself. I've never messed around with radiant heat but my 1st-floor kitchen and bath shouldn't be very difficult. There is lots of of information online about plumbing and sizing boilers also.

Sponsored Stories

TV Listings

Find TV listings for This Old House and Ask This Old House in your area.