Radiant heat in a 100+ year old house in Minnesota

jerdavismn

We purchased our 1908 house in Minneapolis this summer, and as part of that purchase we discussed radiant heat as an option for heating the first floor of the home with our realtor/contractor. They've done that for a number of homes, and it worked great. For reference, the home has original hardwood through most of the first floor, with plywood and a pergo like product in the kitchen. We were assured that radiant would work fine, and with our eye on refinishing the hardwood and gaining back some floor space - we had the original radiators removed from the first floor.

The original boiler guy came in and removed the radiators and reran pex to lines going upstairs (we left the original radiators on the second floor). However we weren't happy with some of his work, and eventually our realtor/contractor brought in another company for an additional bid.

The second company wanted to push us towards doing toe-kick in the kitchen to help mitigate heat loss from using the back door (coming and going from the garage). This added confusion, as we were told all along "it would work great".

Interested in getting additional input, we sourced two more companies to come in and give estimates. Those estimates came in 2 to 3 times over our original bids, adding even more confusion.

Through this I'd looked at trying to do a DIY install, did some research and started learning about the installation methods, transfer plates etc. One major point between the first two companies and the more expensive bids? Transfer plates.

He says they are a "bunch of BS", an "upsell". The heat will radiate equally between the joists at 180 agrees if insulated below when pecs lines are stapled to the joists. The transfer plate lines are installed at the subfloor which will cause potential damage from plumbers, electricians, carpenters etc. Doing the transfer plates in a remodel is very difficult due to all of the additional mechanicals running through the floor system.

The first two boiler companies don't use them. They do staple up. With comments like "They're a bunch of BS", "an upsell", "The heat will radiate equally between the joists at 180 agrees if insulated below when pecs lines are stapled to the joists. The transfer plate lines are installed at the subfloor which will cause potential damage from plumbers, electricians, carpenters etc", "I never use them, I installed them 3-4 times and had to rip them out 3-4 times", "they're noisy" - etc.

Now it's coming on October. We're confused and don't know what to believe. We're closing out our construction loan and will be paying out of pocket to finish this work so we don't tack a ton more on our end-loan with rates rising.

At this point I'm just not sure what to do or believe. We would value any advice on installations in this climate. Are transfer plates required? What are the pros/cons? Do transfer plates justify the bid being twice as much as one where they're running bare pex? Is one solution better/worse for use under original hardwood flooring?

Alan (California Radiant) Forbes

Hey there @jerdavismn: The first step to learning is confusion. Don't fret.

Using bare PEX tubing in the joist bays is the cheap way to go as it's less work and for the most part, it works. But it will only work if you run the numbers, i.e. do the room-by-room heat loss calculations to make sure the tubing will provide enough heat on the coldest average day. With such an old house in MN, if they haven't made it tight as a drum insulation wise, I would question it.

Heat transfer plates will work given that you do the heat loss calculations. It also has the benefit of working at lower water temperatures which means greater efficiency if you have a condensing boiler. Please tell us what kind of boiler you have.

However, if you use a low water temperature method for downstairs and have high temperature radiators upstairs, you will have a two temperature system; more involved piping at the boiler. That's a plus for the bare PEX method. One temperature for the whole house.

My preference for joist heating is Ultra-Fin. Easier than plates to install and it works very well. You only have to run one line per bay instead of two for plates. We've been using it for about 10 years.

EdTheHeaterMan

As a rule (see: Welcome! Here are the website rules, as well as some tips for using this forum. above) we don't talk pricing. That said, without the square foot of the project, there is no reference to what those prices mean. But you should still edit those number out of your post.

I have installed staple up systems where the homeowner did most of the tubing work. In my own home I have used the transfer plates. I have also put tubing in without the plates. I can't say if there is any difference in the heat between the different projects. (two different homes).

What i will say is that you must insulate below the tubing in order to direct the heat up into the intended room. One of the DIY tubing jobs I was associated with, the home owner did not properly insulate the floor below the tubing. AKA the basement ceiling. For 5 years I returned to do maintenance on his oil burner and the basement was like a sauna. much too uncomfortable to work in and the rooms above never got enough heat.

As part of the divorce settlement, the customer needed to complete all the unfinished projects before he could give Her the house... This included the basement insulation. Now the rooms above are comfortable, the basement is much cooler. and He said the insulation DID make a difference. But what did I know about heating systems. The customer is always right!

hot_rod

The key is knowing that there is a limit to how much heat energy you can get from a comfortable radiant floor. Defined as btu/ sq foot.
So especially in an older home a heat load per room is critical without one you are flying blind 

There are some online calculators or have a radiant supplier or manufacturer complete this important first step

Even before starting the load calc find any area where you can reduce the load. Extra insulation, weatherstrip upgrade, spray foam sealing etc.

A blower door test will point out infiltration leakage, the biggest thief of heat from a building 

An infrared scan will show where insulation is weak.

Then crunch the heat load numbers.

jerdavismn

Thanks for the feedback thus far.

• I edited the original post to take out the bid prices, just citing that the new bids with transfer plates and a seemingly more modern approach are two to three times more expensive than the original bids.
• Our first floor is roughly 775 sqf
• Our existing boiler is a Burnham Series 2, model204HNSL-BEI2 dated 06/2002

hot_rod

A very WAG would be 25 btu or more per sq ft for older below average insulated homes.

775X 25= 19,375 fro the first floor

But really, you need to do an accurate load calc. My money tells me your current boiler is oversized

This has a tutorial to walk you through the steps.


https://slantfin.com/slantfin-heat-loss-calculator/

Alan (California Radiant) Forbes

I don't think anyone answered your question about the kickspace heater one of the contractors suggested. While they do their job if sized properly, they can be an annoyance. Hot air movement at your bare feet is uncomfortable and they add a fan noise when you want a quiet kitchen with your first cup of coffee.

Kitchens and bathrooms with all the cabinetry and fixtures often don't have enough floor space to provide enough heat to warm the room. If you have any wall space or an end cabinet somewhere, a towel warmer would be my choice. Heat the room and warm the towels! A thermostatic radiator valve would turn on the towel warmer only when the radiant couldn't keep up. Lots of control options.

Kitchen appliances will also throw off heat to warm the kitchen, but knowing how much is difficult to calculate and should not be used in heat loss calculations.

I know that you just got rid of your cast iron radiators and now have more floor space, but considering that you have some issues with PEX tubing in the floor, another option would be European-style, wall-mounted radiators. Additional boiler piping would be kept to a minimum, one temperature for all your radiators and very little PEX in your floor.

GroundUp

While the price may seem attractive, anybody who says transfer plates are "BS" or that they "needed to rip them out" is so full of S&$@, their eyes are brown. I'd write them off immediately or sooner- they are not the right people for the job. Kickspace heaters can be great for certain spaces, but they are LOUD. I put two in my own house years ago to mitigate the cold in those two rooms during really cold days (I'm also in MN), and didn't even make it a full winter before I pulled them back out and replaced with underfloor radiant. I did bare tube staple-up in one room with 170 degree water, and used transfer plates in the other with 120 degree water. Before the next winter, I also did away with the staple-up and converted to plates with 120 degree water. No noise, no trouble, just a warm house- and one of those rooms has carpet.

mrlarson

I live in North Dakota in a 100+ year home which I call the 5 chicken coups. The floor joists run N-S and E-W so my challenge to install staple up plates and in-floor tubing was going to be a pain in the rear. Beside the floor joist issue, I have a forced air gas furnace, A/C with duct work to fish through cold air joists and over duct and round pipe, along with all the wiring and plumbing.

The use of plates was not going to work well so I opted for tube talons and foil backed bubble wrap to staple up underneath the pex pipe. This gave me the heat transfer across the joist and also gave me a small bit of insulation value incased in the squashed duct work system between the joists. I had no problem covering all pipes when my piping had to switch joist directions from one coup to the next on the zone I was working with.

I have 4 zones on low temp pex in my 1120 sq ft floor area and it works great, even floor temps, with 6" spacing between the pipe runs. I also added two high temp fan assisted convectors to the 315 sq ft entry on a spilt level ground floor which I couldn't install the in-floor underneath. The furnace I added a high temp water coil just below my A/C a-coil on my furnace.

Now most will think I'm crazy, but I opted for 4 thermostats, and switching relays vs a fancy and expensive Taco or Tekmar control system on the boiler beside my furnace. I have a tempering valve for the in-floor heating zones on its own t-stat the main stat in winter, one for the high temp coil in my forced air furnace set 2-3 degrees below the in-floor for those cold front days, one t-stat for the furnace and A/C which is turned down to 65 for back up if I have a boiler fail and a line voltage t-stat for the entry convectors which controls the fans and the high temp zone valve for that zone. My furnace fan runs 24/7/365 for my UV and filtration efficiency.

The bubble wrap sure solved my problems and don't see why it wouldn't yours. Watch out for those nails sinking trough the floorboards, bend them over or cut them off.

Mike Larson Plumbing & Heating
Carrington, North Dakota

hot_rod

You have what I consider a staple up system, the bare tube against the subfloor. Output will be somewhat limited, maybe around 12- 15 btu/ sq. ft. depending on floor covering.
With your other heat emitters, sounds like it gets the job done.

Alan (California Radiant) Forbes

@hot_rod Is there any performance data for that second diagram that shows fiberglass vs. bubble foil?

hot_rod

The insulation topic is Robert Beans pet peeve. Scroll down to the bottom for a bubble foil opinion at this link. To me the R-value number is the key, the thickness, but the bubble foil folks have a different opinion

http://www.healthyheating.com/Radiant_heating_designs/insulating-underslabs.htm#.Y0BL9-zMI-Q

TAG

hot_rod said:

The insulation topic is Robert Beans pet peeve. Scroll down to the bottom for a bubble foil opinion at this link. To me the R-value number is the key, the thickness, but the bubble foil folks have a different opinion

http://www.healthyheating.com/Radiant_heating_designs/insulating-underslabs.htm#.Y0BL9-zMI-Q

It seems to be the go to product in my area for duct wrap ..

hot_rod

TAG said:

hot_rod said:

The insulation topic is Robert Beans pet peeve. Scroll down to the bottom for a bubble foil opinion at this link. To me the R-value number is the key, the thickness, but the bubble foil folks have a different opinion

http://www.healthyheating.com/Radiant_heating_designs/insulating-underslabs.htm#.Y0BL9-zMI-Q

It seems to be the go to product in my area for duct wrap ..

A bit better then bare sheet metal, probably some sound deadening, nicer to look at perhaps