DIY Combi install for Panel radiators

Bubblehead773 · February 2023

Hello all. I am new to the site and looking to get some information as I plan a radiant heat install for the next winter season. I have a few of Dan's books in the mail, but I have been searching this site and haven't been able to find answers to my specific questions. A little background on the house. At the time of purchase my 1000 squarefoot single story home only had electric base board heat. The winters here in Wyoming are pretty brutal and I am looking at replacing our pellet stove with panel radiators in each room. I have my eye on a Rheem 180k BTU Combi boiler with a minimum input of 18k (100k MAX) BTU. The initial design I have sketched down is a 3 zone, two pipe (parallel) system with the 500 sq foot basement as zone 1, all living spaces as zone 2 (kitchen, bath, mudroom, living room) and the 2 bedrooms as zone 3. All of the piping would be O2 barrier PEX (3/4 mains and returns and 1/2 inch feeds to the radiators)
I have done heat loss calculations for each room and determined the max load on the coldest day here would be around 61k BTU. And I have access to the joist bays throughout the entirety of the house.
I would love to do radiant floors through out, but while I have access to all the joists via the basement or crawlspace there will be lots of interference removal, not to mention pulling all the nails and screws that were shot willie nillie through the subfloor and not into joists. Also as it stands there is no insulation anywhere in the floor and I am apprehensive about adding it since there is currently no moisture issues.

1)Does each zone need to be under the minimum firing rate for the boiler in order to ensure there is no short cycling?
2) If not would a DHW tank act as a sufficient dummy load if the answer to above is yes?
3) Do any of you guys run magnetic filters on your set ups and are they effective in a pex system with new age panel radiators or are these mostly for retrofits?
4) If Radiant flooring is the way to go by popular opinion, is it absolutely required to have insulation in all the joist bays to keep the heat from radiating down into the crawlspace?

Thanks for any help in advance!

hot_rod · February 2023

When you consider a combi the first question would be how much hot water do you want. If you know the lowest incoming water temperature you can use the combi charts to see what the units will provide.

It comes down to running multiple loads at once. All combi can handle a single shower load. SO if you can live within the restraints of the DHW productions, on to the heating loads.

1000 square feet of space with a 61,000 load sounds off. I’d guess a load of 1/2 that?

A mod con will lessen short cycles, but on mild days it will still cycle.

Tighten up the load calc and then look at the smallest zone/ cycle rate

franzsf · February 2023

Also in WY, and installed a combination of underfloor radiant and panel radiators for a ~700 ft2 house. It works well, but I'd say the panel radiators probably contribute more to heating the house than the underfloor, but the warm floors are a luxury. In the shoulder season I can operate with condensing return water temps, but on days like we've had the last couple of weeks that's not feasible. Definitely recommend getting John Siegenthaler's Modern Hydronic Heating textbook. Also Joist Trak heat transfer plates. Helps protect against nails and the pex just pops in.

KC_Jones · February 2023

franzsf said:
Also in WY, and installed a combination of underfloor radiant and panel radiators for a ~700 ft2 house. It works well, but I'd say the panel radiators probably contribute more to heating the house than the underfloor, but the warm floors are a luxury. In the shoulder season I can operate with condensing return water temps, but on days like we've had the last couple of weeks that's not feasible. Definitely recommend getting John Siegenthaler's Modern Hydronic Heating textbook. Also Joist Trak heat transfer plates. Helps protect against nails and the pex just pops in.

That statement in bold is dictated by how the emitters are sized. If one designs the system around low water temps then you should be able to condense all season.

I too question the heat loss number of 61k. I'll assume the 1000 sq ft doesn't count the basement, so adding that square footage in we get 40 btu/sq ft. Heat loss is done with a manual J not by square footage, but to give you an idea. My 100+ year old home with almost no insulation, original single pane windows is barely even getting to 40 btu/sq ft.

If the heat loss is indeed that high, I'd be looking at putting my money into envelope improvements long before I spent money on changing the heating system. It's a much better way to spend the money in the long run, after that I'd consider changing the system.

Why are you concerned about moisture with adding insulation in the joist bays? If you start having moisture issues with the insulation, the insulation isn't the problem, the reality is you already had moisture issues prior to insulating. But for radiant, the insulation is a requirement for it to work properly, otherwise you end up heating below, not above so much.

Bubblehead773 · February 2023

Thanks for all the insight Gents! Yeah I added a 15-20% fudge factor on the heat loss calculations. The house has no insulation in the exterior walls and the electric baseboards combined we around 45K but really struggle in the cold snaps. The house is a total of 1400 square feet including the basement (where surprise there is also no insulation) So that 60k includes two large loads in the basement finished areas. But I will definitely go ahead and pull the trigger on "Modern Hydronic Heating" The general consensus from this site is that it is worth every penny.

The main reason I worry about insulation is my Tennessee farm house was un insulated so I added bats to the entire crawl space area and within a year I was having moisture issues in all the cabinets. Probably less of an issue out here in the high desert.

DIY Combi install for Panel radiators

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