need radiant heat help

19 years ago

So, even though I am super busy trying to beat winter and get a roof up, I know I have ot be ready to get my heating system in place soon.

We are planning on using underfloor radiant heat with Al plates. We want to use a Munchkin Contender Boiler (or something similar) and have indirect domestic hot water.

My engineer that did my energy Calcs came up with a minimum load total of 68,439 BTU per hour. Using Slantfin, I came up with 50,000 BTU's per hour.

We use a woodstove to provide much of our heat. It is rated at 60,000 btu's per hour. We would like to set (and leave) the radiant and a low temp (just comfortable) and then use the wood heat to bring the warmth to where we want it.

I have talked to a few companies and I have received many different answers. They range from using 1/2" pex with no plates to 7/8" pex with plates. Many also quoted me with tankless water heaters, even though I asked to be quoted with Mod/con boiler and indirect DHW.

I am uncertain if my heat load calcs are correct (the seem high). It is a two story house with the master bed and bath in the loft. It has a large vaulted dining and living room. It is 2025 sqft, basically a 28'x44' building with about 2/3rds of second floor a loft. We have a whole bunch of large windows. I am using R21 in the walls, R38 in the ceiling, and R19 in the floor. The second floor will not be heated and I want to use a single zone.

I guess I am looking for some direction. I will be doing the majority of the work by myself. What would you do in my position?

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Comments (6)

oruboris
18 years ago
In my area, most of the companies that sell PEX will do some load calculations for free.

So I think I'd pick a local supplier with good prices, and make an appointment for a sit down meeting, where I'd go over the 2 sets of numbers and look for an explanation of the difference.
pinktoes
18 years ago
I would take my question to one of the pro forums on the web. I know I'm not supposed to direct you away from this site, but we got help that way. There are a lot of pros out there, esp. in the northeast and into Canada, who know a LOT about it.

Including, they directed me to buy the Bible of hydronic heat: Modern Hydronic Heating, 2nd Ed. by Siegenthaler. He's apparently the go-to guy. We got a used copy. Finally decided it would be worth the $ and it is.

We're having someone experienced in hydronic heating do the load calcs and the system design. We have a GC on our new house. But we will have right of approval on the system design. To be able to intelligently critique his design, we figure we need a good general education ourselves.

I'd ask the pros about the calcs.

Here is a link that might be useful: modern hydronic heating, 2nd ed
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rabadger
18 years ago
What methods did they use? Proper Floor heating requires much more than just BTU requirements. Everything can change from room to room. Required loops, GPM, fluid temp, etc.
mikeyvon
Original Author
18 years ago
rabadger - some of the companies that gave me quotes did figure required loops and other stuff. I will have to get it out when I am at home and look it up. We are doing a single zone.

My problem is I have gotten different answers from different companies and need to figure out which way to go.
pinktoes
18 years ago
Diff. quotes with identical equipment?
mittenpawak
18 years ago
A good site to visit is radiantpanelassociation.org - you can click on the radnet online link from there. I also enjoyed reading the info at radiantdesigninstitute.com.

Just curious: what design temperature did you use for your heat loss calcs? In just a rough comparison of your house to ours, it does seem as if your calculated heat loss might be high. The heat loss calcs we did for our house 3 yrs ago came out to about 67,000 btu/hr at our design temp of -47F. We've been heating for two years now and, judging by duty cycles on the boiler during cold episodes below our design temp, our calcs were a bit higher than our actual heat loss has proven to be. Our system consists of an oil-fired boiler, a tekmar 260 controller and 10 zones (valve controlled, one pump), all thin-slab hydronic heating about 3,300 sq ft living space and 400 sq ft garage.