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New Garage Radiant Floor Heat system only getting air temp up to 55F
I have just finished installation of a slab on grade floor heat system for a garage / workshop (roughly 6" slab). We put in a closed system with 5 loops of 300 ft of 7/8" PEX tubing. The building is a steel building, 50' x 35' (WxL) 14' high on the sides and 22' high in the center. It is an unfinished concrete floor. This is my first floor heat system and so I worked with a supply/design company to help design the system and determine the boiler, feet of tubing, tubing diameter etc., but we did the installation, wiring and concrete work ourselves. We went with an electric boiler rated at 68k BTU. I filled the system with propylene glycol, but have struggled to find out what the exact mixture should be, as it has been extremely cold lately we have probably too high a glycol to water mixture. Our shop is in Virginia and we hope to keep it at around 65-70F so we can do fiberglass work year round.
Under our slab we have 2" green board insulation and a vapor barrier. We are in the process of insulating the building with a radiant barrier/reflective foil closed-cell polyethylene foam.
I have been running the system non stop for 3 days and the slab has come up from 34F to around 60-70F, but the air is still only 55. The inlet water temp is around 115-120F and the return water temp is around 80F. When I ordered the system I indicated the building dimensions and at that time we weren't planning on insulating the shop. The company recommend the 68k BTU electric boiler and the tube layout. At this point I am worried that we don't have enough BTUs to properly heat the shop. It is quite cold at the moment (15-20F at night and around 32F during the day. I am planning on thinning the glycol mix and making sure there is no air in the system again this weekend, but I am worried that the system just isn't enough for our shop. Any ideas or thoughts are greatly appreciated. We considered using tap water only, but with the recent temps we were worried that the slab was too cold. The boiler is a 240v, 80 amp unit. My concern is that it has been running non stop for 3 days and doesn't seem to have gotten the building up to our needed temp. In some areas (right by the manifold) the slab is quite warm, but further away it cools down to close to 50-55F.
I would appreciate any advice or thoughts on what we may have done wrong or can do to remedy this problem or at least get more efficiency from our system.