Radiant heat not cutting it!

Jason_Talbot

Hi--
Recently moved into a 4 floor single family victorian home. We converted from OIL heat to GAS (viessmann vitodens 200) and ripped out all the radiators. We now heat and cool the top 2 floors with HYDRO-AIR (spacepak). We have a spacepak unit running AC for the basement and first floor. To heat the FIRST floor, we tacked up RADIANT heat under the floor with uponor transfer panels and insulated the joist bays pretty tight. We lay a new concrete floor in the basement with embedded RADIANT.

Everything works OK until the outside temperature goes below 20F. Then we have trouble heating the FIRST floor (with the tacked up radiant). The first floor struggles to get to temperature (we usually keep it around 70F). This weekend it is below zero temps outside and first floor cannot get above 60F. It is running 24 hours a day and is not enough to heat our main floor. Basement radiant works fine (basement is much better insulated)

First floor loop is sending hot water at 140F and it returns at 130F.

Question--my contractor assured me the radiant would be sufficient to heat the first floor but clearly that is not the case. What can be done? Since we already have central air running to this zone, how hard would it be to add a heating coil to the hydro-air? Not sure how the thermostats would work in this scenario. Any other suggestions?? Really appreciate all your input.

Many thanks
Jason

Paul S_3

Is the staple up radiant insulated below it?....also staple up radiant only has the top part of the pipe in contact with the floor, the installer shouldve had a full loop of pipe in each bay with special fin connectors to increase the surface area of the radiant tubing....what i mean by full loop is there should be 2 pipes in contact with floor per bay plus insulation below it with about a 2 inch air gap with the foil side facing up....sometimes you do not have enough floor area to properly heat room during cold days....in that case i usually use a 2 stage tstat with perimeter baseboard or in your case a hydronic coil in an air handler.....where you located

jonny88

If insulated below tubing they recommend a 2 inch gap between tubing and insulation.

Jason_Talbot

Yes well insulated with a small gap between insulation and pex. Two pipes per bay attached to uponor steel transfer panels. Installation was done more or less correctly I think. Problem may be the subfloor and hardwood over it are just too thick and heat loss from first floor is too great.

If we added hydro air heat coil to our AHU how would we control it? And how easy is it to add the coil?
Thanks
Jason

Jason_Talbot

This is the AHU

hvacplumber7

He said he has uponor transfer plates, so I believe that the insulation sould be tight up against the tubing. What type of floor covering do you have. Carpet with thick pad or even double pad will defiantly affect how much heat you can get out. Also what type of windows do you have? How old is the house? Was a room by room heat load calc done by the installer? And what is your design temp in your area? Might just be that your water temp is too low for this temp.

hvacplumber7

If I remember correct. That small removable panel between the blower and the A-coil is where you slide in a hot water coil.

Jason_Talbot

Thanks. minimal carpeting. Mostly bare wood floor. Windows are all new replacement high efficiency double paned Marvin integrity. Walls have blown in insulation though it's not as tight as the basement that has foam sprayed insulation. House is from 1870s I don't think there was a heat calculation done. I had thought water temp of 140F was at the high end of normal.
Jason

gennady

Due to limitation of floor temperature radiant systems are not sufficient at extreme outdoor temperatures when house envelope is not tight and not well enough insulated. It requires auxiliary heat.

Harvey Ramer

What is the surface temperature of your floor? Check in a couple spots throughout the floor. A laser temp reader works good for that.

SWEI

You may need to increase the water temp at the low end of the ODR curve. Wait, let's back up a bit. Can you post a photo of the boiler and associated pump(s), valves, and piping? Is there an outdoor air temperature sensor installed?

Jason_Talbot

1 boiler w outside temp sensor
2 radiant manifold to first floor
4 piping to both radiant zones
5 boiler

SWEI

That manual thermostatic mixing valve is limiting the water temp supplied to the floor. In the short term, you can increase the setting on that valve a bit which will allow hotter water to be supplied to the RFH zone. It really should be replaced with a motorized valve that the Vitodens will manage.

GW

Ah yes, what temp are you setting your thermostats to on the upper 3 levels?

Jason_Talbot

Thanks. The mixing valve is always open full bore.

hot_rod

Looks like the mix valves are supplying about 110- 120°? What temperature is the boiler operating at? You may just need another 10 degrees or so to the radiant. Boosting the boiler supply may get you there.

The info should be in the design and load calc as to what supply temperature you actually need.

120 supply with a floor R-value of R2, 3/4 softwood 3/4 hardwood, should give you about 25- 26 BTU/sq. ft, based on the Radpad numbers.

Ironman

I looks like your installer takes pride in his work, but if he failed to do a heat loss calc, that was a fatal mistake. This is the main reason that radiant floors don't perform as intended and get a bad rap: improper design - or none at all. The heat loss calc is THE FOUNDATION for every aspect of design and engineering. Without it, you're simply living in fairytale land wishing that everything will turnout alright in the end. How can you hit a target if one doesn't exist?

You already have the two options on the table: either increase the supply water temp or add a hydronic coil to the SpacePak.

GW

3rd idea/opinion, get some heat going in the upper floors, stop asking the 1st floor to heat the whole house.

Jason_Talbot

GW- upper 2 floors which are heated with hydro-air are consistently set at 63F. Basement runs around 70F and is always toasty.

Hot rod- the temps you mention are for the basement. The first floor is sending hot water at 140F which returns around 130F.

Ironman--I hear you about the heat loss calc. Our outside design temp is 9F. I don't think anyone ran the numbers (I wasn't aware of the importance of this at the time). I think the boiler runs at 140F. Can the radiant safely be run hotter than 140F? Is there a quick and dirty way to do a heat loss calculation? The first floor has heated rooms above and below, is about 700 sq Ft and has 14 windows and 3 doors. Mostly tight with a few drafty spots in the kitchen where we didn't replace the 2 windows yet.

Also--if we did add the hydronic coil I'm not sure I understand how we would coordinate the radiant and the hydro-air together. Any thoughts?

Greatly appreciate all your insights
Jason

GW

Jason, humor me and crank up your second fl to 70, see if the 1st fl gets warmer. I am confident your issues will go away. The taller the house the more mamma nature want to take your heat and send it for a ride up the stairs.

njtommy

Controlling the hydroair/spacepak with radiant floor is very easy to do with a 2 stage heating t-stat. First stage would be Radaint heat and second stage would come on say at a 2 degree differential from set point. It's really not a bad idea to add to your system any way for a back up or larger thermostat set backs.

Snov001

From what I gathered, the problem zone is the staple up zone. He is pumping out 140 degree water and returning 130. The Delta t is a bit narrow. I see you have flow gauges on the manifold which is helpful. If you can find the heat loss / gain for the radiant side of this project it would be very helpful as you can see what the loop flow rate is required and adjust by checking your flow indicators. If not, check each loop delta T. Your figures of 140 and 130 can be deceiving if you are only checking manifold temp and not each loop temp. You could have a few loops with no Delta T giving you a false information. If you can't find the loss data try this. Check # 1 supply loop temperature and #1 return loop temperature. If you only have 8 degrees or so... slow the flow down until you get between 15 and 19 degree difference ( Delta T ). Set all loops up this way then go back to zone 1 and check again. The supply water temp may change but your delta T should not fluctuate that much.
Good Luck
Steve

Jason_Talbot

Thanks Tommy--i didn't realize there were two stage thermostats. that sounds perfect if we wind up needing the hydro air

Jason_Talbot

Steve- thank you so much for the detailed information. This strategy makes a lot of sense to me. I will see if I can measure the loop temps.
Jason

Ironman

I have to agree with Gary about setting the t'stats above to 70* to reduce any upward heat loss and natural convection.

It's probably not a good idea to raise your SWT above 140* if you have dimensional lumber. Do like Harvey suggested and shoot the floor surface with an infrared thermometer. If you give us the average surface temp, we can tell you how many btus per square foot the floor is emitting.

You can download a simple heat loss app from SlantFin.com and calculate what the actual heat loss is. By comparing that to the actual floor output, you can then determine what needs to be done.

Snov001, welcome to The Wall. I appreciate you insight about balancing the flow and checking the deltaT in each loop individually. Good advice with one caveat: slowing the flow to widen the delta T will not increase the floor's output. Btus = (gpm x 500) x delta T. We typically design our floors in living areas for a 10 - 12* delta T. That helps keep the floor temp consistent.

Mike Thomas_2

I would get someone into do a blower door test. That old house probably has lots of places that are losing heat. Tightening it up might make what you have work, and you will save money at the same time. Saving btu's is a lot easier and cheaper than making them.

Jason_Talbot

I'm reviving this thread as finally my contractor is attempting to fix the underperforming radiant on our main floor. His solution was to install a Viessmann automated 4 way mixing-motor valve that talks to the boiler. His explanation is that depending on the outdoor temperature, the valve will increase flow to maintain the heat. Unfortunately, thus far this has not fixed the problem and the floor still fails to achieve the desired temperature. In fact, it's worse than it was before he installed the new valve. We are heading into single digit weather tomorrow and I am scared what's going to happen.

Since he installed the new valve, he has been gradually increasing the heating curve up on the boiler but it doesn't seem to have made a huge difference.

I would like to try and at least understand the basics of how my Viessman Vitodens 200 is set up. In the "heating" menu I see two "heating circuits" (HC1 and HC2) each with their own heating curve. Yet, I have 3 heating "circuits" in my house (two separate floors of radiant each with their own manifold and mixing valve and one hydro-air circuit upstairs. When the contractor comes to adjust the heating curve for the main floor radiant, he adjusts HC2 and it is currently set at 1.6 (I am including a photo).

Can someone please explain how the heating circuits work on the boiler? Shouldn't there be 3 heating circuits?

Also what does the "room temperature" refer to? and does it matter that the outdoor temperature on the display screen is consistently 8 degrees warmer than the actual temperature outside?

Steamhead

Jason_Talbot said:

Hi--
We ..... ripped out all the radiators.

That was your first mistake, without which you would have plenty of heat.

Paul Pollets

HC2 controls the mixing valve. A curve of 1.6 is high for a radiant floor. Is it a staple-up installation without transfer plates?

Paul Pollets

After reading the above posts, I'd be using the air handler for supplemental heating. Pushing the heating curve hotter can result in warping the flooring if surface temps exceed 85 degrees. It's also expensive to run at high temps.

jumper

Floor radiant is nice when it is but when it doesn't suffice it's not. A service garage had floor radiant. Door opens & closes all day to let cars in and out. Theory was that thermal mass of slab overcomes cold air intrusions. Another intention was for mechanics standing under cars to enjoy heat from below. Well every time door opened blast of cold air was unwelcome. Installed unit heaters. Boiler and all that piping were for nothing.

ChrisJ

I agree with @GW .

You're running the upper floors chilly which is increasing the heatloss on the first floor. How do you get to the upper floors? Open stairwell? If so your heat is shooting right up that to the cooler floors like a chimney.

I also agree with @Steamhead but it's too late to change it.

schtoink44

@Jason_Talbot were you ever able to resolve this issue?