Adding a supplementary heating source to radiant system

Jim46

I need to add a supplementary source to my radiant subfloor system. The temps on the water are running too high on cold days to keep the house warm. My contractor has recommended a kickspace heater about 8K BTU at 180. Stage 1 of this thermostat would be the radiant heat, the second stage would be the heater. The thermostat would be changed to a TH8320R1003. A C7189R1004 wireless sensor would be added to the living room area so that the thermostat can average the temperature reading between the two.

Seems a little complicated. But I wanted to get a sense of general options of how to add a 2nd stage in terms of adding wireless technology to get 2 phases. Is that the only way to do it?

In terms of why the kickspace as opposed to say a panel rad. Mostly it's one of space and finding something less conspicuous.

Would appreciate any guidance.

Rich_49

What are the " too high temps " ?
What are the finish floor materials ?
What type of home is it , old , new , leaky , tight ?
Does the radiant system keep the house warm during high demand times or is it just the water temps that concern you ?

Have you thought of adding a bit of radiant wall instead that operates with the floor system and would lower your temp requirement while increasing output . You will have to perform a bit of work in either case , that work does not have to further require complication .

Jim46

Rich, 100 year old house. Not well insulated. I have decent windows. But to give you a data point. If the house is at 73 and I turn off the stat, it drops about 1 degree per 2 hours. Which I don't think is too bad. Water temp can get to 160. The system is extremely comfortable. Very warm. We have old original floors. But opening the walls to put radiant .. can't do. It will be a mess of plaster. I'd rather add the heater. The system is phenomenal but the water is running too high on very cold days. Always in the plan to add the 2nd stage but since there was no hurry, we waited a winter too see how the radiant performed.

Rich_49

What kind of radiant install is it ? Plates , suspended tube ? If the surface temps are not too high to damage floor coverings there is no issue regardless of water temp , you may however take an efficiency hit .
How many winters has this system been up and running ?

SWEI

How was the tubing installed? Is there insulation under the floor? Are you trying to do temperature setbacks?

Jim46

This is plates with pex tubing in the plates attached to the subfloor. Also there is insulation under the plates. System running for 3 years. No damage to floor. There are a few gaps in the floor between the wood but the gaps were there prior to the radiant and look fine considering the age of house looks fine. I took pictures of the floor before the radiant and there's no change. Again, no comfort issue. We had simply always had a plan to put this 2nd phase to be more preventative. I have seen at sub 10 degree (which is not more than 1-2 weeks a year), the water temp get higher than 160.

It's more cautionary thing as to add the kickspace. No doubt I with poorly insulated walls I am losing efficiency. But I am OK with that.

SWEI

Is the house balloon-framed? If so, you may be able to insulate the walls without too much expense.

Are you doing temp setbacks?

Charlie from wmass

Perimeter baseboard panel may be enough to drop the water temperature. I would install it to run as a single stage as the more heat emitter that you have even at a lower temperature the more efficient your system will be.

Jim46

SWEI - i had never heard of temperature setback and was reading a little on it. Looks like I do that by nature by reducing the temperature manually when it reaches the set point. My heating bills even in my old house have been low as I essentially have the heat on for 1 long cycle each day. But I was doing this mostly to protect the floor and avoid a lot of cycling. Is there a gizmo that does this automatically?

For the insulation - I don't know how to assess if its balloon framed. However, I have received a couple of recommendations on blown in insulation. I'm not for doing that. Consulted with a specialist in older homes that indicated it has to be done with a vapor barrier on the inside face of the outside wall to prevent moisture build up. It's not a slam dunk on whether to it . Attic can be insulated.

Rich_49

What type of boiler is in the house ?

A second stage does unnecessarily complicate things as stated above , you could run all these things as a single system and lower water temps all the time .

One such gizmo is a Taco I Series ODR mixing valve . I might also preempt a concern many bring up , It is not always necessary to use P/S piping to utilize a mixing valve . TBD for your system

http://www.taco-hvac.com/uploads/FileLibrary/100-19.pdf

Jim46

Charlie. Do you recommend this over kickspace heater? If so why? Does this still have to be tied to the thermostat of the floor heat? This actually was the essence of my original post.. trying to understand how do you control radiant and a radiator/baseboard on the same room. Seems like 1 thermostat and a sensor is the only way to do it. But I'd like to check.

Charlie from wmass

The thermostat should be a set it and forget it for radiant. Steady even heat throughout the day is best for fuel savings.

Charlie from wmass

It is simply added to the system. It runs when the radiant runs. But I think your manipulation of the thermostat is the crux of the issue. Radiant should simply run with an outdoor reset adjusting the water temperature based on delta T between indoor target temperature and outdoor temperature.

Jim46

Condensing boiler Rich and system is on an outdoor reset. There is a mixing valve. The challenge is that that when it's colder, the water has to run high too high to make it comfortable at 68. Something needs to supplement the radiant.

Rich_49

How many rooms are a problem ? How many zones do you have ?

An extra port on a manifold with homerun to baseboard is all it would take to solve the issue probably . Determine how many BTUh you are short on those days when the temps get too high for your liking and size the supplemental baseboard/s for a like temp to what the radiant tubing will utilize . What are your high and low SWTs like now and who determined the reset curve and based on what information ?

Where is the mixing valve that is installed now , is it for hot water ?

Is it a modulating condensing boiler ? What brand , model ?

Jim46

The outdoor reset is set and there is a mixing valve. I have BB upstairs. The radiant and the baseboard I have witnessed running at different temps so the mixing valve does its job. Also I know the outdoor reset works because I can see the boiler capping at 150 even if my son tries to jack up the temp to 78. The rooms won't budge above 70 even though the water temp could go higher.

The dilemma is that when it's very cold, the water to the radiant can get to the same temp as that running for the BB. That's what concerns me. I want to cap the radiant at 140 and have something else kick in unless there is a simpler option. For example should i add another radiator and have it run on it's own thermostat? Surely there must be a standard practice on supplementing radiant.

hot_rod

I would take Kurts suggestion to upgrade the insulation and infiltration first. Some additional insulation where possible and cans of spray down to tighten up the air leaks.

Secondly add a control to allow outdoor and indoor reset, adjusting the supply temperature based on those inputs.

As a last step add additional emitters. Panel radiators or towel bars are a few other options, if you don't want to blow warm air with a kick space heater.

Jim46

Definitely modulating condensing.. Can't recall the brand/model.. will check when I get back home. There is separate mixing valve just for the radiant. There is 1 thermostat so I assume that is 1 zone for the first floor. Not a big house that multiple controls are needed. The rooms are connected together in an open floor plan. Is baseboard a better option that kickspace? I like my wood baseboard and prefer to not take that our for heating baseboard. what's wrong with kickspace heaters.... We can get a 19 inch long one that would do the trick and the back side would stick into a coat closet so it doesn't hog up all the wall.

Rich_49

Add a radiator but forget about another thermostat , you do not need one . What you need is to run tubing to your new radiator/s and let it run when the radiant runs , that is supplemental . Make that baseboard as long as you can and if you can do 2 in different areas go ahead . This will run whenever the radiant does and both will use the same water temp . This temp should be lower and the reset curve can be adjusted based on the new temp requirement as you have added radiation .

You'll also not need anything electrical done . The current emitter is not large enough so you add more to get where you want to be . It really is that simple .

Jim46

Thanks Rich. Are there radiators that you would recommend for this purpose. Something not too obtrusive. Is your qualm on kickspace the electrical connection?

SWEI

The existing mixing valve should probably be replaced with an iSeries-R valve (Rich posted a link.)

Do not start buying and installing extra bits before you have a proper analysis of the system (which includes the house, BTW.) You need a room-by-room heat loss analysis and a radiation survey at a minimum. Without those, we're all just guessing.

Where are you located? We might know someone who can help.

Charlie from wmass

One issue with a kickspace heater is it is designed to not turn on until it reaches 140 degrees without modifications. Using air to heat a room is contrary to the idea of using radiant heating to heat the room. As SWEI said we are really just guessing without detailed information about the system.

Jim46

140 is actually exactly when I would want the kickspace to turn on. Detailed analysis was done by the original designer and it was always planned for a 2nd stage and also as a second phase.

The radiant works quite well from a comfort level. When I looked at the thermostat gauges one day at the radiant manifold however, I got a little paranoid. I don't have floor damage nor do the floors feel hot. So maybe I don't need the supplement since I'm not cold. Very hard to know what to do. I'm not rolling in dough to spend what I want. When we hit zero degrees, the water temp did go to 180.

My concern expressed in the initial post was around this 2 phase thermostat with sensor... this seemed complicated to me.

Could a kick space heater be rigged up to simply come on when the water temp is 140? For me, the pros on it space. It simple takes up less space. Putting in baseboard ...I'll look into it. Just hate that it eats of floor space, not the best for little kids running into things.

As much as I would like to have great efficiency.. my heating bills are not bad at all as is.

I'm in North Hempstead area in NY - If there are contractors in the area knowledgeable on this topic let me know.

hot_rod

I was in a restaurant in Vt recently and the entire front wall had Heating Edge, high out BB. I can't imagine a more severe environment for baseboard. It looked great, no missing splice pieces, dings, or damaged fins.

But still not convinced you need additional emitters without some number crunching.


http://smithsenvironmental.com/products/he2-heating-edge-baseboard/

SWEI

https://heatinghelp.com/find-a-contractor/detail/technical-heating

Jim46

This board rocks... much gratitude for the kind help from everyone. Hope I can return the favor.

Jim46

Actually Rich-- if you're still there.... forgot to ask, you said "If the surface temps are not too high to damage floor coverings there is no issue regardless of water temp , you may however take an efficiency hit . " ,,, what temp is "too high". Any rule of thumb?

Rich_49

You would prefer Return water temps below 130*

Firecontrol933

I would suggest before you go through the expense and effort to install an 8K toe space unit that you experiment with a small electric heater of about the same output to see if that "little" amount of extra btu's is going to do what you need it to. If the room/space is that close to being heated sufficiently (8K) then I would first look at either upgrading the insulation under the current radiant or do as others have suggested and see what other things can be done to lessen the btu needs of the space by sealing air infiltration or adding insulation where feasible.

Gordy

Actually 8k is not a small amount especially for supplemental heating. Most avg. sized rooms in avg. envelopes may be less than , or equal that loss.

Firecontrol933

My "little" comment was intended to simply say that maybe an experiment would be in order to insure that the added amount would in fact resolve the issue before spending the money to install the heater.